Kea Administrator Reference Manual
This is the reference guide for Kea version 1.4.0.
Copyright (c) 2010-2018 Internet Systems Consortium, Inc. ("ISC")
Abstract
Kea is an open source implementation of the Dynamic Host Configuration
Protocol (DHCP) servers, developed and maintained by Internet Systems
Consortium (ISC).
This is the reference guide for Kea version 1.4.0. The most up-to-date
version of this document (in PDF, HTML, and plain text formats), along
with other documents for Kea, can be found at http://kea.isc.org/docs.
--------------------------------------------------------------------------
Table of Contents
1. Introduction
1.1. Supported Platforms
1.2. Required Software at Run-time
1.3. Kea Software
2. Quick Start
2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services
2.2. Running the Kea Servers Directly
3. Installation
3.1. Packages
3.2. Installation Hierarchy
3.3. Building Requirements
3.4. Installation from Source
3.4.1. Download Tar File
3.4.2. Retrieve from Git
3.4.3. Configure Before the Build
3.4.4. Build
3.4.5. Install
3.5. Selecting the Configuration Backend
3.6. DHCP Database Installation and Configuration
3.6.1. Building with MySQL Support
3.6.2. Building with PostgreSQL support
3.6.3. Building with CQL (Cassandra) support
4. Kea Database Administration
4.1. Databases and Database Version Numbers
4.2. The kea-admin Tool
4.3. Supported Databases
4.3.1. memfile
4.3.2. MySQL
4.3.3. PostgreSQL
4.3.4. CQL (Cassandra)
4.3.5. Using Read-Only Databases with Host
Reservations
4.3.6. Limitations Related to the use of SQL
Databases
5. Kea Configuration
5.1. JSON Configuration
5.1.1. JSON Syntax
5.1.2. Simplified Notation
6. Managing Kea with keactrl
6.1. Overview
6.2. Command Line Options
6.3. The keactrl Configuration File
6.4. Commands
6.5. Overriding the Server Selection
7. Kea Control Agent
7.1. Overview
7.2. Configuration
7.3. Secure Connections
7.4. Control Agent Limitations
7.5. Starting Control Agent
7.6. Connecting to the Control Agent
8. The DHCPv4 Server
8.1. Starting and Stopping the DHCPv4 Server
8.2. DHCPv4 Server Configuration
8.2.1. Introduction
8.2.2. Lease Storage
8.2.3. Hosts Storage
8.2.4. Interface Configuration
8.2.5. Issues with Unicast Responses to
DHCPINFORM
8.2.6. IPv4 Subnet Identifier
8.2.7. Configuration of IPv4 Address Pools
8.2.8. Standard DHCPv4 Options
8.2.9. Custom DHCPv4 options
8.2.10. DHCPv4 Private Options
8.2.11. DHCPv4 Vendor Specific Options
8.2.12. Nested DHCPv4 Options (Custom Option
Spaces)
8.2.13. Unspecified Parameters for DHCPv4 Option
Configuration
8.2.14. Stateless Configuration of DHCPv4
Clients
8.2.15. Client Classification in DHCPv4
8.2.16. DDNS for DHCPv4
8.2.17. Next Server (siaddr)
8.2.18. Echoing Client-ID (RFC 6842)
8.2.19. Using Client Identifier and Hardware
Address
8.2.20. DHCPv4-over-DHCPv6: DHCPv4 Side
8.3. Host Reservation in DHCPv4
8.3.1. Address Reservation Types
8.3.2. Conflicts in DHCPv4 Reservations
8.3.3. Reserving a Hostname
8.3.4. Including Specific DHCPv4 Options in
Reservations
8.3.5. Reserving Next Server, Server Hostname
and Boot File Name
8.3.6. Reserving Client Classes in DHCPv4
8.3.7. Storing Host Reservations in MySQL,
PostgreSQL or Cassandra
8.3.8. Fine Tuning DHCPv4 Host Reservation
8.4. Shared networks in DHCPv4
8.4.1. Local and relayed traffic in shared
networks
8.4.2. Client classification in shared networks
8.4.3. Host reservations in shared networks
8.5. Server Identifier in DHCPv4
8.6. How the DHCPv4 Server Selects a Subnet for the Client
8.6.1. Using a Specific Relay Agent for a Subnet
8.6.2. Segregating IPv4 Clients in a Cable
Network
8.7. Duplicate Addresses (DHCPDECLINE Support)
8.8. Statistics in the DHCPv4 Server
8.9. Management API for the DHCPv4 Server
8.10. Supported DHCP Standards
8.11. User contexts in IPv4
8.12. DHCPv4 Server Limitations
8.13. Kea DHCPv4 server examples
9. The DHCPv6 Server
9.1. Starting and Stopping the DHCPv6 Server
9.2. DHCPv6 Server Configuration
9.2.1. Introduction
9.2.2. Lease Storage
9.2.3. Hosts Storage
9.2.4. Interface Selection
9.2.5. IPv6 Subnet Identifier
9.2.6. Unicast Traffic Support
9.2.7. Subnet and Address Pool
9.2.8. Subnet and Prefix Delegation Pools
9.2.9. Prefix Exclude Option
9.2.10. Standard DHCPv6 Options
9.2.11. Common Softwire46 Options
9.2.12. Custom DHCPv6 Options
9.2.13. DHCPv6 Vendor-Specific Options
9.2.14. Nested DHCPv6 Options (Custom Option
Spaces)
9.2.15. Unspecified Parameters for DHCPv6 Option
Configuration
9.2.16. IPv6 Subnet Selection
9.2.17. Rapid Commit
9.2.18. DHCPv6 Relays
9.2.19. Relay-Supplied Options
9.2.20. Client Classification in DHCPv6
9.2.21. DDNS for DHCPv6
9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side
9.3. Host Reservation in DHCPv6
9.3.1. Address/Prefix Reservation Types
9.3.2. Conflicts in DHCPv6 Reservations
9.3.3. Reserving a Hostname
9.3.4. Including Specific DHCPv6 Options in
Reservations
9.3.5. Reserving Client Classes in DHCPv6
9.3.6. Storing Host Reservations in MySQL,
PostgreSQL or Cassandra
9.3.7. Fine Tuning DHCPv6 Host Reservation
9.4. Shared networks in DHCPv6
9.4.1. Local and relayed traffic in shared
networks
9.4.2. Client classification in shared networks
9.4.3. Host reservations in shared networks
9.5. Server Identifier in DHCPv6
9.6. Stateless DHCPv6 (Information-Request Message)
9.7. Support for RFC 7550
9.8. Using Specific Relay Agent for a Subnet
9.9. Segregating IPv6 Clients in a Cable Network
9.10. MAC/Hardware Addresses in DHCPv6
9.11. Duplicate Addresses (DECLINE Support)
9.12. Statistics in the DHCPv6 Server
9.13. Management API for the DHCPv6 Server
9.14. User contexts in IPv6
9.15. Supported DHCPv6 Standards
9.16. DHCPv6 Server Limitations
9.17. Kea DHCPv6 server examples
10. Lease Expiration in DHCPv4 and DHCPv6
10.1. Lease Reclamation
10.2. Configuring Lease Reclamation
10.3. Configuring Lease Affinity
10.4. Default Configuration Values for Leases Reclamation
10.5. Reclaiming Expired Leases with Command
11. The DHCP-DDNS Server
11.1. Overview
11.1.1. DNS Server selection
11.1.2. Conflict Resolution
11.1.3. Dual Stack Environments
11.2. Starting and Stopping the DHCP-DDNS Server
11.3. Configuring the DHCP-DDNS Server
11.3.1. Global Server Parameters
11.3.2. TSIG Key List
11.3.3. Forward DDNS
11.3.4. Reverse DDNS
11.3.5. User context in DDNS
11.3.6. Example DHCP-DDNS Server Configuration
11.4. DHCP-DDNS Server Limitations
12. The LFC process
12.1. Overview
12.2. Command Line Options
13. Client Classification
13.1. Client Classification Overview
13.2. Builtin Client Classes
13.3. Using Expressions In Classification
13.3.1. Logical operators
13.3.2. Substring
13.3.3. Concat
13.3.4. Ifelse
13.4. Configuring Classes
13.5. Using Static Host Reservations In Classification
13.6. Configuring Subnets With Class Information
13.7. Configuring Pools With Class Information
13.8. Using Classes
13.9. Classes and Hooks
13.10. Debugging Expressions
14. Hooks Libraries
14.1. Introduction
14.2. Installing Hook packages
14.3. Configuring Hooks Libraries
14.4. Available Hooks Libraries
14.4.1. user_chk: Checking User Access
14.4.2. legal_log: Forensic Logging Hooks
14.4.3. flex_id: Flexible Identifiers for Host
Reservations
14.4.4. host_cmds: Host Commands
14.4.5. lease_cmds: Lease Commands
14.4.6. subnet_cmds: Subnet Commands
14.4.7. ha: High Availability
14.4.8. radius: RADIUS server support
14.4.9. host_cache: Caching Host Reservations
14.4.10. stat_cmds: Supplemental Statistics
Commands
14.5. User contexts
15. Statistics
15.1. Statistics Overview
15.2. Statistics Lifecycle
15.3. Commands for Manipulating Statistics
15.3.1. statistic-get command
15.3.2. statistic-reset command
15.3.3. statistic-remove command
15.3.4. statistic-get-all command
15.3.5. statistic-reset-all command
15.3.6. statistic-remove-all command
16. Management API
16.1. Data Syntax
16.2. Using the Control Channel
16.3. Commands Supported by Both the DHCPv4 and DHCPv6
Servers
16.3.1. build-report
16.3.2. config-get
16.3.3. config-reload
16.3.4. config-test
16.3.5. config-write
16.3.6. leases-reclaim
16.3.7. libreload
16.3.8. list-commands
16.3.9. config-set
16.3.10. shutdown
16.3.11. dhcp-disable
16.3.12. dhcp-enable
16.3.13. version-get
16.4. Commands Supported by Control Agent
17. The libdhcp++ Library
17.1. Interface detection and Socket handling
18. Logging
18.1. Logging Configuration
18.1.1. Loggers
18.1.2. Logging Message Format
18.1.3. Logging During Kea Startup
19. The Kea Shell
19.1. Overview
19.2. Shell Usage
20. Frequently Asked Questions
20.1. General Frequently Asked Questions
20.1.1. Where did the Kea name came from?
20.1.2. Feature X is not supported yet. When/if
will it be available?
20.2. Frequently Asked Questions about DHCPv4
20.2.1. I set up a firewall, but the Kea server
still receives the traffic. Why?
20.3. Frequently Asked Questions about DHCPv6
20.3.1. Kea DHCPv6 doesn't seem to get incoming
traffic. I checked with tcpdump (or other
traffic capture software) that the incoming
traffic is reaching the box. What's wrong?
21. Acknowledgments
List of Tables
4.1. List of available backends
8.1. List of standard DHCPv4 options
8.2. List of standard DHCP option types
8.3. Default FQDN Flag Behavior
8.4. DHCPv4 Statistics
9.1. List of Standard DHCPv6 Options
9.2. List of Experimental DHCPv6 Options
9.3. Default FQDN Flag Behavior
9.4. DHCPv6 Statistics
11.1. Our example network
11.2. Forward DDNS Domains Needed
11.3. Reverse DDNS Domains Needed
13.1. List of Classification Values
13.2. List of Classification Expressions
14.1. List of available hooks libraries
14.2. Default behavior of the server in various HA states
18.1. List of loggers supported by Kea servers and hooks libraries shipped
with Kea and premium packages
Chapter 1. Introduction
Table of Contents
1.1. Supported Platforms
1.2. Required Software at Run-time
1.3. Kea Software
Kea is the next generation of DHCP software developed by ISC. It supports
both DHCPv4 and DHCPv6 protocols along with their extensions, e.g. prefix
delegation and dynamic updates to DNS.
Kea was initially developed as a part of the BIND 10 framework. In early
2014, ISC made the decision to discontinue active development of BIND 10
and continue development of Kea as standalone DHCP software.
This guide covers Kea version 1.4.0.
1.1. Supported Platforms
Kea is officially supported on Red Hat Enterprise Linux, CentOS, Fedora
and FreeBSD systems. It is also likely to work on many other platforms:
Kea 1.4.0 builds have been tested on (in no particular order) Red Hat
Enterprise Linux 6.4, Debian GNU/Linux 7, Ubuntu 14.04, Ubuntu 16.04,
Fedora 25, Fedore 26, Fedora 27, CentOS Linux 7, FreeBSD 11.0 OS X 10.11,
OS X 10.12, Debian 7.11, Debian 9
There are currently no plans to port Kea to Windows platforms.
1.2. Required Software at Run-time
Running Kea uses various extra software which may not be provided in the
default installation of some operating systems, nor in the standard
package collections. You may need to install this required software
separately. (For the build requirements, also see Section 3.3, "Building
Requirements".)
* Kea supports two crypto libraries: Botan and OpenSSL. Only one of them
is required to be installed during compilation. Kea uses the Botan
crypto library for C++ (http://botan.randombit.net/), version 1.9 or
later. As an alternative to Botan, Kea can use the OpenSSL crypto
library (http://www.openssl.org/), version 1.0.1 or later.
* Kea uses the log4cplus C++ logging library
(http://log4cplus.sourceforge.net/). It requires log4cplus version
1.0.3 or later.
* In order to store lease information in a MySQL database, Kea requires
MySQL headers and libraries. This is an optional dependency in that
Kea can be built without MySQL support.
* In order to store lease information in a PostgreSQL database, Kea
requires PostgreSQL headers and libraries. This is an optional
dependency in that Kea can be built without PostgreSQL support.
* In order to store lease information in a Cassandra database (CQL), Kea
requires Cassandra headers and libraries. This is an optional
dependency in that Kea can be built without Cassandra support.
1.3. Kea Software
Kea is modular. Part of this modularity is accomplished using multiple
cooperating processes which, together, provide the server functionality.
The following software is included with Kea:
* keactrl -- Tool to start, stop, reconfigure, and report status for the
Kea servers.
* kea-dhcp4 -- The DHCPv4 server process. This process responds to
DHCPv4 queries from clients.
* kea-dhcp6 -- The DHCPv6 server process. This process responds to
DHCPv6 queries from clients.
* kea-dhcp-ddns -- The DHCP Dynamic DNS process. This process acts as an
intermediary between the DHCP servers and DNS servers. It receives
name update requests from the DHCP servers and sends DNS Update
messages to the DNS servers.
* kea-admin -- A useful tool for database backend maintenance (creating
a new database, checking versions, upgrading etc.)
* kea-lfc -- This process removes redundant information from the files
used to provide persistent storage for the memfile data base backend.
While it can be run standalone, it is normally run as and when
required by the Kea DHCP servers.
* kea-ctrl-agent -- Kea Control Agent (CA) is a daemon exposes a RESTful
control interface for managing Kea servers.
* kea-shell -- Simple text client that uses REST interface to connect to
Kea Control Agent.
* perfdhcp -- A DHCP benchmarking tool which simulates multiple clients
to test both DHCPv4 and DHCPv6 server performance.
The tools and modules are covered in full detail in this guide. In
addition, manual pages are also provided in the default installation.
Kea also provides C++ libraries and programmer interfaces for DHCP. These
include detailed developer documentation and code examples.
Chapter 2. Quick Start
Table of Contents
2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services
2.2. Running the Kea Servers Directly
This section describes the basic steps needed to get Kea up and running.
For further details, full customizations, and troubleshooting, see the
respective chapters in the Kea guide.
2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services
1. Install required run-time and build dependencies. See Section 3.3,
"Building Requirements" for details.
2. Download Kea source tarball from ISC.org downloads page or ISC ftp
server.
3. Extract the tarball. For example:
$ tar xvzf kea-1.4.0.tar.gz
4. Go into the source directory and run the configure script:
$ cd kea-1.4.0
$ ./configure [your extra parameters]
5. Build it:
$ make
6. Install it (by default it will be placed in /usr/local/, so it is
likely that you will need root privileges for this step):
# make install
7. Edit the Kea configuration files which by default are installed in the
[kea-install-dir]/etc/kea/ directory. These are: kea-dhcp4.conf,
kea-dhcp6.conf, kea-dhcp-ddns.conf and kea-ctrl-agent.conf, for DHCPv4
server, DHCPv6 server, D2 and Control Agent respectively.
8. In order to start the DHCPv4 server in background, run the following
command (as root):
# keactrl start -s dhcp4
Or run the following command to start DHCPv6 server instead:
# keactrl start -s dhcp6
Note that it is also possible to start all servers simultaneously:
$ keactrl start
9. Verify that Kea server(s) are running:
# keactrl status
A server status of "inactive" may indicate a configuration error.
Please check the log file (by default named
[kea-install-dir]/var/kea/kea-dhcp4.log,
[kea-install-dir]/var/kea/kea-dhcp6.log,
[kea-install-dir]/var/kea/kea-ddns.log or
[kea-install-dir]/var/kea/kea-ctrl-agent.log) for the details of the
error.
10. If the server has been started successfully, test that it is
responding to DHCP queries and that the client receives a
configuration from the server; for example, use the ISC DHCP client.
11. Stop running the server(s):
# keactrl stop
For instructions specific to your system, please read the system specific
notes, available on the Kea web site.
The details of keactrl script usage can be found in Chapter 6, Managing
Kea with keactrl.
2.2. Running the Kea Servers Directly
The Kea servers can be started directly, without the need to use the
keactrl. To start the DHCPv4 server run the following command:
# kea-dhcp4 -c /path/to/your/kea4/config/file.json
Similarly, to start the DHCPv6 server run the following command:
# kea-dhcp6 -c /path/to/your/kea6/config/file.json
Chapter 3. Installation
Table of Contents
3.1. Packages
3.2. Installation Hierarchy
3.3. Building Requirements
3.4. Installation from Source
3.4.1. Download Tar File
3.4.2. Retrieve from Git
3.4.3. Configure Before the Build
3.4.4. Build
3.4.5. Install
3.5. Selecting the Configuration Backend
3.6. DHCP Database Installation and Configuration
3.6.1. Building with MySQL Support
3.6.2. Building with PostgreSQL support
3.6.3. Building with CQL (Cassandra) support
3.1. Packages
Some operating systems or software package vendors may provide
ready-to-use, pre-built software packages for Kea. Installing a pre-built
package means you do not need to install the software required only to
build Kea and do not need to make the software.
3.2. Installation Hierarchy
The following is the directory layout of the complete Kea installation.
(All directory paths are relative to the installation directory):
* bin/ -- utility programs.
* etc/kea/ -- configuration files.
* include/ -- C++ development header files.
* lib/ -- libraries.
* lib/hooks -- additional hooks libraries.
* sbin/ -- server software and commands used by the system
administrator.
* share/kea/ -- configuration specifications and examples.
* share/doc/kea/ -- this guide, other supplementary documentation, and
examples.
* share/man/ -- manual pages (online documentation).
* var/kea/ -- server identification, lease databases, and log files.
3.3. Building Requirements
In addition to the run-time requirements (listed in Section 1.2, "Required
Software at Run-time"), building Kea from source code requires various
development include headers and program development tools.
Note
Some operating systems have split their distribution packages into a
run-time and a development package. You will need to install the
development package versions, which include header files and libraries, to
build Kea from the source code.
Building from source code requires the following software installed on the
system:
* Boost C++ Libraries (http://www.boost.org/). The oldest Boost version
used for testing is 1.57 (it may work with older versions). Boost
system library is required. Building boost header only is no longer
recommended.
* Botan (at least version 1.9) or OpenSSL (at least version 1.0.1). Note
that Botan version 2 or later and OpenSSL version 1.0.2 or 1.1.0 or
later are strongly recommended.
* log4cplus (at least version 1.0.3) development include headers.
* A C++ compiler (with C++11 support) and standard development headers.
Kea builds have been tested with GCC g++ 4.7.2 4.7.3 4.8.2 4.8.4 4.8.5
4.9.3 4.9.4 5.3.1 5.4.0 6.3.0 6.3.1 clang-800.0.38 clang-802.0.42
clang-900.0.37
* The development tools automake, libtool, pkg-config.
* The MySQL client and the client development libraries, when using the
--with-mysql configuration flag to build the Kea MySQL database
backend. In this case an instance of the MySQL server running locally
or on a machine reachable over a network is required. Note that
running the unit tests requires a local MySQL server.
* The PostgreSQL client and the client development libraries, when using
the --with-pgsql configuration flag to build the Kea PostgreSQL
database backend. In this case an instance of the PostgreSQL server
running locally or on some other machine, reachable over the network
from the machine running Kea, is required. Note that running the unit
tests requires a local PostgreSQL server.
* Cpp-driver from DataStax is needed when using the --with-cql
configuration flag to build Kea with Cassandra database backend. In
this case an instance of the Cassandra server running locally or on
some other machine, reachable over the network from the machine
running Kea, is required. Note that running the unit tests requires a
local Cassandra server.
* googletest (version 1.8 or later), when using the --with-gtest
configuration option to build the unit tests.
* The documentation generation tools elinks, docbook-xsl, libxslt and
Doxygen, if using the --enable-generate-docs configuration option to
create the documentation.
Visit the user-contributed wiki at http://kea.isc.org/wiki/Install for
system-specific installation tips.
3.4. Installation from Source
Kea is open source software written in C++. It is freely available in
source code form from ISC as a downloadable tar file. A copy of the Kea
source code repository is accessible from Github
(https://github.com/isc-projects/kea). Kea may also be available in
pre-compiled ready-to-use packages from operating system vendors.
3.4.1. Download Tar File
The Kea release tarballs may be downloaded from:
http://ftp.isc.org/isc/kea/ (using FTP or HTTP).
3.4.2. Retrieve from Git
Downloading this "bleeding edge" code is recommended only for developers
or advanced users. Using development code in a production environment is
not recommended.
Note
When building from source code retrieved via Git, additional software will
be required: automake (v1.11 or later), libtoolize, and autoconf (v2.69 or
later). These may need to be installed.
The latest development code is available on Github (see
https://github.com/isc-projects/kea). The Kea source is public and
development is done in the "master" branch.
The code can be checked out from https://github.com/isc-projects/kea.git:
$ git clone https://github.com/isc-projects/kea.git
The code checked out from the git repository does not include the
generated configure script, Makefile.in files, nor their related build
files. They can be created by running autoreconf with the --install
switch. This will run autoconf, aclocal, libtoolize, autoheader, automake,
and related commands.
Write access to the Kea repository is only granted to ISC staff. If you
are a developer planning to contribute to Kea, please fork our Github
repository and use the "pull request" mechanism to request integration of
your code. Please consult https://help.github.com/articles/fork-a-repo/
for help on how to fork a Github repository. The Kea Developer's Guide
contains more information about the process, as well as describing the
requirements for contributed code to be accepted by ISC.
3.4.3. Configure Before the Build
Kea uses the GNU Build System to discover build environment details. To
generate the makefiles using the defaults, simply run:
$ ./configure
Run ./configure with the --help switch to view the different options. Some
commonly-used options are:
--prefix
Define the installation location (the default is /usr/local).
--with-boost-include
Define the path to find the Boost headers.
--with-botan-config
Specify the path to the botan-config script to build with Botan
for cryptographic functions.
--with-mysql
Build Kea with code to allow it to store leases and host
reservations in a MySQL database.
--with-pgsql
Build Kea with code to allow it to store leases and host
reservations in a PostgreSQL database.
--with-cql
Build Kea with code to allow it to store leases and host
reservations in a Cassandra (CQL) database.
--with-gtest, --with-gtest-source
Enable the building of the C++ Unit Tests using the Google Test
framework. This option specifies the path to the gtest source. (If
the framework is not installed on your system, it can be
downloaded from https://github.com/google/googletest.) from
https://github.com/google/googletest.)
--with-benchmark, --with-benchmark-source
Enable the building of the database backend benchmarks using the
Google Benchmark framework. This option specifies the path to the
gtest source. (If the framework is not installed on your system,
it can be downloaded from https://github.com/google/benchmark.)
--with-log4cplus
Define the path to find the Log4cplus headers and libraries.
--with-openssl
Replace Botan by the OpenSSL the cryptographic library. By default
configure searches for a valid Botan installation: if one is not
found, it searches for OpenSSL.
Note
For instructions concerning the installation and configuration of database
backends for Kea, see Section 3.6, "DHCP Database Installation and
Configuration". For information concerning the configuration backends, see
Section 3.5, "Selecting the Configuration Backend".
For example, the following command configures Kea to find the Boost
headers in /usr/pkg/include, specifies that PostgreSQL support should be
enabled, and sets the installation location to /opt/kea:
$ ./configure \
--with-boost-include=/usr/pkg/include \
--with-pgsql=/usr/local/bin/pg_config \
--prefix=/opt/kea
If you have some problems with building Kea using the header-only Boost
code or you'd like to use the Boost system library (assumed for the sake
of this example to be located in /usr/pkg/lib):
$ ./configure \
--with-boost-libs=-lboost_system \
--with-boost-lib-dir=/usr/pkg/lib
If configure fails, it may be due to missing or old dependencies.
If configure succeeds, it displays a report with the parameters used to
build the code. This report is saved into the file config.report and is
also embedded into the executable binaries, e.g., kea-dhcp4.
3.4.4. Build
After the configure step is complete, build the executables from the C++
code and prepare the Python scripts by running the command:
$ make
3.4.5. Install
To install the Kea executables, support files, and documentation, issue
the command:
$ make install
Do not use any form of parallel or job server options (such as GNU make's
-j option) when performing this step: doing so may cause errors.
Note
The install step may require superuser privileges.
If required, run ldconfig as root with /usr/local/lib (or with prefix/lib
if configured with --prefix) in /etc/ld.so.conf (or the relevant linker
cache configuration file for your OS):
$ ldconfig
Note
If you do not run ldconfig where it is required, you may see errors like
the following:
program: error while loading shared libraries: libkea-something.so.1:
cannot open shared object file: No such file or directory
3.5. Selecting the Configuration Backend
Kea 0.9 introduced configuration backends that are switchable during the
compilation phase. Only one backend, JSON, is currently supported.
JSON
JSON is the default configuration backend that allows Kea to read
JSON configuration files from disk. It does not require any
framework and thus is considered more lightweight. It allows
dynamic on-line reconfiguration using Kea API.
3.6. DHCP Database Installation and Configuration
Kea stores its leases in a lease database. The software has been written
in a way that makes it possible to choose which database product should be
used to store the lease information. At present, Kea supports four
database backends: MySQL, PostgreSQL, Cassandra and Memfile. To limit
external dependencies, MySQL, PostgreSQL and Cassandra support are
disabled by default and only Memfile is available. Support for the
optional external database backend must be explicitly included when Kea is
built. This section covers the building of Kea with one of the optional
backends and the creation of the lease database.
Note
When unit tests are built with Kea (the --with-gtest configuration option
is specified), the databases must be manually pre-configured for the unit
tests to run. The details of this configuration can be found in the Kea
Developer's Guide.
3.6.1. Building with MySQL Support
Install MySQL according to the instructions for your system. The client
development libraries must be installed.
Build and install Kea as described in Chapter 3, Installation, with the
following modification. To enable the MySQL database code, at the
"configure" step (see Section 3.4.3, "Configure Before the Build"), the
--with-mysql switch should be specified:
./configure [other-options] --with-mysql
If MySQL was not installed in the default location, the location of the
MySQL configuration program "mysql_config" should be included with the
switch, i.e.
./configure [other-options] --with-mysql=path-to-mysql_config
See Section 4.3.2.1, "First Time Creation of the MySQL Database" for
details regarding MySQL database configuration.
3.6.2. Building with PostgreSQL support
Install PostgreSQL according to the instructions for your system. The
client development libraries must be installed. Client development
libraries are often packaged as "libpq".
Build and install Kea as described in Chapter 3, Installation, with the
following modification. To enable the PostgreSQL database code, at the
"configure" step (see Section 3.4.3, "Configure Before the Build"), the
--with-pgsql switch should be specified:
./configure [other-options] --with-pgsql
If PostgreSQL was not installed in the default location, the location of
the PostgreSQL configuration program "pg_config" should be included with
the switch, i.e.
./configure [other-options] --with-pgsql=path-to-pg_config
See Section 4.3.3.1, "First Time Creation of the PostgreSQL Database" for
details regarding PostgreSQL database configuration.
3.6.3. Building with CQL (Cassandra) support
Install Cassandra according to the instructions for your system. The
Cassandra project website contains useful pointers:
http://cassandra.apache.org.
If you have a cpp-driver package available as binary or as source simply
install or build and install the package. Then build and install Kea as
described in Chapter 3, Installation: To enable the Cassandra (CQL)
database code, at the "configure" step (see Section 3.4.3, "Configure
Before the Build"), do:
./configure [other-options] --with-cql=path-to-pkg-config
Note if pkg-config is at its standard location (and thus in the shell
path) you do not need to supply its path. If it does not work (e.g. no
pkg-config, package not available in pkg-config with the cassandra name),
you can still use the cql_config script in tools/ as describe below.
Download and compile cpp-driver from DataStax. For details regarding
dependencies for building cpp-driver, see the project homepage
https://github.com/datastax/cpp-driver. In June 2016, the following
commands were used:
$ git clone https://github.com/datastax/cpp-driver
$ cd cpp-driver
$ mkdir build
$ cd build
$ cmake ..
$ make
As of June 2016, cpp-driver does not include cql_config script yet. Work
is in progress to contribute such a script to the cpp-driver project but,
until that is complete, intermediate steps that need to be conducted. A
cql_config script is present in the tools/ directory of the Kea sources.
Before using it, please create a cql_config_defines.sh in the same
directory (there is an example in cql_config_define.sh.sample available,
you may copy it over to cql_config_defines.sh and edit path specified in
it) and change the environment variable CPP_DRIVER_PATH to point to the
directory, where cpp-driver sources are located.
Build and install Kea as described in Chapter 3, Installation, with the
following modification. To enable the Cassandra (CQL) database code, at
the "configure" step (see Section 3.4.3, "Configure Before the Build"),
do:
./configure [other-options] --with-cql=path-to-cql_config
Chapter 4. Kea Database Administration
Table of Contents
4.1. Databases and Database Version Numbers
4.2. The kea-admin Tool
4.3. Supported Databases
4.3.1. memfile
4.3.2. MySQL
4.3.3. PostgreSQL
4.3.4. CQL (Cassandra)
4.3.5. Using Read-Only Databases with Host Reservations
4.3.6. Limitations Related to the use of SQL Databases
4.1. Databases and Database Version Numbers
Kea supports storing leases and host reservations (i.e. static assignments
of addresses, prefixes and options) in one of the several supported
databases. As future versions of Kea are released, the structure of those
databases will change. For example, Kea currently only stores lease
information and host reservations. Future versions of Kea will store
additional data such as subnet definitions: the database structure will
need to be updated to accommodate the extra information.
A given version of Kea expects a particular structure in the database and
checks for this by examining the version of database it is using. Separate
version numbers are maintained for backend databases, independent of the
version of Kea itself. It is possible that the backend database version
will stay the same through several Kea revisions: similarly, it is
possible that the version of backend database may go up several revisions
during a Kea upgrade. Versions for each database are independent, so an
increment in the MySQL database version does not imply an increment in
that of PostgreSQL.
Backend versions are specified in a major.minor format. The minor number
is increased when there are backward compatible changes introduced. For
example, the addition of a new index. It is desirable, but not mandatory
to apply such a change; you can run on older database version if you want
to. (Although, in the example given, running without the new index may be
at the expense of a performance penalty.) On the other hand, the major
number is increased when an incompatible change is introduced, for example
an extra column is added to a table. If you try to run Kea software on a
database that is too old (as signified by mismatched backend major version
number), Kea will refuse to run: administrative action will be required to
upgrade the database.
4.2. The kea-admin Tool
To manage the databases, Kea provides the kea-admin tool. It is able to
initialize a new database, check its version number, perform a database
upgrade, and dump lease data to a text file.
kea-admin takes two mandatory parameters: command and backend. Additional,
non-mandatory options may be specified. Currently supported commands are:
* lease-init -- Initializes a new lease database. This is useful during
a new Kea installation. The database is initialized to the latest
version supported by the version of the software being installed.
* lease-version -- Reports the lease database version number. This is
not necessarily equal to the Kea version number as each backend has
its own versioning scheme.
* lease-upgrade -- Conducts a lease database upgrade. This is useful
when upgrading Kea.
* lease-dump -- Dumps the contents of the lease database (for MySQL,
PostgreSQL or CQL backends) to a CSV (comma separated values) text
file. The first line of the file contains the column names. This is
meant to be used as a diagnostic tool, so it provides a portable,
human-readable form of the lease data.
backend specifies the backend type. Currently supported types are:
* memfile -- Lease information is stored on disk in a text file.
* mysql -- Lease information is stored in a MySQL relational database.
* pgsql -- Lease information is stored in a PostgreSQL relational
database.
* cql -- Lease information is stored in a CQL database.
Additional parameters may be needed, depending on your setup and specific
operation: username, password and database name or the directory where
specific files are located. See the appropriate manual page for details
(man 8 kea-admin).
4.3. Supported Databases
The following table presents the capabilities of available backends.
Please refer to the specific sections dedicated to each backend to better
understand their capabilities and limitations. Choosing the right backend
may be essential for success or failure of your deployment.
Table 4.1. List of available backends
+------------------------------------------------------------------------+
| Feature | Memfile | MySQL | PostgreSQL | CQL (Cassandra) |
|-------------------+----------+----------+------------+-----------------|
| Status | Stable | Stable | Stable | Experimental |
|-------------------+----------+----------+------------+-----------------|
| Data format | CSV file | SQL RMDB | SQL RMDB | NoSQL database |
| | | | | (CQL) |
|-------------------+----------+----------+------------+-----------------|
| Leases | yes | yes | yes | yes |
|-------------------+----------+----------+------------+-----------------|
| Host Reservations | no | yes | yes | yes |
|-------------------+----------+----------+------------+-----------------|
| Options defined | no | yes | yes | yes |
| on per host basis | | | | |
+------------------------------------------------------------------------+
4.3.1. memfile
The memfile backend is able to store lease information, but is not able to
store host reservation details: these must be stored in the configuration
file. (There are no plans to add a host reservations storage capability to
this backend.)
No special initialization steps are necessary for the memfile backend.
During the first run, both kea-dhcp4 and kea-dhcp6 will create an empty
lease file if one is not present. Necessary disk write permission is
required.
4.3.1.1. Upgrading Memfile Lease Files from an Earlier Version of Kea
There are no special steps required to upgrade memfile lease files from an
earlier version of Kea to a new version of Kea. During startup the servers
will check the schema version of the lease files against their own. If
there is a mismatch, the servers will automatically launch the LFC process
to convert the files to the server's schema version. While this mechanism
is primarily meant to ease the process of upgrading to newer versions of
Kea, it can also be used for downgrading should the need arise. When
upgrading, any values not present in the original lease files will be
assigned appropriate default values. When downgrading, any data present in
the files but not in the server's schema will be dropped. If you wish to
convert the files manually, prior to starting the servers you may do so by
running the LFC process yourself. See Chapter 12, The LFC process for more
information.
4.3.2. MySQL
MySQL is able to store leases, host reservations and options defined on a
per host basis. This section can be safely ignored if you chose to store
the data in other backends.
4.3.2.1. First Time Creation of the MySQL Database
If you are setting the MySQL database for the first time, you need to
create the database area within MySQL and set up the MySQL user ID under
which Kea will access the database. This needs to be done manually:
kea-admin is not able to do this for you.
To create the database:
1. Log into MySQL as "root":
$ mysql -u root -p
Enter password:
mysql>
2. Create the MySQL database:
mysql> CREATE DATABASE database-name;
(database-name is the name you have chosen for the database.)
3. Create the user under which Kea will access the database (and give it
a password), then grant it access to the database tables:
mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';
(user-name and password are the user ID and password you are using to
allow Keas access to the MySQL instance. All apostrophes in the
command lines above are required.)
4. At this point, you may elect to create the database tables.
(Alternatively, you can exit MySQL and create the tables using the
kea-admin tool, as explained below.) To do this:
mysql> CONNECT database-name;
mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql
(path-to-kea is the location where you installed Kea.)
5. Exit MySQL:
mysql> quit
Bye
$
If you elected not to create the tables in step 4, you can do so now by
running the kea-admin tool:
$ kea-admin lease-init mysql -u database-user -p database-password -n database-name
(Do not do this if you did create the tables in step 4.) kea-admin
implements rudimentary checks: it will refuse to initialize a database
that contains any existing tables. If you want to start from scratch, you
must remove all data manually. (This process is a manual operation on
purpose to avoid possibly irretrievable mistakes by kea-admin.)
4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea
Sometimes a new Kea version may use newer database schema, so there will
be a need to upgrade the existing database. This can be done using the
kea-admin lease-upgrade command.
To check the current version of the database, use the following command:
$ kea-admin lease-version mysql -u database-user -p database-password -n database-name
(See Section 4.1, "Databases and Database Version Numbers" for a
discussion about versioning.) If the version does not match the minimum
required for the new version of Kea (as described in the release notes),
the database needs to be upgraded.
Before upgrading, please make sure that the database is backed up. The
upgrade process does not discard any data but, depending on the nature of
the changes, it may be impossible to subsequently downgrade to an earlier
version. To perform an upgrade, issue the following command:
$ kea-admin lease-upgrade mysql -u database-user -p database-password -n database-name
4.3.3. PostgreSQL
PostgreSQL is able to store leases, host reservations and options defined
on a per host basis. A PostgreSQL database must be set up if you want Kea
to store lease and other information in PostgreSQL. This step can be
safely ignored if you are using other database backends.
4.3.3.1. First Time Creation of the PostgreSQL Database
The first task is to create both the lease database and the user under
which the servers will access it. A number of steps are required:
1. Log into PostgreSQL as "root":
$ sudo -u postgres psql postgres
Enter password:
postgres=#
2. Create the database:
postgres=# CREATE DATABASE database-name;
CREATE DATABASE
postgres=#
(database-name is the name you have chosen for the database.)
3. Create the user under which Kea will access the database (and give it
a password), then grant it access to the database:
postgres=# CREATE USER user-name WITH PASSWORD 'password';
CREATE ROLE
postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
GRANT
postgres=#
4. Exit PostgreSQL:
postgres=# \q
Bye
$
5. At this point you are ready to create the database tables. This can be
done using the kea-admin tool as explained in the next section
(recommended), or manually. To create the tables manually enter the
following command. Note that PostgreSQL will prompt you to enter the
new user's password you specified in Step 3. When the command
completes you will be returned to the shell prompt. You should see
output similar to following:
$ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
Password for user user-name:
CREATE TABLE
CREATE INDEX
CREATE INDEX
CREATE TABLE
CREATE INDEX
CREATE TABLE
START TRANSACTION
INSERT 0 1
INSERT 0 1
INSERT 0 1
COMMIT
CREATE TABLE
START TRANSACTION
INSERT 0 1
COMMIT
$
(path-to-kea is the location where you installed Kea.)
If instead you encounter an error like:
psql: FATAL: no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off
... you will need to alter the PostgreSQL configuration. Kea uses
password authentication when connecting to the database and must have
the appropriate entries added to PostgreSQL's pg_hba.conf file. This
file is normally located in the primary data directory for your
PostgreSQL server. The precise path may vary but the default location
for PostgreSQL 9.3 on Centos 6.5 is:
/var/lib/pgsql/9.3/data/pg_hba.conf.
Assuming Kea is running on the same host as PostgreSQL, adding lines
similar to following should be sufficient to provide
password-authenticated access to Kea's database:
local database-name user-name password
host database-name user-name 127.0.0.1/32 password
host database-name user-name ::1/128 password
These edits are primarily intended as a starting point not a
definitive reference on PostgreSQL administration or database
security. Please consult your PostgreSQL user manual before making
these changes as they may expose other databases that you run. It may
be necessary to restart PostgreSQL in order for these changes to take
effect.
4.3.3.2. Initialize the PostgreSQL Database Using kea-admin
If you elected not to create the tables manually, you can do so now by
running the kea-admin tool:
$ kea-admin lease-init pgsql -u database-user -p database-password -n database-name
Do not do this if you already created the tables in manually. kea-admin
implements rudimentary checks: it will refuse to initialize a database
that contains any existing tables. If you want to start from scratch, you
must remove all data manually. (This process is a manual operation on
purpose to avoid possibly irretrievable mistakes by kea-admin.)
4.3.3.3. Upgrading a PostgreSQL Database from an Earlier Version of Kea
The PostgreSQL database schema can be upgraded using the same tool and
commands as described in Section 4.3.2.2, "Upgrading a MySQL Database from
an Earlier Version of Kea", with the exception that the "pgsql" database
backend type must be used in the commands.
Use the following command to check the current schema version:
$ kea-admin lease-version pgsql -u database-user -p database-password -n database-name
Use the following command to perform an upgrade:
$ kea-admin lease-upgrade pgsql -u database-user -p database-password -n database-name
4.3.4. CQL (Cassandra)
Cassandra, or Cassandra Query Language (CQL), is the newest backend added
to Kea. Since it was added recently and has not undergone as much testing
as other backends, it is considered experimental. Please use with caution.
The Cassandra backend is able to store leases, host reservations and
options defined on a per host basis.
The CQL database must be properly set up if you want Kea to store
information in CQL. This section can be safely ignored if you chose to
store the data in other backends.
4.3.4.1. First Time Creation of the Cassandra Database
If you are setting up the CQL database for the first time, you need to
create the keyspace area within CQL. This needs to be done manually:
kea-admin is not able to do this for you.
To create the database:
1. Export CQLSH_HOST environment variable:
$ export CQLSH_HOST=localhost
2. Log into CQL:
$ cqlsh
cql>
3. Create the CQL keyspace:
cql> CREATE KEYSPACE keyspace-name WITH replication = {'class' : 'SimpleStrategy','replication_factor' : 1};
(keyspace-name is the name you have chosen for the keyspace)
4. At this point, you may elect to create the database tables.
(Alternatively, you can exit CQL and create the tables using the
kea-admin tool, as explained below) To do this:
cqslh -k keyspace-name -f path-to-kea/share/kea/scripts/cql/dhcpdb_create.cql
(path-to-kea is the location where you installed Kea)
If you elected not to create the tables in step 4, you can do so now by
running the kea-admin tool:
$ kea-admin lease-init cql -n database-name
(Do not do this if you did create the tables in step 4.) kea-admin
implements rudimentary checks: it will refuse to initialize a database
that contains any existing tables. If you want to start from scratch, you
must remove all data manually. (This process is a manual operation on
purpose to avoid possibly irretrievable mistakes by kea-admin)
4.3.4.2. Upgrading a CQL Database from an Earlier Version of Kea
Sometimes a new Kea version may use newer database schema, so there will
be a need to upgrade the existing database. This can be done using the
kea-admin lease-upgrade command.
To check the current version of the database, use the following command:
$ kea-admin lease-version cql -n database-name
(See Section 4.1, "Databases and Database Version Numbers" for a
discussion about versioning) If the version does not match the minimum
required for the new version of Kea (as described in the release notes),
the database needs to be upgraded.
Before upgrading, please make sure that the database is backed up. The
upgrade process does not discard any data but, depending on the nature of
the changes, it may be impossible to subsequently downgrade to an earlier
version. To perform an upgrade, issue the following command:
$ kea-admin lease-upgrade cql -n database-name
4.3.5. Using Read-Only Databases with Host Reservations
If a read-only database is used for storing host reservations, Kea must be
explicitly configured to operate on the database in read-only mode.
Sections Section 8.2.3.2, "Using Read-Only Databases for Host
Reservations" and Section 9.2.3.2, "Using Read-Only Databases for Host
Reservations" describe when such configuration may be required and how to
configure Kea to operate using a read-only host database.
4.3.6. Limitations Related to the use of SQL Databases
4.3.6.1. Year 2038 issue
The lease expiration time is stored in the SQL database for each lease as
a timestamp value. Kea developers observed that MySQL database doesn't
accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
from the beginning of the epoch. At the same time, some versions of
PostgreSQL do accept greater values but the value is altered when it is
read back. For this reason the lease database backends put the restriction
for the maximum timestamp to be stored in the database, which is equal to
the maximum signed 32-bit number. This effectively means that the current
Kea version can't store the leases which expiration time is later than
2147483647 seconds since the beginning of the epoch (around year 2038).
This will be fixed when the database support for longer timestamps is
available.
4.3.6.2. Server Terminates when Database Connection is Lost
If Kea is configured to use an external database it opens a connection to
the database and requires that this connection is not interrupted. When
the database connection breaks, e.g. as a result of SQL server restart,
DHCP servers will terminate indicating a fatal error. In such a case, the
system administrator is required to start the database and then "manually"
start Kea to resume the service.
Although the engineering team is planning to implement some form of
reconnect mechanism in the future, this will mostly be applicable in cases
when the database service is restarted and the connection down time is
relatively short. The DHCP server can't provide its service as long as the
database is down, because it can't store leases being assigned to the
clients. The server will have to reject any DHCP messages as long as the
connection is down and terminate if the reconnection attempt fails
multiple times.
Because the database connection is critical for the operation of the DHCP
service, the current behavior is to terminate when that connection is
unavailable to indicate that server is in inconsistent state and can't
serve clients.
Chapter 5. Kea Configuration
Table of Contents
5.1. JSON Configuration
5.1.1. JSON Syntax
5.1.2. Simplified Notation
Kea is using JSON structures to handle configuration. Previously we there
was a concept of other configuration backends, but that never was
implemented and the idea was abandoned.
5.1. JSON Configuration
JSON is notation used throughout the Kea project. The most obvious usage
is for configuration file, but it is also used for sending commands over
Management API (see Chapter 16, Management API) and for communicating
between DHCP servers and DDNS update daemon.
Typical usage assumes that the servers are started from the command line
(either directly or using a script, e.g. keactrl). The JSON backend uses
certain signals to influence Kea. The configuration file is specified upon
startup using the -c parameter.
5.1.1. JSON Syntax
Configuration files for DHCPv4, DHCPv6 and DDNS modules are defined in an
extended JSON format. Basic JSON is defined in RFC 7159. Note that Kea 1.2
introduces a new parser that is better at following the JSON spec. In
particular, the only values allowed for boolean are true or false (all
lowercase). The capitalized versions (True or False) are not accepted.
Kea components use an extended JSON with additional features allowed:
* shell comments: any text after the hash (#) character is ignored. Both
Dhcp4 and Dhcp6 allow # in any column, while Ddns requires hash to be
in the first column.
* C comments: any text after the double slashes (//) character is
ignored. Both Dhcp4 and Dhcp6 supports this feature.
* Multiline comments: any text between /* and */ is ignored. This
commenting can span multiple lines. Both Dhcp4 and Dhcp6 supports this
feature.
* File inclusion: JSON files can include other JSON files. This can be
done by using <?include "file.json"?>. Both Dhcp4 and Dhcp6 supports
this feature.
The configuration file consists of a single object (often colloquially
called a map) started with a curly bracket. It comprises the "Dhcp4",
"Dhcp6", "DhcpDdns" and/or "Logging" objects. It is possible to define
additional elements, but they will be ignored. For example, it is possible
to define Dhcp4, Dhcp6 and Logging elements in a single configuration file
that can be used to start both the DHCPv4 and DHCPv6 components. When
starting, the DHCPv4 component will use Dhcp4 object to configure itself
and the Logging object to configure logging parameters; it will ignore the
Dhcp6 object.
A very simple configuration for both DHCPv4 and DHCPv6 could look like
this:
# The whole configuration starts here.
{
# DHCPv4 specific configuration starts here.
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth0" ],
"dhcp-socket-type": "raw"
},
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet4": [{
"pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
"subnet": "192.0.2.0/24"
}]
},
# DHCPv4 specific configuration ends here.
# DHCPv6 specific configuration starts here.
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1" ]
},
"preferred-lifetime": 3000,
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet6": [{
"pools": [ { "pool": "2001:db8::/80" } ],
"subnet": "2001:db8::/64"
}]
},
# DHCPv6 specific configuration ends here.
# Logger parameters (that could be shared among several components) start here.
# This section is used by both the DHCPv4 and DHCPv6 servers.
"Logging": {
"loggers": [{
"name": "*",
"severity": "DEBUG"
}]
}
# Logger parameters end here.
# The whole configuration structure ends here.
}
More examples are available in the installed share/doc/kea/examples
directory.
To avoid repetition of mostly similar structures, examples in the rest of
this guide will showcase only the subset of parameters appropriate for a
given context. For example, when discussing the IPv6 subnets configuration
in DHCPv6, only subnet6 parameters will be mentioned. It is implied that
the remaining elements (the global map that holds Dhcp6, Logging and
possibly DhcpDdns) are present, but they are omitted for clarity. Usually,
locations where extra parameters may appear are denoted by an ellipsis.
5.1.2. Simplified Notation
It is sometimes convenient to refer to a specific element in the
configuration hierarchy. Each hierarchy level is separated by a slash. If
there is an array, a specific instance within that array is referenced by
a number in square brackets (with numbering starting at zero). For
example, in the above configuration the valid-lifetime in the Dhcp6
component can be referred to as Dhcp6/valid-lifetime and the pool in the
first subnet defined in the DHCPv6 configuration as Dhcp6/subnet6[0]/pool.
Chapter 6. Managing Kea with keactrl
Table of Contents
6.1. Overview
6.2. Command Line Options
6.3. The keactrl Configuration File
6.4. Commands
6.5. Overriding the Server Selection
6.1. Overview
keactrl is a shell script which controls the startup, shutdown and
reconfiguration of the Kea servers (kea-dhcp4, kea-dhcp6, kea-dhcp-ddns
and kea-ctrl-agent). It also provides the means for checking the current
status of the servers and determining the configuration files in use.
6.2. Command Line Options
keactrl is run as follows:
keactrl <command> [-c keactrl-config-file] [-s server[,server,..]]
<command> is the one of the commands described in Section 6.4, "Commands".
The optional -c keactrl-config-file switch allows specification of an
alternate keactrl configuration file. (--ctrl-config is a synonym for -c.)
In the absence of -c, keactrl will use the default configuration file
[kea-install-dir]/etc/kea/keactrl.conf.
The optional -s server[,server ...] switch selects the servers to which
the command is issued. (--server is a synonym for -s.) If absent, the
command is sent to all servers enabled in the keactrl configuration file.
If multiple servers are specified, they should be separated by commas with
no intervening spaces.
6.3. The keactrl Configuration File
Depending on requirements, not all of the available servers need be run.
The keactrl configuration file sets which servers are enabled and which
are disabled. The default configuration file is
[kea-install-dir]/etc/kea/keactrl.conf, but this can be overridden on a
per-command basis using the -c switch.
The contents of keactrl.conf are:
# This is a configuration file for keactrl script which controls
# the startup, shutdown, reconfiguration and gathering the status
# of the Kea's processes.
# prefix holds the location where the Kea is installed.
prefix=@prefix@
# Location of Kea configuration file.
kea_dhcp4_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp4.conf
kea_dhcp6_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp6.conf
kea_dhcp_ddns_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp-ddns.conf
kea_ctrl_agent_config_file=@sysconfdir@/@PACKAGE@/kea-ctrl-agent.conf
# Location of Kea binaries.
exec_prefix=@exec_prefix@
dhcp4_srv=@sbindir@/kea-dhcp4
dhcp6_srv=@sbindir@/kea-dhcp6
dhcp_ddns_srv=@sbindir@/kea-dhcp-ddns
ctrl_agent_srv=@sbindir@/kea-ctrl-agent
# Start DHCPv4 server?
dhcp4=yes
# Start DHCPv6 server?
dhcp6=yes
# Start DHCP DDNS server?
dhcp_ddns=no
# Start Control Agent?
ctrl_agent=yes
# Be verbose?
kea_verbose=no
The dhcp4, dhcp6, dhcp_ddns and ctrl_agent parameters set to "yes"
configure keactrl to manage (start, reconfigure) all servers, i.e.
kea-dhcp4, kea-dhcp6, kea-dhcp-ddns and kea-ctrl-agent. When any of these
parameters is set to "no" the keactrl will ignore the corresponding server
when starting or reconfiguring Kea.
By default, Kea servers managed by keactrl are located in
[kea-install-dir]/sbin. This should work for most installations. If the
default location needs to be altered for any reason, the paths specified
with the dhcp4_srv, dhcp6_srv, dhcp_ddns_srv and ctrl_agent_srv parameters
should be modified.
The kea_verbose parameter specifies the verbosity of the servers being
started. When kea_verbose is set to "yes" the logging level of the server
is set to DEBUG. Modification of the logging severity in a configuration
file, as described in Chapter 18, Logging, will have no effect as long as
the kea_verbose is set to "yes". Setting it to "no" will cause the server
to use the logging levels specified in the Kea configuration file for
respective loggers. If no logging configuration is specified, the default
settings will be used.
Note
The verbosity for the server is set when it is started. Once started, the
verbosity can be only changed by stopping the server and starting it again
with the new value of the kea_verbose parameter.
6.4. Commands
The following commands are supported by keactrl:
* start - starts selected servers.
* stop - stops all running servers.
* reload - triggers reconfiguration of the selected servers by sending
the SIGHUP signal to them.
* status - returns the status of the servers (active or inactive) and
the names of the configuration files in use.
Typical output from keactrl when starting the servers looks similar to the
following:
$ keactrl start
INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea-dhcp4.conf -d
INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea-dhcp6.conf -d
INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea-dhcp-ddns.conf -d
INFO/keactrl: Starting kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf -d
Kea's servers create PID files upon startup. These files are used by
keactrl to determine whether or not a given server is running. If one or
more servers are running when the start command is issued, the output will
look similar to the following:
$ keactrl start
INFO/keactrl: kea-dhcp4 appears to be running, see: PID 10918, PID file: /usr/local/var/kea/kea.kea-dhcp4.pid.
INFO/keactrl: kea-dhcp6 appears to be running, see: PID 10924, PID file: /usr/local/var/kea/kea.kea-dhcp6.pid.
INFO/keactrl: kea-dhcp-ddns appears to be running, see: PID 10930, PID file: /usr/local/var/kea/kea.kea-dhcp-ddns.pid.
INFO/keactrl: kea-ctrl-agent appears to be running, see: PID 10931, PID file: /usr/local/var/kea/kea.kea-ctrl-agent.pid.
During normal shutdowns these PID files are deleted. They may, however, be
left over as remnants following a system crash. It is possible, though
highly unlikely, that upon system restart the PIDs they contain actually
refer to processes unrelated to Kea. This condition will cause keactrl to
decide that the servers are running, when in fact they are not. In such a
case the PID files as listed in the keactrl output must be manually
deleted.
The following command stops all servers:
$ keactrl stop
INFO/keactrl: Stopping kea-dhcp4...
INFO/keactrl: Stopping kea-dhcp6...
INFO/keactrl: Stopping kea-dhcp-ddns...
INFO/keactrl: Stopping kea-ctrl-agent...
Note that the stop will attempt to stop all servers regardless of whether
they are "enabled" in the keactrl.conf. If any of the servers are not
running, an informational message is displayed as in the stop command
output below.
$ keactrl stop
INFO/keactrl: kea-dhcp4 isn't running.
INFO/keactrl: kea-dhcp6 isn't running.
INFO/keactrl: kea-dhcp-ddns isn't running.
INFO/keactrl: kea-ctrl-agent isn't running.
As already mentioned, the reconfiguration of each Kea server is triggered
by the SIGHUP signal. The reload command sends the SIGHUP signal to the
servers that are enabled in the keactrl configuration file and are
currently running. When a server receives the SIGHUP signal it re-reads
its configuration file and, if the new configuration is valid, uses the
new configuration. A reload is executed as follows:
$ keactrl reload
INFO/keactrl: Reloading kea-dhcp4...
INFO/keactrl: Reloading kea-dhcp6...
INFO/keactrl: Reloading kea-dhcp-ddns...
INFO/keactrl: Reloading kea-ctrl-agent...
If any of the servers are not running, an informational message is
displayed as in the reload command output below.
$ keactrl stop
INFO/keactrl: kea-dhcp4 isn't running.
INFO/keactrl: kea-dhcp6 isn't running.
INFO/keactrl: kea-dhcp-ddns isn't running.
INFO/keactrl: kea-ctrl-agent isn't running.
Note
Currently keactrl does not report configuration failures when the server
is started or reconfigured. To check if the server's configuration
succeeded the Kea log must be examined for errors. By default, this is
written to the syslog file.
Sometimes it is useful to check which servers are running. The status
reports this, typical output looking like:
$ keactrl status
DHCPv4 server: active
DHCPv6 server: inactive
DHCP DDNS: active
Control Agent: active
Kea configuration file: /usr/local/etc/kea/kea.conf
Kea DHCPv4 configuration file: /usr/local/etc/kea/kea-dhcp4.conf
Kea DHCPv6 configuration file: /usr/local/etc/kea/kea-dhcp6.conf
Kea DHCP DDNS configuration file: /usr/local/etc/kea/kea-dhcp-ddns.conf
Kea Control Agent configuration file: /usr/local/etc/kea/kea-ctrl-agent.conf
keactrl configuration file: /usr/local/etc/kea/keactrl.conf
6.5. Overriding the Server Selection
The optional -s switch allows the selection of the servers to which
keactrl command is issued. For example, the following instructs keactrl to
stop the kea-dhcp4 and kea-dhcp6 servers and leave the kea-dhcp-ddns and
kea-ctrl-agent running:
$ keactrl stop -s dhcp4,dhcp6
Similarly, the following will only start the kea-dhcp4 and kea-dhcp-ddns
servers and not: kea-dhcp6, kea-ctrl-agent.
$ keactrl start -s dhcp4,dhcp_ddns
Note that the behavior of the -s switch with the start and reload commands
is different to its behavior with the stop command. On start and reload,
keactrl will check if the servers given as parameters to the -s switch are
enabled in the keactrl configuration file: if not, the server will be
ignored. For stop however, this check is not made: the command is applied
to all listed servers, regardless of whether they have been enabled in the
file.
The following keywords can be used with the -s command line option:
* dhcp4 for kea-dhcp4.
* dhcp6 for kea-dhcp6.
* dhcp_ddns for kea-dhcp-ddns.
* ctrl_agent for kea-ctrl-agent.
* all for all servers (default).
Chapter 7. Kea Control Agent
Table of Contents
7.1. Overview
7.2. Configuration
7.3. Secure Connections
7.4. Control Agent Limitations
7.5. Starting Control Agent
7.6. Connecting to the Control Agent
7.1. Overview
Kea Control Agent (CA) is a daemon, first included in Kea 1.2, which
exposes a RESTful control interface for managing Kea servers. The daemon
can receive control commands over HTTP and either forward these commands
to the respective Kea servers or handle these commands on its own. The
determination whether the command should be handled by the CA or forwarded
is made by checking the value of the 'service' parameter which may be
included in the command from the controlling client. The details of the
supported commands as well as their structures are provided in Chapter 16,
Management API.
Hook libraries can be loaded by the CA to provide support for additional
commands or custom behavior of existing commands. Such hook libraries must
implement callouts for 'control_command_receive' hook point. Details about
creating new hook libraries and supported hook points can be found in Kea
Developer's Guide.
The CA processes received commands according to the following algorithm:
* Pass command into any installed hooks (regardless of service
value(s)). If the command is handled by a hook, return the response.
* If the service specifies one more or services, the CA will forward the
command to specified services and return the accumulated responses.
* If service is not specified or is an empty list, the CA will handle
the command if it supports it.
7.2. Configuration
The following example demonstrates the basic CA configuration.
{
"Control-agent": {
"http-host": "10.20.30.40",
"http-port": 8080,
"control-sockets": {
"dhcp4": {
"comment": "main server",
"socket-type": "unix",
"socket-name": "/path/to/the/unix/socket-v4"
},
"dhcp6": {
"socket-type": "unix",
"socket-name": "/path/to/the/unix/socket-v4",
"user-context": { "version": 3 }
}
},
"hooks-libraries": [
{
"library": "/opt/local/control-agent-commands.so",
"parameters": {
"param1": "foo"
}
} ]
},
"Logging": {
"loggers": [ {
"name": "kea-ctrl-agent",
"severity": "INFO"
} ]
}
}
The http-host and http-port specify an IP address and port to which HTTP
service will be bound. In case of the example configuration provided
above, the RESTful service will be available under the URL of
http://10.20.30.40:8080/. If these parameters are not specified, the
default URL is http://127.0.0.1:8000/
It has been mentioned in the Section 7.1, "Overview" that CA can forward
received commands to the specific Kea servers for processing. For example,
config-get is sent to retrieve configuration of one of the Kea services.
When CA receives this command, including a service parameter indicating
that the client desires to retrieve configuration of the DHCPv4 server,
the CA will forward this command to this server and then pass the received
response back to the client. More about the service parameter and general
structure of the commands can be found in Chapter 16, Management API.
The CA uses unix domain sockets to forward control commands and receive
responses from other Kea services. The dhcp4, dhcp6 and d2 maps specify
the files to which unix domain sockets are bound. In case of the
configuration above, the CA will connect to the DHCPv4 server via
/path/to/the/unix/socket-v4 to forward the commands to it. Obviously, the
DHCPv4 server must be configured to listen to connections via this same
socket. In other words, the command socket configuration for the DHCPv4
server and CA (for this server) must match. Consult the Section 8.9,
"Management API for the DHCPv4 Server" and the Section 9.13, "Management
API for the DHCPv6 Server" to learn how the socket configuration is
specified for the DHCPv4 and DHCPv6 services.
Warning
We have renamed "dhcp4-server", "dhcp6-server" and "d2-server" to "dhcp4",
"dhcp6" and "d2" respectively after release of Kea 1.2. If you are
migrating from Kea 1.2 you need to tweak your CA config to use this new
naming convention. We have made this incompatible change to facilitate
future use cases where it will be possible to specify additional values of
the "service" parameter to point to the particular instances of the Kea
servers, e.g. "dhcp4/3" pointing to the 3rd instance of the DHCPv4 server
in the multi-processed configuration. This is not yet supported but the
current renaming lays the ground for it.
User contexts can store arbitrary data as long as it is valid JSON syntax
and its top level element is a map (i.e. the data must be enclosed in
curly brackets). Some hook libraries may expect specific formatting,
though. Please consult specific hook library documentation for details.
User contexts can be specified on either global scope, control socket and
loggers. One other useful usage is the ability to store comments or
descriptions: the parser translates a "comment" entry into a user-context
with the entry, this allows to attach a comment inside the configuration
itself.
Hooks libraries can be loaded by the Control Agent just like to DHCPv4 and
DHCPv6 servers. It currently supports one hook point
'control_command_receive' which makes it possible to delegate processing
of some commands to the hooks library. The hooks-libraries list contains
the list of hooks libraries that should be loaded by the CA, along with
their configuration information specified with parameters.
Please consult Chapter 18, Logging for the details how to configure
logging. The CA's root logger's name is kea-ctrl-agent as given in the
example above.
7.3. Secure Connections
Control Agent doesn't natively support secure HTTP connections like SSL or
TLS. In order to setup secure connection please use one of the available
third party HTTP servers and configure it to run as a reverse proxy to the
Control Agent. Kea has been tested with two major HTTP server
implentations working as a reverse proxy: Apache2 and nginx. Example
configurations including extensive comments are provided in the
doc/examples/https/ directory.
The reverse proxy forwards HTTP requests received over secure connection
to the Control Agent using (not secured) HTTP. Typically, the reverse
proxy and the Control Agent are running on the same machine, but it is
possible to configure them to run on separate machines as well. In this
case, security depends on the protection of the communications between the
reverse proxy and the Control Agent.
Apart from providing the encryption layer for the control channel, a
reverse proxy server is also often used for authentication of the
controlling clients. In this case, the client must present a valid
certificate when it connects via reverse proxy. The proxy server
authenticates the client by checking if the presented certificate is
signed by the certificate authority used by the server.
To illustrate this, we provide a sample configuration for the nginx server
running as a reverse proxy to the Kea Control Agent. The server enables
authentication of the clients using certificates.
# The server certificate and key can be generated as follows:
#
# openssl genrsa -des3 -out kea-proxy.key 4096
# openssl req -new -x509 -days 365 -key kea-proxy.key -out kea-proxy.crt
#
# The CA certificate and key can be generated as follows:
#
# openssl genrsa -des3 -out ca.key 4096
# openssl req -new -x509 -days 365 -key ca.key -out ca.crt
#
#
# The client certificate needs to be generated and signed:
#
# openssl genrsa -des3 -out kea-client.key 4096
# openssl req -new -key kea-client.key -out kea-client.csr
# openssl x509 -req -days 365 -in kea-client.csr -CA ca.crt \
# -CAkey ca.key -set_serial 01 -out kea-client.crt
#
# Note that the 'common name' value used when generating the client
# and the server certificates must differ from the value used
# for the CA certificate.
#
# The client certificate must be deployed on the client system.
# In order to test the proxy configuration with 'curl' run
# command similar to the following:
#
# curl -k --key kea-client.key --cert kea-client.crt -X POST \
# -H Content-Type:application/json -d '{ "command": "list-commands" }' \
# https://kea.example.org/kea
#
#
#
# nginx configuration starts here.
events {
}
http {
# HTTPS server
server {
# Use default HTTPS port.
listen 443 ssl;
# Set server name.
server_name kea.example.org;
# Server certificate and key.
ssl_certificate /path/to/kea-proxy.crt;
ssl_certificate_key /path/to/kea-proxy.key;
# Certificate Authority. Client certificate must be signed by the CA.
ssl_client_certificate /path/to/ca.crt;
# Enable verification of the client certificate.
ssl_verify_client on;
# For URLs such as https://kea.example.org/kea, forward the
# requests to http://127.0.0.1:8080.
location /kea {
proxy_pass http://127.0.0.1:8080;
}
}
}
Note
Note that the configuration snippet provided above is for testing purposes
only. Consult security policies and best practices of your organization
which apply to this setup.
When you use an HTTP client without TLS support as kea-shell you can use
an HTTP/HTTPS translator such as stunnel in client mode. A sample
configuration is provided in the doc/examples/https/shell/ directory
7.4. Control Agent Limitations
Control Agent is a new component, first released in Kea 1.2. In this
release it comes with one notable limitation:
* keactrl hasn't been updated to manage the Control Agent (start, stop
reload). As a result, the CA must be started directly as described in
Section 7.5, "Starting Control Agent"
7.5. Starting Control Agent
The CA is started by running its binary and specifying the configuration
file it should use. For example:
$ ./kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf
7.6. Connecting to the Control Agent
For an example of tool that can take advantage of the RESTful API, see
Chapter 19, The Kea Shell.
Chapter 8. The DHCPv4 Server
Table of Contents
8.1. Starting and Stopping the DHCPv4 Server
8.2. DHCPv4 Server Configuration
8.2.1. Introduction
8.2.2. Lease Storage
8.2.3. Hosts Storage
8.2.4. Interface Configuration
8.2.5. Issues with Unicast Responses to DHCPINFORM
8.2.6. IPv4 Subnet Identifier
8.2.7. Configuration of IPv4 Address Pools
8.2.8. Standard DHCPv4 Options
8.2.9. Custom DHCPv4 options
8.2.10. DHCPv4 Private Options
8.2.11. DHCPv4 Vendor Specific Options
8.2.12. Nested DHCPv4 Options (Custom Option Spaces)
8.2.13. Unspecified Parameters for DHCPv4 Option
Configuration
8.2.14. Stateless Configuration of DHCPv4 Clients
8.2.15. Client Classification in DHCPv4
8.2.16. DDNS for DHCPv4
8.2.17. Next Server (siaddr)
8.2.18. Echoing Client-ID (RFC 6842)
8.2.19. Using Client Identifier and Hardware Address
8.2.20. DHCPv4-over-DHCPv6: DHCPv4 Side
8.3. Host Reservation in DHCPv4
8.3.1. Address Reservation Types
8.3.2. Conflicts in DHCPv4 Reservations
8.3.3. Reserving a Hostname
8.3.4. Including Specific DHCPv4 Options in Reservations
8.3.5. Reserving Next Server, Server Hostname and Boot File
Name
8.3.6. Reserving Client Classes in DHCPv4
8.3.7. Storing Host Reservations in MySQL, PostgreSQL or
Cassandra
8.3.8. Fine Tuning DHCPv4 Host Reservation
8.4. Shared networks in DHCPv4
8.4.1. Local and relayed traffic in shared networks
8.4.2. Client classification in shared networks
8.4.3. Host reservations in shared networks
8.5. Server Identifier in DHCPv4
8.6. How the DHCPv4 Server Selects a Subnet for the Client
8.6.1. Using a Specific Relay Agent for a Subnet
8.6.2. Segregating IPv4 Clients in a Cable Network
8.7. Duplicate Addresses (DHCPDECLINE Support)
8.8. Statistics in the DHCPv4 Server
8.9. Management API for the DHCPv4 Server
8.10. Supported DHCP Standards
8.11. User contexts in IPv4
8.12. DHCPv4 Server Limitations
8.13. Kea DHCPv4 server examples
8.1. Starting and Stopping the DHCPv4 Server
It is recommended that the Kea DHCPv4 server be started and stopped using
keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
is also possible to run the server directly: it accepts the following
command-line switches:
* -c file - specifies the configuration file. This is the only mandatory
switch.
* -d - specifies whether the server logging should be switched to
debug/verbose mode. In verbose mode, the logging severity and
debuglevel specified in the configuration file are ignored and "debug"
severity and the maximum debuglevel (99) are assumed. The flag is
convenient, for temporarily switching the server into maximum
verbosity, e.g. when debugging.
* -p port - specifies UDP port on which the server will listen. This is
only useful during testing, as a DHCPv4 server listening on ports
other than the standard ones will not be able to handle regular DHCPv4
queries.
* -t file - specifies the configuration file to be tested. Kea-dhcp4
will attempt to load it, and will conduct sanity checks. Note that
certain checks are possible only while running the actual server. The
actual status is reported with exit code (0 = configuration looks ok,
1 = error encountered). Kea will print out log messages to standard
output and error to standard error when testing configuration.
* -v - prints out the Kea version and exits.
* -V - prints out the Kea extended version with additional parameters
and exits. The listing includes the versions of the libraries
dynamically linked to Kea.
* -W - prints out the Kea configuration report and exits. The report is
a copy of the config.report file produced by ./configure: it is
embedded in the executable binary.
The config.report may also be accessed more directly. The following
command may be used to extract this information. The binary path may be
found in the install directory or in the .libs subdirectory in the source
tree. For example kea/src/bin/dhcp4/.libs/kea-dhcp4.
strings path/kea-dhcp4 | sed -n 's/;;;; //p'
On start-up, the server will detect available network interfaces and will
attempt to open UDP sockets on all interfaces mentioned in the
configuration file. Since the DHCPv4 server opens privileged ports, it
requires root access. Make sure you run this daemon as root.
During startup the server will attempt to create a PID file of the form:
localstatedir]/[conf name].kea-dhcp6.pid where:
* localstatedir: The value as passed into the build configure script. It
defaults to "/usr/local/var". (Note that this value may be overridden
at run time by setting the environment variable KEA_PIDFILE_DIR. This
is intended primarily for testing purposes.)
* conf name: The configuration file name used to start the server, minus
all preceding path and file extension. For example, given a pathname
of "/usr/local/etc/kea/myconf.txt", the portion used would be
"myconf".
If the file already exists and contains the PID of a live process, the
server will issue a DHCP4_ALREADY_RUNNING log message and exit. It is
possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
The server can be stopped using the kill command. When running in a
console, the server can also be shut down by pressing ctrl-c. It detects
the key combination and shuts down gracefully.
8.2. DHCPv4 Server Configuration
8.2.1. Introduction
This section explains how to configure the DHCPv4 server using the Kea
configuration backend. (Kea configuration using any other backends is
outside of scope of this document.) Before DHCPv4 is started, its
configuration file has to be created. The basic configuration is as
follows:
{
# DHCPv4 configuration starts in this line
"Dhcp4": {
# First we set up global values
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
# Next we setup the interfaces to be used by the server.
"interfaces-config": {
"interfaces": [ "eth0" ]
},
# And we specify the type of lease database
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/var/kea/dhcp4.leases"
},
# Finally, we list the subnets from which we will be leasing addresses.
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{
"pool": "192.0.2.1 - 192.0.2.200"
}
]
}
]
# DHCPv4 configuration ends with the next line
}
}
The following paragraphs provide a brief overview of the parameters in the
above example together with their format. Subsequent sections of this
chapter go into much greater detail for these and other parameters.
The lines starting with a hash (#) are comments and are ignored by the
server; they do not impact its operation in any way.
The configuration starts in the first line with the initial opening curly
bracket (or brace). Each configuration consists of one or more objects. In
this specific example, we have only one object, called Dhcp4. This is a
simplified configuration, as usually there will be additional objects,
like Logging or DhcpDdns, but we omit them now for clarity. The Dhcp4
configuration starts with the "Dhcp4": { line and ends with the
corresponding closing brace (in the above example, the brace after the
last comment). Everything defined between those lines is considered to be
the Dhcp4 configuration.
In the general case, the order in which those parameters appear does not
matter. There are two caveats here though. The first one is to remember
that the configuration file must be well formed JSON. That means that the
parameters for any given scope must be separated by a comma and there must
not be a comma after the last parameter. When reordering a configuration
file, keep in mind that moving a parameter to or from the last position in
a given scope may also require moving the comma. The second caveat is that
it is uncommon -- although legal JSON -- to repeat the same parameter
multiple times. If that happens, the last occurrence of a given parameter
in a given scope is used while all previous instances are ignored. This is
unlikely to cause any confusion as there are no real life reasons to keep
multiple copies of the same parameter in your configuration file.
Moving onto the DHCPv4 configuration elements, the first few elements
define some global parameters. valid-lifetime defines how long the
addresses (leases) given out by the server are valid. If nothing changes,
a client that got an address is allowed to use it for 4000 seconds. (Note
that integer numbers are specified as is, without any quotes around them.)
renew-timer and rebind-timer are values (also in seconds) that define T1
and T2 timers that govern when the client will begin the renewal and
rebind procedures.
Note
Both renew-timer and rebind-timer are optional. The server will only send
rebind-timer to the client, via DHPv4 option code 59, if it is less than
valid-lifetime; and it will only send renew-timer, via DHCPv4 option code
58, if it is less than rebind-timer (or valid-lifetime if rebind-timer was
not specified). In their absence, the client should select values for T1
and T2 timers according to the RFC 2131.
The interfaces-config map specifies the server configuration concerning
the network interfaces, on which the server should listen to the DHCP
messages. The interfaces parameter specifies a list of network interfaces
on which the server should listen. Lists are opened and closed with square
brackets, with elements separated by commas. Had we wanted to listen on
two interfaces, the interfaces-config would look like this:
"interfaces-config": {
"interfaces": [ "eth0", "eth1" ]
},
The next couple of lines define the lease database, the place where the
server stores its lease information. This particular example tells the
server to use memfile, which is the simplest (and fastest) database
backend. It uses an in-memory database and stores leases on disk in a CSV
file. This is a very simple configuration. Usually the lease database
configuration is more extensive and contains additional parameters. Note
that lease-database is an object and opens up a new scope, using an
opening brace. Its parameters (just one in this example - type) follow.
Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters for the Dhcp4
definition follow, a trailing comma is present.
Finally, we need to define a list of IPv4 subnets. This is the most
important DHCPv4 configuration structure as the server uses that
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
specified with the subnet4 parameter. It is a list, so it starts and ends
with square brackets. Each subnet definition in the list has several
attributes associated with it, so it is a structure and is opened and
closed with braces. At a minimum, a subnet definition has to have at least
two parameters: subnet (that defines the whole subnet) and pools (which is
a list of dynamically allocated pools that are governed by the DHCP
server).
The example contains a single subnet. Had more than one been defined,
additional elements in the subnet4 parameter would be specified and
separated by commas. For example, to define three subnets, the following
syntax would be used:
"subnet4": [
{
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
"subnet": "192.0.2.0/24"
},
{
"pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
"subnet": "192.0.3.0/24"
},
{
"pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
"subnet": "192.0.4.0/24"
}
]
Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
After all the parameters have been specified, we have two contexts open:
global and Dhcp4, hence we need two closing curly brackets to close them.
In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
be followed by a comma and another object definition.
8.2.2. Lease Storage
All leases issued by the server are stored in the lease database.
Currently there are four database backends available: memfile (which is
the default backend), MySQL, PostgreSQL and Cassandra.
8.2.2.1. Memfile - Basic Storage for Leases
The server is able to store lease data in different repositories. Larger
deployments may elect to store leases in a database. Section 8.2.2.2,
"Lease Database Configuration" describes this option. In typical smaller
deployments though, the server will store lease information in a CSV file
rather than a database. As well as requiring less administration, an
advantage of using a file for storage is that it eliminates a dependency
on third-party database software.
The configuration of the file backend (Memfile) is controlled through the
Dhcp4/lease-database parameters. The type parameter is mandatory and it
specifies which storage for leases the server should use. The value of
"memfile" indicates that the file should be used as the storage. The
following list gives additional, optional, parameters that can be used to
configure the Memfile backend.
* persist: controls whether the new leases and updates to existing
leases are written to the file. It is strongly recommended that the
value of this parameter is set to true at all times, during the
server's normal operation. Not writing leases to disk will mean that
if a server is restarted (e.g. after a power failure), it will not
know what addresses have been assigned. As a result, it may hand out
addresses to new clients that are already in use. The value of false
is mostly useful for performance testing purposes. The default value
of the persist parameter is true, which enables writing lease updates
to the lease file.
* name: specifies an absolute location of the lease file in which new
leases and lease updates will be recorded. The default value for this
parameter is "[kea-install-dir]/var/kea/kea-leases4.csv" .
* lfc-interval: specifies the interval in seconds, at which the server
will perform a lease file cleanup (LFC). This removes redundant
(historical) information from the lease file and effectively reduces
the lease file size. The cleanup process is described in more detailed
fashion further in this section. The default value of the lfc-interval
is 3600. A value of 0 disables the LFC.
An example configuration of the Memfile backend is presented below:
"Dhcp4": {
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/tmp/kea-leases4.csv",
"lfc-interval": 1800
}
}
This configuration selects the /tmp/kea-leases4.csv as the storage for
lease information and enables persistence (writing lease updates to this
file). It also configures the backend perform the periodic cleanup of the
lease files, executed every 30 minutes.
It is important to know how the lease file contents are organized to
understand why the periodic lease file cleanup is needed. Every time the
server updates a lease or creates a new lease for the client, the new
lease information must be recorded in the lease file. For performance
reasons, the server does not update the existing client's lease in the
file, as it would potentially require rewriting the entire file. Instead,
it simply appends the new lease information to the end of the file: the
previous lease entries for the client are not removed. When the server
loads leases from the lease file, e.g. at the server startup, it assumes
that the latest lease entry for the client is the valid one. The previous
entries are discarded. This means that the server can re-construct the
accurate information about the leases even though there may be many lease
entries for each client. However, storing many entries for each client
results in bloated lease file and impairs the performance of the server's
startup and reconfiguration as it needs to process a larger number of
lease entries.
Lease file cleanup (LFC) removes all previous entries for each client and
leaves only the latest ones. The interval at which the cleanup is
performed is configurable, and it should be selected according to the
frequency of lease renewals initiated by the clients. The more frequent
the renewals, the smaller the value of lfc-interval should be. Note
however, that the LFC takes time and thus it is possible (although
unlikely) that new cleanup is started while the previous cleanup instance
is still running, if the lfc-interval is too short. The server would
recover from this by skipping the new cleanup when it detects that the
previous cleanup is still in progress. But it implies that the actual
cleanups will be triggered more rarely than configured. Moreover,
triggering a new cleanup adds an overhead to the server which will not be
able to respond to new requests for a short period of time when the new
cleanup process is spawned. Therefore, it is recommended that the
lfc-interval value is selected in a way that would allow for the LFC to
complete the cleanup before a new cleanup is triggered.
Lease file cleanup is performed by a separate process (in background) to
avoid a performance impact on the server process. In order to avoid the
conflicts between two processes both using the same lease files, the LFC
process operates on the copy of the original lease file, rather than on
the lease file used by the server to record lease updates. There are also
other files being created as a side effect of the lease file cleanup. The
detailed description of the LFC is located on the Kea wiki:
http://kea.isc.org/wiki/LFCDesign.
8.2.2.2. Lease Database Configuration
Note
Lease database access information must be configured for the DHCPv4
server, even if it has already been configured for the DHCPv6 server. The
servers store their information independently, so each server can use a
separate database or both servers can use the same database.
Lease database configuration is controlled through the
Dhcp4/lease-database parameters. The type of the database must be set to
"memfile", "mysql", "postgresql" or "cql", e.g.
"Dhcp4": { "lease-database": { "type": "mysql", ... }, ... }
Next, the name of the database to hold the leases must be set: this is the
name used when the database was created (see Section 4.3.2.1, "First Time
Creation of the MySQL Database", Section 4.3.3.1, "First Time Creation of
the PostgreSQL Database" or Section 4.3.4.1, "First Time Creation of the
Cassandra Database").
"Dhcp4": { "lease-database": { "name": "database-name" , ... }, ... }
For Cassandra:
"Dhcp4": { "lease-database": { "keyspace": "database-name" , ... }, ... }
If the database is located on a different system to the DHCPv4 server, the
database host name must also be specified. (It should be noted that this
configuration may have a severe impact on server performance.):
"Dhcp4": { "lease-database": { "host": "remote-host-name", ... }, ... }
The usual state of affairs will be to have the database on the same
machine as the DHCPv4 server. In this case, set the value to the empty
string:
"Dhcp4": { "lease-database": { "host" : "", ... }, ... }
Should the database use a port different than default, it may be specified
as well:
"Dhcp4": { "lease-database": { "port" : 12345, ... }, ... }
Should the database be located on a different system, you may need to
specify a longer interval for the connection timeout:
"Dhcp4": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }
The default value of five seconds should be more than adequate for local
connections. If a timeout is given though, it should be an integer greater
than zero.
The maxiumum number of times the server will automatically attempt to
reconnect to the lease database after connectivity has been lost may be
specified:
"Dhcp4": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
If the server is unable to reconnect to the database after making the
maximum number of attempts the server will exit. A value of zero (the
default) disables automatic recovery and the server will exit immediately
upon detecting a loss of connectivity (MySQL and Postgres only).
The number of seconds the server will wait in between attempts to
reconnect to the lease database after connectivity has been lost may also
be specified:
"Dhcp4": { "lease-database": { "reconnect-wait-time" : number-of-seconds, ... }, ... }
A value of zero (the default) disables automatic recovery and the server
will exit immediately upon detecting a loss of connectivity (MySQL and
Postgres only).
Finally, the credentials of the account under which the server will access
the database should be set:
"Dhcp4": { "lease-database": { "user": "user-name",
"password": "password",
... },
... }
If there is no password to the account, set the password to the empty
string "". (This is also the default.)
8.2.2.3. Cassandra specific parameters
Cassandra backend is configured slightly differently. Cassandra has a
concept of contact points that could be used to contact the cluster,
instead of a single IP or hostname. It takes a list of comma separated IP
addresses. This may be specified as:
"Dhcp4": {
"lease-database": {
"type": "cql",
"contact-points": "ip-address1, ip-address2 [,...]",
...
},
...
}
Cassandra also supports a number of optional parameters:
* reconnect-wait-time - governs how long Kea waits before attempting to
reconnect. Expressed in milliseconds. The default is 2000 [ms].
* connect-timeout - sets the timeout for connecting to a node. Expressed
in milliseconds. The default is 5000 [ms].
* request-timeout - this parameter sets the timeout for waiting for a
response from a node. Expressed in milliseconds. The default is 12000
[ms].
* tcp-keepalive - This parameter governs the TCP keep-alive mechanism.
Expressed in seconds of delay. If the parameter is not present, the
mechanism is disabled.
* tcp-nodelay - This parameter enables/disabled Nagle's algorithm on
connections. The default is true.
For example, a complex Cassandra configuration with most parameters
specified could look as follows:
"Dhcp4": {
"lease-database": {
"type": "cql",
"keyspace": "keatest",
"contact-points": "192.0.2.1, 192.0.2.2, 192.0.2.3",
"port": 9042,
"reconnect-wait-time": 2000,
"connect-timeout": 5000,
"request-timeout": 12000,
"tcp-keepalive": 1,
"tcp-nodelay": true
},
...
}
Similar parameters can be specified for hosts database.
8.2.3. Hosts Storage
Kea is also able to store information about host reservations in the
database. The hosts database configuration uses the same syntax as the
lease database. In fact, a Kea server opens independent connections for
each purpose, be it lease or hosts information. This arrangement gives the
most flexibility. Kea can be used to keep leases and host reservations
separately, but can also point to the same database. Currently the
supported hosts database types are MySQL, PostgreSQL and Cassandra.
Please note that usage of hosts storage is optional. A user can define all
host reservations in the configuration file. That is the recommended way
if the number of reservations is small. However, when the number of
reservations grows it's more convenient to use host storage. Please note
that both storage methods (configuration file and one of the supported
databases) can be used together. If hosts are defined in both places, the
definitions from the configuration file are checked first and external
storage is checked later, if necessary.
Version 1.4 extends the host storage to multiple storages. Operations are
performed on host storages in the configuration order with a special case
for addition: read-only storages must be configured after a required
read-write storage, or host reservation addition will always fail.
8.2.3.1. DHCPv4 Hosts Database Configuration
Hosts database configuration is controlled through the
Dhcp4/hosts-database parameters. If enabled, the type of the database must
be set to "mysql" or "postgresql". Other hosts backends may be added in
later versions of Kea.
"Dhcp4": { "hosts-database": { "type": "mysql", ... }, ... }
Next, the name of the database to hold the reservations must be set: this
is the name used when the lease database was created (see Section 4.3,
"Supported Databases" for instructions how to setup the desired database
type).
"Dhcp4": { "hosts-database": { "name": "database-name" , ... }, ... }
If the database is located on a different system than the DHCPv4 server,
the database host name must also be specified. (Again it should be noted
that this configuration may have a severe impact on server performance.):
"Dhcp4": { "hosts-database": { "host": remote-host-name, ... }, ... }
The usual state of affairs will be to have the database on the same
machine as the DHCPv4 server. In this case, set the value to the empty
string:
"Dhcp4": { "hosts-database": { "host" : "", ... }, ... }
Should the database use a port different than default, it may be specified
as well:
"Dhcp4": { "hosts-database": { "port" : 12345, ... }, ... }
The maxiumum number of times the server will automatically attempt to
reconnect to the host database after connectivity has been lost may be
specified:
"Dhcp4": { "hosts-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
If the server is unable to reconnect to the database after making the
maximum number of attempts the server will exit. A value of zero (the
default) disables automatic recovery and the server will exit immediately
upon detecting a loss of connectivity (MySQL and Postgres only).
The number of seconds the server will wait in between attempts to
reconnect to the host database after connectivity has been lost may also
be specified:
"Dhcp4": { "hosts-database": { "reconnect-wait-time" : number-of-seconds, ... }, ... }
A value of zero (the default) disables automatic recovery and the server
will exit immediately upon detecting a loss of connectivity (MySQL and
Postgres only).
Finally, the credentials of the account under which the server will access
the database should be set:
"Dhcp4": { "hosts-database": { "user": "user-name",
"password": "password",
... },
... }
If there is no password to the account, set the password to the empty
string "". (This is also the default.)
The multiple storage extension uses a similar syntax: a configuration is
placed into a "hosts-databases" list instead of into a "hosts-database"
entry as in:
"Dhcp4": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }
For additional Cassandra specific parameters, see Section 8.2.2.3,
"Cassandra specific parameters".
8.2.3.2. Using Read-Only Databases for Host Reservations
In some deployments the database user whose name is specified in the
database backend configuration may not have write privileges to the
database. This is often required by the policy within a given network to
secure the data from being unintentionally modified. In many cases
administrators have inventory databases deployed, which contain
substantially more information about the hosts than static reservations
assigned to them. The inventory database can be used to create a view of a
Kea hosts database and such view is often read only.
Kea host database backends operate with an implicit configuration to both
read from and write to the database. If the database user does not have
write access to the host database, the backend will fail to start and the
server will refuse to start (or reconfigure). However, if access to a read
only host database is required for retrieving reservations for clients
and/or assign specific addresses and options, it is possible to explicitly
configure Kea to start in "read-only" mode. This is controlled by the
readonly boolean parameter as follows:
"Dhcp4": { "hosts-database": { "readonly": true, ... }, ... }
Setting this parameter to false would configure the database backend to
operate in "read-write" mode, which is also a default configuration if the
parameter is not specified.
Note
The readonly parameter is currently only supported for MySQL and
PostgreSQL databases.
8.2.4. Interface Configuration
The DHCPv4 server has to be configured to listen on specific network
interfaces. The simplest network interface configuration tells the server
to listen on all available interfaces:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "*" ]
}
...
},
The asterisk plays the role of a wildcard and means "listen on all
interfaces". However, it is usually a good idea to explicitly specify
interface names:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ]
},
...
}
It is possible to use wildcard interface name (asterisk) concurrently with
explicit interface names:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3", "*" ]
},
...
}
It is anticipated that this form of usage will only be used when it is
desired to temporarily override a list of interface names and listen on
all interfaces.
Some deployments of DHCP servers require that the servers listen on the
interfaces with multiple IPv4 addresses configured. In these situations,
the address to use can be selected by appending an IPv4 address to the
interface name in the following manner:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]
},
...
}
Should the server be required to listen on multiple IPv4 addresses
assigned to the same interface, multiple addresses can be specified for an
interface as in the example below:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1/10.0.0.1", "eth1/10.0.0.2" ]
},
...
}
Alternatively, if the server should listen on all addresses for the
particular interface, an interface name without any address should be
specified.
Kea supports responding to directly connected clients which don't have an
address configured. This requires that the server injects the hardware
address of the destination into the data link layer of the packet being
sent to the client. The DHCPv4 server utilizes the raw sockets to achieve
this, and builds the entire IP/UDP stack for the outgoing packets. The
down side of raw socket use, however, is that incoming and outgoing
packets bypass the firewalls (e.g. iptables). It is also troublesome to
handle traffic on multiple IPv4 addresses assigned to the same interface,
as raw sockets are bound to the interface and advanced packet filtering
techniques (e.g. using the BPF) have to be used to receive unicast traffic
on the desired addresses assigned to the interface, rather than capturing
whole traffic reaching the interface to which the raw socket is bound.
Therefore, in the deployments where the server doesn't have to provision
the directly connected clients and only receives the unicast packets from
the relay agents, the DHCP server should be configured to utilize IP/UDP
datagram sockets instead of raw sockets. The following configuration
demonstrates how this can be achieved:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ],
"dhcp-socket-type": "udp"
},
...
}
The dhcp-socket-type specifies that the IP/UDP sockets will be opened on
all interfaces on which the server listens, i.e. "eth1" and "eth3" in our
case. If the dhcp-socket-type is set to raw, it configures the server to
use raw sockets instead. If the dhcp-socket-type value is not specified,
the default value raw is used.
Using UDP sockets automatically disables the reception of broadcast
packets from directly connected clients. This effectively means that the
UDP sockets can be used for relayed traffic only. When using the raw
sockets, both the traffic from the directly connected clients and the
relayed traffic will be handled. Caution should be taken when configuring
the server to open multiple raw sockets on the interface with several IPv4
addresses assigned. If the directly connected client sends the message to
the broadcast address all sockets on this link will receive this message
and multiple responses will be sent to the client. Hence, the
configuration with multiple IPv4 addresses assigned to the interface
should not be used when the directly connected clients are operating on
that link. To use a single address on such interface, the
"interface-name/address" notation should be used.
Note
Specifying the value raw as the socket type, doesn't guarantee that the
raw sockets will be used! The use of raw sockets to handle the traffic
from the directly connected clients is currently supported on Linux and
BSD systems only. If the raw sockets are not supported on the particular
OS, the server will issue a warning and fall back to use IP/UDP sockets.
In typical environment the DHCP server is expected to send back a response
on the same network interface on which the query is received. This is the
default behavior. However, in some deployments it is desired that the
outbound (response) packets will be sent as regular traffic and the
outbound interface will be determined by the routing tables. This kind of
asymetric traffic is uncommon, but valid. Kea now supports a parameter
called outbound-interface that controls this behavior. It supports two
values. The first one, same-as-inbound, tells Kea to send back the
response on the same inteface the query packet is received. This is the
default behavior. The second one, use-routing tells Kea to send regular
UDP packets and let the kernel's routing table to determine most
appropriate interface. This only works when dhcp-socket-type is set to
udp. An example configuration looks as follows:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ],
"dhcp-socket-type": "udp",
"outbound-interface": "use-routing"
},
...
}
Interfaces are re-detected at each reconfiguration. This behavior can be
disabled by setting re-detect value to false, for instance:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ],
"re-detect": false
},
...
}
Note interfaces are not re-detected during config-test.
Usually loopback interfaces (e.g. the "lo" or "lo0" interface) may not be
configured but if a loopback interface is explicitely configured and
IP/UDP sockets are specified the loopback interface is accepted.
It can be used for instance to run Kea in a FreeBSD jail having only a
loopback interface, servicing relayed DHCP request:
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "lo0" ],
"dhcp-socket-type": "udp"
},
...
}
8.2.5. Issues with Unicast Responses to DHCPINFORM
The use of UDP sockets has certain benefits in deployments where the
server receives only relayed traffic; these benefits are mentioned in
Section 8.2.4, "Interface Configuration". From the administrator's
perspective it is often desirable to configure the system's firewall to
filter out the unwanted traffic, and the use of UDP sockets facilitates
this. However, the administrator must also be aware of the implications
related to filtering certain types of traffic as it may impair the DHCP
server's operation.
In this section we are focusing on the case when the server receives the
DHCPINFORM message from the client via a relay. According to RFC 2131, the
server should unicast the DHCPACK response to the address carried in the
"ciaddr" field. When the UDP socket is in use, the DHCP server relies on
the low level functions of an operating system to build the data link, IP
and UDP layers of the outgoing message. Typically, the OS will first use
ARP to obtain the client's link layer address to be inserted into the
frame's header, if the address is not cached from a previous transaction
that the client had with the server. When the ARP exchange is successful,
the DHCP message can be unicast to the client, using the obtained address.
Some system administrators block ARP messages in their network, which
causes issues for the server when it responds to the DHCPINFORM messages,
because the server is unable to send the DHCPACK if the preceding ARP
communication fails. Since the OS is entirely responsible for the ARP
communication and then sending the DHCP packet over the wire, the DHCP
server has no means to determine that the ARP exchange failed and the DHCP
response message was dropped. Thus, the server does not log any error
messages when the outgoing DHCP response is dropped. At the same time, all
hooks pertaining to the packet sending operation will be called, even
though the message never reaches its destination.
Note that the issue described in this section is not observed when the raw
sockets are in use, because, in this case, the DHCP server builds all the
layers of the outgoing message on its own and does not use ARP. Instead,
it inserts the value carried in the 'chaddr' field of the DHCPINFORM
message into the link layer.
Server administrators willing to support DHCPINFORM messages via relays
should not block ARP traffic in their networks or should use raw sockets
instead of UDP sockets.
8.2.6. IPv4 Subnet Identifier
The subnet identifier is a unique number associated with a particular
subnet. In principle, it is used to associate clients' leases with their
respective subnets. When a subnet identifier is not specified for a subnet
being configured, it will be automatically assigned by the configuration
mechanism. The identifiers are assigned from 1 and are monotonically
increased for each subsequent subnet: 1, 2, 3 ....
If there are multiple subnets configured with auto-generated identifiers
and one of them is removed, the subnet identifiers may be renumbered. For
example: if there are four subnets and the third is removed the last
subnet will be assigned the identifier that the third subnet had before
removal. As a result, the leases stored in the lease database for subnet 3
are now associated with subnet 4, something that may have unexpected
consequences. It is planned to implement a mechanism to preserve
auto-generated subnet ids in a future version of Kea. However, the only
remedy for this issue at present is to manually specify a unique
identifier for each subnet.
The following configuration will assign the specified subnet identifier to
the newly configured subnet:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"id": 1024,
...
}
]
}
This identifier will not change for this subnet unless the "id" parameter
is removed or set to 0. The value of 0 forces auto-generation of the
subnet identifier.
8.2.7. Configuration of IPv4 Address Pools
The main role of a DHCPv4 server is address assignment. For this, the
server has to be configured with at least one subnet and one pool of
dynamic addresses for it to manage. For example, assume that the server is
connected to a network segment that uses the 192.0.2.0/24 prefix. The
Administrator of that network has decided that addresses from range
192.0.2.10 to 192.0.2.20 are going to be managed by the Dhcp4 server. Such
a configuration can be achieved in the following way:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{ "pool": "192.0.2.10 - 192.0.2.20" }
],
...
}
]
}
Note that subnet is defined as a simple string, but the pools parameter is
actually a list of pools: for this reason, the pool definition is enclosed
in square brackets, even though only one range of addresses is specified.
Each pool is a structure that contains the parameters that describe a
single pool. Currently there is only one parameter, pool, which gives the
range of addresses in the pool. Additional parameters will be added in
future releases of Kea.
It is possible to define more than one pool in a subnet: continuing the
previous example, further assume that 192.0.2.64/26 should be also be
managed by the server. It could be written as 192.0.2.64 to 192.0.2.127.
Alternatively, it can be expressed more simply as 192.0.2.64/26. Both
formats are supported by Dhcp4 and can be mixed in the pool list. For
example, one could define the following pools:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{ "pool": "192.0.2.10-192.0.2.20" },
{ "pool": "192.0.2.64/26" }
],
...
}
],
...
}
White space in pool definitions is ignored, so spaces before and after the
hyphen are optional. They can be used to improve readability.
The number of pools is not limited, but for performance reasons it is
recommended to use as few as possible.
The server may be configured to serve more than one subnet:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
...
},
{
"subnet": "192.0.3.0/24",
"pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
...
},
{
"subnet": "192.0.4.0/24",
"pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
...
}
]
}
When configuring a DHCPv4 server using prefix/length notation, please pay
attention to the boundary values. When specifying that the server can use
a given pool, it will also be able to allocate the first (typically
network address) and the last (typically broadcast address) address from
that pool. In the aforementioned example of pool 192.0.3.0/24, both
192.0.3.0 and 192.0.3.255 addresses may be assigned as well. This may be
invalid in some network configurations. If you want to avoid this, please
use the "min-max" notation.
8.2.8. Standard DHCPv4 Options
One of the major features of the DHCPv4 server is to provide configuration
options to clients. Most of the options are sent by the server only if the
client explicitly requests them using the Parameter Request List option.
Those that do not require inclusion in the Parameter Request List option
are commonly used options, e.g. "Domain Server", and options which require
special behavior, e.g. "Client FQDN" is returned to the client if the
client has included this option in its message to the server.
Table 8.1, "List of standard DHCPv4 options" comprises the list of the
standard DHCPv4 options whose values can be configured using the
configuration structures described in this section. This table excludes
the options which require special processing and thus cannot be configured
with some fixed values. The last column of the table indicates which
options can be sent by the server even when they are not requested in the
Parameter Request list option, and those which are sent only when
explicitly requested.
The following example shows how to configure the addresses of DNS servers,
which is one of the most frequently used options. Options specified in
this way are considered global and apply to all configured subnets.
"Dhcp4": {
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
},
...
]
}
Note that only one of name or code is required, you don't need to specify
both. Space has a default value of "dhcp4", so you can skip this as well
if you define a regular (not encapsulated) DHCPv4 option. Finally,
csv-format defaults to true, so it too can be skipped, unless you want to
specify the option value as hexstring. Therefore the above example can be
simplified to:
"Dhcp4": {
"option-data": [
{
"name": "domain-name-servers",
"data": "192.0.2.1, 192.0.2.2"
},
...
]
}
Defined options are added to response when the client requests them at a
few exceptions which are always added. To enforce the addition of a
particular option set the always-send flag to true as in:
"Dhcp4": {
"option-data": [
{
"name": "domain-name-servers",
"data": "192.0.2.1, 192.0.2.2",
"always-send": true
},
...
]
}
The effect is the same as if the client added the option code in the
Parameter Request List option (or its equivalent for vendor options) so
in:
"Dhcp4": {
"option-data": [
{
"name": "domain-name-servers",
"data": "192.0.2.1, 192.0.2.2",
"always-send": true
},
...
],
"subnet4": [
{
"subnet": "192.0.3.0/24",
"option-data": [
{
"name": "domain-name-servers",
"data": "192.0.3.1, 192.0.3.2"
},
...
],
...
},
...
],
...
}
The Domain Name Servers option is always added to responses (the
always-send is "sticky") but the value is the subnet one when the client
is localized in the subnet.
The name parameter specifies the option name. For a list of currently
supported names, see Table 8.1, "List of standard DHCPv4 options" below.
The code parameter specifies the option code, which must match one of the
values from that list. The next line specifies the option space, which
must always be set to "dhcp4" as these are standard DHCPv4 options. For
other option spaces, including custom option spaces, see Section 8.2.12,
"Nested DHCPv4 Options (Custom Option Spaces)". The next line specifies
the format in which the data will be entered: use of CSV (comma separated
values) is recommended. The sixth line gives the actual value to be sent
to clients. Data is specified as normal text, with values separated by
commas if more than one value is allowed.
Options can also be configured as hexadecimal values. If csv-format is set
to false, option data must be specified as a hexadecimal string. The
following commands configure the domain-name-servers option for all
subnets with the following addresses: 192.0.3.1 and 192.0.3.2. Note that
csv-format is set to false.
"Dhcp4": {
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": false,
"data": "C0 00 03 01 C0 00 03 02"
},
...
],
...
}
Care should be taken to use proper encoding when using hexadecimal format
as Kea's ability to validate data correctness in hexadecimal is limited.
Most of the parameters in the "option-data" structure are optional and can
be omitted in some circumstances as discussed in the Section 8.2.13,
"Unspecified Parameters for DHCPv4 Option Configuration".
It is possible to specify or override options on a per-subnet basis. If
clients connected to most of your subnets are expected to get the same
values of a given option, you should use global options: you can then
override specific values for a small number of subnets. On the other hand,
if you use different values in each subnet, it does not make sense to
specify global option values (Dhcp4/option-data), rather you should set
only subnet-specific values (Dhcp4/subnet[X]/option-data[Y]).
The following commands override the global DNS servers option for a
particular subnet, setting a single DNS server with address 192.0.2.3.
"Dhcp4": {
"subnet4": [
{
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.3"
},
...
],
...
},
...
],
...
}
In some cases it is useful to associate some options with an address pool
from which a client is assigned a lease. Pool specific option values
override subnet specific and global option values. The server's
administrator must not try to prioritize assignment of pool specific
options by trying to order pools declarations in the server configuration.
Future Kea releases may change the order in which options are assigned
from the pools without any notice.
The following configuration snippet demonstrates how to specify the DNS
servers option, which will be assigned to a client only if the client
obtains an address from the given pool:
"Dhcp4": {
"subnet4": [
{
"pools": [
{
"pool": "192.0.2.1 - 192.0.2.200",
"option-data": [
{
"name": "domain-name-servers",
"data": "192.0.2.3"
},
...
],
...
},
...
],
...
},
...
],
...
}
Options can be specified also in class of host reservation scope. In Kea
1.4 options precedence order is (from most important): host reservation,
pool, subnet, shared network, class, global. In Kea 1.5 order will be
changed to: host reservation, class, pool, subnet, shared network, global
OR it will be fully configurable.
The currently supported standard DHCPv4 options are listed in Table 8.1,
"List of standard DHCPv4 options". The "Name" and "Code" are the values
that should be used as a name in the option-data structures. "Type"
designates the format of the data: the meanings of the various types is
given in Table 8.2, "List of standard DHCP option types".
When a data field is a string, and that string contains the comma (,;
U+002C) character, the comma must be escaped with a double reverse solidus
character (\; U+005C). This double escape is required, because both the
routine splitting CSV data into fields and JSON use the same escape
character: a single escape (\,) would make the JSON invalid. For example,
the string "foo,bar" would be represented as:
"Dhcp4": {
"subnet4": [
{
"pools": [
{
"option-data": [
{
"name": "boot-file-name",
"data": "foo\\,bar"
}
]
},
...
],
...
},
...
],
...
}
Some options are designated as arrays, which means that more than one
value is allowed in such an option. For example the option time-servers
allows the specification of more than one IPv4 address, so allowing
clients to obtain the addresses of multiple NTP servers.
The Section 8.2.9, "Custom DHCPv4 options" describes the configuration
syntax to create custom option definitions (formats). It is generally not
allowed to create custom definitions for standard options, even if the
definition being created matches the actual option format defined in the
RFCs. There is an exception from this rule for standard options for which
Kea currently does not provide a definition. In order to use such options,
a server administrator must create a definition as described in
Section 8.2.9, "Custom DHCPv4 options" in the 'dhcp4' option space. This
definition should match the option format described in the relevant RFC
but the configuration mechanism will allow any option format as it
presently has no means to validate it.
Table 8.1. List of standard DHCPv4 options
+-------------------------------------------------------------------------------------+
| | | | |Returned if|
| Name |Code| Type |Array?| not |
| | | | |requested? |
|--------------------------------------+----+----------------------+------+-----------|
|time-offset | 2 | int32 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|routers | 3 | ipv4-address | true | true |
|--------------------------------------+----+----------------------+------+-----------|
|time-servers | 4 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|name-servers | 5 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|domain-name-servers | 6 | ipv4-address | true | true |
|--------------------------------------+----+----------------------+------+-----------|
|log-servers | 7 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|cookie-servers | 8 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|lpr-servers | 9 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|impress-servers | 10 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|resource-location-servers | 11 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|boot-size | 13 | uint16 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|merit-dump | 14 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|domain-name | 15 | fqdn |false | true |
|--------------------------------------+----+----------------------+------+-----------|
|swap-server | 16 | ipv4-address |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|root-path | 17 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|extensions-path | 18 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|ip-forwarding | 19 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|non-local-source-routing | 20 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|policy-filter | 21 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|max-dgram-reassembly | 22 | uint16 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|default-ip-ttl | 23 | uint8 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|path-mtu-aging-timeout | 24 | uint32 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|path-mtu-plateau-table | 25 | uint16 | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|interface-mtu | 26 | uint16 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|all-subnets-local | 27 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|broadcast-address | 28 | ipv4-address |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|perform-mask-discovery | 29 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|mask-supplier | 30 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|router-discovery | 31 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|router-solicitation-address | 32 | ipv4-address |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|static-routes | 33 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|trailer-encapsulation | 34 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|arp-cache-timeout | 35 | uint32 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|ieee802-3-encapsulation | 36 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|default-tcp-ttl | 37 | uint8 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|tcp-keepalive-interval | 38 | uint32 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|tcp-keepalive-garbage | 39 | boolean |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nis-domain | 40 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nis-servers | 41 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|ntp-servers | 42 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|vendor-encapsulated-options | 43 | empty |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-name-servers | 44 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-dd-server | 45 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-node-type | 46 | uint8 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-scope | 47 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|font-servers | 48 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|x-display-manager | 49 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-option-overload | 52 | uint8 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-server-identifier | 54 | ipv4-address |false | true |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-message | 56 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-max-message-size | 57 | uint16 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|vendor-class-identifier | 60 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nwip-domain-name | 62 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nwip-suboptions | 63 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nisplus-domain-name | 64 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nisplus-servers | 65 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|tftp-server-name | 66 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|boot-file-name | 67 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|mobile-ip-home-agent | 68 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|smtp-server | 69 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|pop-server | 70 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|nntp-server | 71 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|www-server | 72 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|finger-server | 73 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|irc-server | 74 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|streettalk-server | 75 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|streettalk-directory-assistance-server| 76 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|user-class | 77 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|slp-directory-agent | 78 | record (boolean, | true | false |
| | | ipv4-address) | | |
|--------------------------------------+----+----------------------+------+-----------|
|slp-service-scope | 79 | record (boolean, |false | false |
| | | string) | | |
|--------------------------------------+----+----------------------+------+-----------|
|nds-server | 85 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|nds-tree-name | 86 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|nds-context | 87 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|bcms-controller-names | 88 | fqdn | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|bcms-controller-address | 89 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|client-system | 93 | uint16 | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|client-ndi | 94 |record (uint8, uint8, |false | false |
| | | uint8) | | |
|--------------------------------------+----+----------------------+------+-----------|
|uuid-guid | 97 | record (uint8, hex) |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|uap-servers | 98 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|geoconf-civic | 99 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|pcode |100 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|tcode |101 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|netinfo-server-address |112 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|netinfo-server-tag |113 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|default-url |114 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|auto-config |116 | uint8 |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|name-service-search |117 | uint16 | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|subnet-selection |118 | ipv4-address |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|domain-search |119 | fqdn | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|vivco-suboptions |124 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|vivso-suboptions |125 | hex |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|pana-agent |136 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|v4-lost |137 | fqdn |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|capwap-ac-v4 |138 | ipv4-address | true | false |
|--------------------------------------+----+----------------------+------+-----------|
|sip-ua-cs-domains |142 | fqdn | true | false |
|--------------------------------------+----+----------------------+------+-----------|
| | | record (uint8, | | |
|rdnss-selection |146 | ipv4-address, | true | false |
| | | ipv4-address, fqdn) | | |
|--------------------------------------+----+----------------------+------+-----------|
|v4-portparams |159 | record (uint8, psid) |false | false |
|--------------------------------------+----+----------------------+------+-----------|
|v4-captive-portal |160 | string |false | false |
|--------------------------------------+----+----------------------+------+-----------|
| | |record (uint8, uint8, | | |
|option-6rd |212 | ipv6-address, | true | false |
| | | ipv4-address) | | |
|--------------------------------------+----+----------------------+------+-----------|
|v4-access-domain |213 | fqdn |false | false |
+-------------------------------------------------------------------------------------+
Table 8.2. List of standard DHCP option types
+------------------------------------------------------------------------+
| Name | Meaning |
|--------------+---------------------------------------------------------|
| hex | An arbitrary string of bytes, specified as a set of |
| | hexadecimal digits. |
|--------------+---------------------------------------------------------|
| boolean | Boolean value with allowed values true or false |
|--------------+---------------------------------------------------------|
| empty | No value, data is carried in suboptions |
|--------------+---------------------------------------------------------|
| fqdn | Fully qualified domain name (e.g. www.example.com) |
|--------------+---------------------------------------------------------|
| ipv4-address | IPv4 address in the usual dotted-decimal notation (e.g. |
| | 192.0.2.1) |
|--------------+---------------------------------------------------------|
| ipv6-address | IPv6 address in the usual colon notation (e.g. |
| | 2001:db8::1) |
|--------------+---------------------------------------------------------|
| | IPv6 prefix and prefix length specified using CIDR |
| ipv6-prefix | notation, e.g. 2001:db8:1::/64. This data type is used |
| | to represent an 8-bit field conveying a prefix length |
| | and the variable length prefix value |
|--------------+---------------------------------------------------------|
| | PSID and PSID length separated by a slash, e.g. 3/4 |
| | specifies PSID=3 and PSID length=4. In the wire format |
| | it is represented by an 8-bit field carrying PSID |
| psid | length (in this case equal to 4) and the 16-bits long |
| | PSID value field (in this case equal to |
| | "0011000000000000b" using binary notation). Allowed |
| | values for a PSID length are 0 to 16. See RFC 7597 for |
| | the details about the PSID wire representation |
|--------------+---------------------------------------------------------|
| | Structured data that may be comprised of any types |
| record | (except "record" and "empty"). The array flag applies |
| | to the last field only. |
|--------------+---------------------------------------------------------|
| string | Any text |
|--------------+---------------------------------------------------------|
| tuple | A length encoded as a 8 (16 for DHCPv6) bit unsigned |
| | integer followed by a string of this length |
|--------------+---------------------------------------------------------|
| uint8 | 8 bit unsigned integer with allowed values 0 to 255 |
|--------------+---------------------------------------------------------|
| uint16 | 16 bit unsigned integer with allowed values 0 to 65535 |
|--------------+---------------------------------------------------------|
| uint32 | 32 bit unsigned integer with allowed values 0 to |
| | 4294967295 |
|--------------+---------------------------------------------------------|
| int8 | 8 bit signed integer with allowed values -128 to 127 |
|--------------+---------------------------------------------------------|
| int16 | 16 bit signed integer with allowed values -32768 to |
| | 32767 |
|--------------+---------------------------------------------------------|
| int32 | 32 bit signed integer with allowed values -2147483648 |
| | to 2147483647 |
+------------------------------------------------------------------------+
8.2.9. Custom DHCPv4 options
Kea supports custom (non-standard) DHCPv4 options. Assume that we want to
define a new DHCPv4 option called "foo" which will have a code 222 and
will convey a single unsigned 32 bit integer value. We can define such an
option by using the following entry in the configuration file:
"Dhcp4": {
"option-def": [
{
"name": "foo",
"code": 222,
"type": "uint32",
"array": false,
"record-types": "",
"space": "dhcp4",
"encapsulate": ""
}, ...
],
...
}
The false value of the array parameter determines that the option does NOT
comprise an array of "uint32" values but is, instead, a single value. Two
other parameters have been left blank: record-types and encapsulate. The
former specifies the comma separated list of option data fields if the
option comprises a record of data fields. This should be non-empty if the
type is set to "record". Otherwise it must be left blank. The latter
parameter specifies the name of the option space being encapsulated by the
particular option. If the particular option does not encapsulate any
option space it should be left blank. Note that the above set of comments
define the format of the new option and do not set its values.
The name, code and type parameters are required, all others are optional.
The array default value is false. The record-types and encapsulate default
values are blank (i.e. ""). The default space is "dhcp4".
Once the new option format is defined, its value is set in the same way as
for a standard option. For example the following commands set a global
value that applies to all subnets.
"Dhcp4": {
"option-data": [
{
"name": "foo",
"code": 222,
"space": "dhcp4",
"csv-format": true,
"data": "12345"
}, ...
],
...
}
New options can take more complex forms than simple use of primitives
(uint8, string, ipv4-address etc): it is possible to define an option
comprising a number of existing primitives. Assume we want to define a new
option that will consist of an IPv4 address, followed by an unsigned 16
bit integer, followed by a boolean value, followed by a text string. Such
an option could be defined in the following way:
"Dhcp4": {
"option-def": [
{
"name": "bar",
"code": 223,
"space": "dhcp4",
"type": "record",
"array": false,
"record-types": "ipv4-address, uint16, boolean, string",
"encapsulate": ""
}, ...
],
...
}
The type is set to "record" to indicate that the option contains multiple
values of different types. These types are given as a comma-separated list
in the record-types field and should be ones from those listed in
Table 8.2, "List of standard DHCP option types".
The values of the option are set as follows:
"Dhcp4": {
"option-data": [
{
"name": "bar",
"space": "dhcp4",
"code": 223,
"csv-format": true,
"data": "192.0.2.100, 123, true, Hello World"
}
],
...
}
csv-format is set to true to indicate that the data field comprises a
command-separated list of values. The values in the data must correspond
to the types set in the record-types field of the option definition.
When array is set to true and type is set to "record", the last field is
an array, i.e., it can contain more than one value as in:
"Dhcp4": {
"option-def": [
{
"name": "bar",
"code": 223,
"space": "dhcp4",
"type": "record",
"array": true,
"record-types": "ipv4-address, uint16",
"encapsulate": ""
}, ...
],
...
}
The new option content is one IPv4 address followed by one or more 16 bit
unsigned integers.
Note
In the general case, boolean values are specified as true or false,
without quotes. Some specific boolean parameters may accept also "true",
"false", 0, 1, "0" and "1". Future versions of Kea will accept all those
values for all boolean parameters.
Note
Numbers can be specified in decimal or hexadecimal format. The hexadecimal
format can be either plain (e.g. abcd) or prefixed with 0x (e.g. 0xabcd).
8.2.10. DHCPv4 Private Options
Options with code between 224 and 254 are reserved for private use. They
can be defined at the global scope or at client class local scope: this
allows to use option definitions depending on context and to set option
data accordingly. For instance to configure an old PXEClient vendor:
"Dhcp4": {
"client-classes": [
{
"name": "pxeclient",
"test": "option[vendor-class-identifier].text == 'PXEClient'",
"option-def": [
{
"name": "configfile",
"code": 209,
"type": "string"
}
],
...
}, ...
],
...
}
As the Vendor Specific Information option (code 43) has vendor specific
format, i.e. can carry either raw binary value or sub-options, this
mechanism is available for this option too.
In the following example taken from a real configuration two vendor
classes use the option 43 for different and incompatible purposes:
"Dhcp4": {
"option-def": [
{
"name": "cookie",
"code": 1,
"type": "string",
"space": "APC"
},
{
"name": "mtftp-ip",
"code": 1,
"type": "ipv4-address",
"space": "PXE"
},
...
],
"client-classes": [
{
"name": "APC",
"test": "(option[vendor-class-identifier].text == 'APC'",
"option-def": [
{
"name": "vendor-encapsulated-options",
"type": "empty",
"encapsulate": "APC"
}
],
"option-data": [
{
"name": "cookie",
"space": "APC",
"data": "1APC"
},
{
"name": "vendor-encapsulated-options"
},
...
],
...
},
{
"name": "PXE",
"test": "(option[vendor-class-identifier].text == 'PXE'",
"option-def": [
{
"name": "vendor-encapsulated-options",
"type": "empty",
"encapsulate": "PXE"
}
],
"option-data": [
{
"name": "mtftp-ip",
"space": "PXE",
"data": "0.0.0.0"
},
{
"name": "vendor-encapsulated-options"
},
...
],
...
},
...
],
...
}
The definition used to decode a VSI option is:
1. The local definition of a client class the incoming packet belongs to
2. If none, the global definition
3. If none, the last resort definition described in the next section
Section 8.2.11, "DHCPv4 Vendor Specific Options" (backward compatible
with previous Kea versions).
Note
This last resort definition for the Vendor Specific Information option
(code 43) is not compatible with a raw binary value. So when there are
some known cases where a raw binary value will be used, a client class
must be defined with a classification expression matching these cases and
an option definition for the VSI option with a binary type and no
encapsulation.
Note
Option definitions in client classes is allowed only for these limited
option set (codes 43 and from 224 to 254), and only for DHCPv4.
8.2.11. DHCPv4 Vendor Specific Options
Currently there are two option spaces defined for the DHCPv4 daemon:
"dhcp4" (for the top level DHCPv4 options) and
"vendor-encapsulated-options-space", which is empty by default but in
which options can be defined. Such options will be carried in the Vendor
Specific Information option (code 43). The following examples show how to
define an option "foo" in that space that has a code 1, and comprises an
IPv4 address, an unsigned 16 bit integer and a string. The "foo" option is
conveyed in a Vendor Specific Information option.
The first step is to define the format of the option:
"Dhcp4": {
"option-def": [
{
"name": "foo",
"code": 1,
"space": "vendor-encapsulated-options-space",
"type": "record",
"array": false,
"record-types": "ipv4-address, uint16, string",
"encapsulate": ""
}
],
...
}
(Note that the option space is set to
"vendor-encapsulated-options-space".) Once the option format is defined,
the next step is to define actual values for that option:
"Dhcp4": {
"option-data": [
{
"name": "foo",
"space": "vendor-encapsulated-options-space",
"code": 1,
"csv-format": true,
"data": "192.0.2.3, 123, Hello World"
}
],
...
}
We also include the Vendor Specific Information option, the option that
conveys our sub-option "foo". This is required, else the option will not
be included in messages sent to the client.
"Dhcp4": {
"option-data": [
{
"name": "vendor-encapsulated-options"
}
],
...
}
Alternatively, the option can be specified using its code.
"Dhcp4": {
"option-data": [
{
"code": 43
}
],
...
}
Another possibility, since Kea 1.3, is to redefine the option, see
Section 8.2.10, "DHCPv4 Private Options".
8.2.12. Nested DHCPv4 Options (Custom Option Spaces)
It is sometimes useful to define a completely new option space. This is
the case when user creates new option in the standard option space
("dhcp4") and wants this option to convey sub-options. Since they are in a
separate space, sub-option codes will have a separate numbering scheme and
may overlap with the codes of standard options.
Note that creation of a new option space when defining sub-options for a
standard option is not required, because it is created by default if the
standard option is meant to convey any sub-options (see Section 8.2.11,
"DHCPv4 Vendor Specific Options").
Assume that we want to have a DHCPv4 option called "container" with code
222 that conveys two sub-options with codes 1 and 2. First we need to
define the new sub-options:
"Dhcp4": {
"option-def": [
{
"name": "subopt1",
"code": 1,
"space": "isc",
"type": "ipv4-address",
"record-types": "",
"array": false,
"encapsulate": ""
},
{
"name": "subopt2",
"code": 2,
"space": "isc",
"type": "string",
"record-types": "",
"array": false,
"encapsulate": ""
}
],
...
}
Note that we have defined the options to belong to a new option space (in
this case, "isc").
The next step is to define a regular DHCPv4 option with our desired code
and specify that it should include options from the new option space:
"Dhcp4": {
"option-def": [
...,
{
"name": "container",
"code": 222,
"space": "dhcp4",
"type": "empty",
"array": false,
"record-types": "",
"encapsulate": "isc"
}
],
...
}
The name of the option space in which the sub-options are defined is set
in the encapsulate field. The type field is set to "empty" to indicate
that this option does not carry any data other than sub-options.
Finally, we can set values for the new options:
"Dhcp4": {
"option-data": [
{
"name": "subopt1",
"code": 1,
"space": "isc",
"data": "192.0.2.3"
},
}
"name": "subopt2",
"code": 2,
"space": "isc",
"data": "Hello world"
},
{
"name": "container",
"code": 222,
"space": "dhcp4"
}
],
...
}
Note that it is possible to create an option which carries some data in
addition to the sub-options defined in the encapsulated option space. For
example, if the "container" option from the previous example was required
to carry an uint16 value as well as the sub-options, the type value would
have to be set to "uint16" in the option definition. (Such an option would
then have the following data structure: DHCP header, uint16 value,
sub-options.) The value specified with the data parameter -- which should
be a valid integer enclosed in quotes, e.g. "123" -- would then be
assigned to the uint16 field in the "container" option.
8.2.13. Unspecified Parameters for DHCPv4 Option Configuration
In many cases it is not required to specify all parameters for an option
configuration and the default values may be used. However, it is important
to understand the implications of not specifying some of them as it may
result in configuration errors. The list below explains the behavior of
the server when a particular parameter is not explicitly specified:
* name - the server requires an option name or option code to identify
an option. If this parameter is unspecified, the option code must be
specified.
* code - the server requires an option name or option code to identify
an option. This parameter may be left unspecified if the name
parameter is specified. However, this also requires that the
particular option has its definition (it is either a standard option
or an administrator created a definition for the option using an
'option-def' structure), as the option definition associates an option
with a particular name. It is possible to configure an option for
which there is no definition (unspecified option format).
Configuration of such options requires the use of option code.
* space - if the option space is unspecified it will default to 'dhcp4'
which is an option space holding DHCPv4 standard options.
* data - if the option data is unspecified it defaults to an empty
value. The empty value is mostly used for the options which have no
payload (boolean options), but it is legal to specify empty values for
some options which carry variable length data and which the
specification allows for the length of 0. For such options, the data
parameter may be omitted in the configuration.
* csv-format - if this value is not specified the server will assume
that the option data is specified as a list of comma separated values
to be assigned to individual fields of the DHCP option. This behavior
has changed in Kea 1.2. Older versions used additional logic to
determine whether the csv-format should be true or false. That is no
longer the case.
8.2.14. Stateless Configuration of DHCPv4 Clients
The DHCPv4 server supports the stateless client configuration whereby the
client has an IP address configured (e.g. using manual configuration) and
only contacts the server to obtain other configuration parameters, e.g.
addresses of DNS servers. In order to obtain the stateless configuration
parameters the client sends the DHCPINFORM message to the server with the
"ciaddr" set to the address that the client is currently using. The server
unicasts the DHCPACK message to the client that includes the stateless
configuration ("yiaddr" not set).
The server will respond to the DHCPINFORM when the client is associated
with a subnet defined in the server's configuration. An example subnet
configuration will look like this:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24"
"option-data": [ {
"name": "domain-name-servers",
"code": 6,
"data": "192.0.2.200,192.0.2.201",
"csv-format": true,
"space": "dhcp4"
} ]
}
]
}
This subnet specifies the single option which will be included in the
DHCPACK message to the client in response to DHCPINFORM. Note that the
subnet definition does not require the address pool configuration if it
will be used solely for the stateless configuration.
This server will associate the subnet with the client if one of the
following conditions is met:
* The DHCPINFORM is relayed and the giaddr matches the configured
subnet.
* The DHCPINFORM is unicast from the client and the ciaddr matches the
configured subnet.
* The DHCPINFORM is unicast from the client, the ciaddr is not set but
the source address of the IP packet matches the configured subnet.
* The DHCPINFORM is not relayed and the IP address on the interface on
which the message is received matches the configured subnet.
8.2.15. Client Classification in DHCPv4
The DHCPv4 server includes support for client classification. For a deeper
discussion of the classification process see Chapter 13, Client
Classification.
In certain cases it is useful to differentiate between different types of
clients and treat them accordingly. It is envisaged that client
classification will be used for changing the behavior of almost any part
of the DHCP message processing. In the current release of the software
however, there are only some mechanisms that take advantage of client
classification: private options and option 43 deferred unpacking, subnet
selection, pool selection, assignment of different options, and, for cable
modems, there are specific options for use with the TFTP server address
and the boot file field.
Kea can be instructed to limit access to given subnets based on class
information. This is particularly useful for cases where two types of
devices share the same link and are expected to be served from two
different subnets. The primary use case for such a scenario is cable
networks. Here, there are two classes of devices: the cable modem itself,
which should be handed a lease from subnet A and all other devices behind
the modem that should get a lease from subnet B. That segregation is
essential to prevent overly curious users from playing with their cable
modems. For details on how to set up class restrictions on subnets, see
Section 13.6, "Configuring Subnets With Class Information".
When subnets belong to a shared network the classification applies to
subnet selection but not to pools, e.g., a pool in a subnet limited to a
particular class can still be used by clients which do not belong to the
class if the pool they are expected to use is exhausted. So the limit
access based on class information is also available at the pool level, see
Section 13.7, "Configuring Pools With Class Information", within a subnet.
This is useful when to segregate clients belonging to the same subnet into
different address ranges.
In a similar way a pool can be constrained to serve only known clients,
i.e. clients which have a reservation, using the built-in "KNOWN" or
"UNKNOWN" classes. One can assign addresses to registered clients without
giving a different address per reservations, for instance when there is
not enough available addresses. The determination whether there is a
reservation for a given client is made after a subnet is selected. As
such, it is not possible to use KNOWN/UNKNOWN classes to select a shared
network or a subnet.
The process of doing classification is conducted in five steps. The first
step is to assess an incoming packet and assign it to zero or more
classes. The second step is to choose a subnet, possibly based on the
class information. The next step is to evaluate class expressions
depending on the built-in "KNOWN"/"UNKNOWN" classes after host reservation
lookup, using them for pool selection and to assign classes from host
reservations. After the list of required classes is built and each class
of the list has its expression evaluated: when it returns true the packet
is added as a member of the class. The last step is to assign options,
again possibly based on the class information. More complete and detailed
description is available in Chapter 13, Client Classification.
There are two main methods of doing classification. The first is automatic
and relies on examining the values in the vendor class options or
existence of a host reservation. Information from these options is
extracted and a class name is constructed from it and added to the class
list for the packet. The second allows for specifying an expression that
is evaluated for each packet. If the result is true the packet is a member
of the class.
Note
Care should be taken with client classification as it is easy for clients
that do not meet class criteria to be denied any service altogether.
8.2.15.1. Setting Fixed Fields in Classification
It is possible to specify that clients belonging to a particular class
should receive packets with specific values in certain fixed fields. In
particular, three fixed fields are supported: next-server (that conveys an
IPv4 address, which is set in the siaddr field), server-hostname (that
conveys a server hostname, can be up to 64 bytes long and will be sent in
the sname field) and boot-file-name (that conveys the configuration file,
can be up to 128 bytes long and will be sent using file field).
Obviously, there are many ways to assign clients to specific classes, but
for the PXE clients the client architecture type option (code 93) seems to
be particularly suited to make the distinction. The following example
checks if the client identifies itself as PXE device with architecture EFI
x86-64, and sets several fields if it does. See Section 2.1 of RFC 4578)
or the documentation of your client for specific values.
"Dhcp4": {
"client-classes": [
{
"name": "ipxe_efi_x64",
"test": "option[93].hex == 0x0009",
"next-server": "192.0.2.254",
"server-hostname": "hal9000",
"boot-file-name": "/dev/null"
},
...
],
...
}
If there are multiple classes defined and an incoming packet is matched to
multiple classes, the class which is evaluated first is used.
Note
In Kea versions prior to 1.4.0 the alphabetical order of class names was
used. Starting from Kea 1.4.0 the classes are ordered as specified in the
configuration.
8.2.15.2. Using Vendor Class Information in Classification
The server checks whether an incoming packet includes the vendor class
identifier option (60). If it does, the content of that option is
prepended with "VENDOR_CLASS_", it is interpreted as a class. For example,
modern cable modems will send this option with value "docsis3.0" and as a
result the packet will belong to class "VENDOR_CLASS_docsis3.0".
Note
Kea 1.0 and earlier versions performed special actions for clients that
were in VENDOR_CLASS_docsis3.0. This is no longer the case in Kea 1.1 and
later. In these versions the old behavior can be achieved by defining
VENDOR_CLASS_docsis3.0 and setting its next-server and boot-file-name
values appropriately.
This example shows a configuration using an automatically generated
"VENDOR_CLASS_" class. The administrator of the network has decided that
addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed by
the Dhcp4 server and only clients belonging to the docsis3.0 client class
are allowed to use that pool.
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"client-class": "VENDOR_CLASS_docsis3.0"
}
],
...
}
8.2.15.3. Defining and Using Custom Classes
The following example shows how to configure a class using an expression
and a subnet that makes use of the class. This configuration defines the
class named "Client_foo". It is comprised of all clients who's client ids
(option 61) start with the string "foo". Members of this class will be
given addresses from 192.0.2.10 to 192.0.2.20 and the addresses of their
DNS servers set to 192.0.2.1 and 192.0.2.2.
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"client-class": "Client_foo"
},
...
],
...
}
8.2.15.4. Required Classification
In some cases it is useful to limit the scope of a class to a
shared-network, subnet or pool. There are two parameters which are used to
limit the scope of the class by instructing the server to perform
evaluation of test expressions when required.
The first one is the per-class only-if-required flag which is false by
default. When it is set to true the test expression of the class is not
evaluated at the reception of the incoming packet but later and only if
the class evaluation is required.
The second is the require-client-classes which takes a list of class names
and is valid in shared-network, subnet and pool scope. Classes in these
lists are marked as required and evaluated after selection of this
specific shared-network/subnet/pool and before output option processing.
In this example, a class is assigned to the incoming packet when the
specified subnet is used.
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "member('ALL')",
"only-if-required": true
},
...
],
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"require-client-classes": [ "Client_foo" ],
...
},
...
],
...
}
Required evaluation can be used to express complex dependencies, for
example, subnet membership. It can also be used to reverse the precedence:
if you set an option-data in a subnet it takes precedence over an
option-data in a class. When you move the option-data to a required class
and require it in the subnet, a class evaluated earlier may take
precedence.
Required evaluation is also available at shared-network and pool levels.
The order in which required classes are considered is: shared-network,
subnet and pool, i.e. the opposite order option-data are processed.
8.2.16. DDNS for DHCPv4
As mentioned earlier, kea-dhcp4 can be configured to generate requests to
the DHCP-DDNS server (referred to here as "D2" ) to update DNS entries.
These requests are known as NameChangeRequests or NCRs. Each NCR contains
the following information:
1. Whether it is a request to add (update) or remove DNS entries
2. Whether the change requests forward DNS updates (A records), reverse
DNS updates (PTR records), or both.
3. The FQDN, lease address, and DHCID
The parameters for controlling the generation of NCRs for submission to D2
are contained in the dhcp-ddns section of the kea-dhcp4 server
configuration. The mandatory parameters for the DHCP DDNS configuration
are enable-updates which is unconditionally required, and
qualifying-suffix which has no default value and is required when
enable-updates is set to true. The two (disabled and enabled) minimal DHCP
DDNS configurations are:
"Dhcp4": {
"dhcp-ddns": {
"enable-updates": false
},
...
}
and for example:
"Dhcp4": {
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example."
},
...
}
The default values for the "dhcp-ddns" section are as follows:
* "server-ip": "127.0.0.1"
* "server-port": 53001
* "sender-ip": ""
* "sender-port": 0
* "max-queue-size": 1024
* "ncr-protocol": "UDP"
* "ncr-format": "JSON"
* "override-no-update": false
* "override-client-update": false
* "replace-client-name": "never"
* "generated-prefix": "myhost"
8.2.16.1. DHCP-DDNS Server Connectivity
In order for NCRs to reach the D2 server, kea-dhcp4 must be able to
communicate with it. kea-dhcp4 uses the following configuration parameters
to control this communication:
* enable-updates - determines whether or not kea-dhcp4 will generate
NCRs. By default, this value is false hence DDNS updates are disabled.
To enable DDNS updates set this value to true:
* server-ip - IP address on which D2 listens for requests. The default
is the local loopback interface at address 127.0.0.1. You may specify
either an IPv4 or IPv6 address.
* server-port - port on which D2 listens for requests. The default value
is 53001.
* sender-ip - IP address which kea-dhcp4 should use to send requests to
D2. The default value is blank which instructs kea-dhcp4 to select a
suitable address.
* sender-port - port which kea-dhcp4 should use to send requests to D2.
The default value of 0 instructs kea-dhcp4 to select a suitable port.
* max-queue-size - maximum number of requests allowed to queue waiting
to be sent to D2. This value guards against requests accumulating
uncontrollably if they are being generated faster than they can be
delivered. If the number of requests queued for transmission reaches
this value, DDNS updating will be turned off until the queue backlog
has been sufficiently reduced. The intention is to allow the kea-dhcp4
server to continue lease operations without running the risk that its
memory usage grows without limit. The default value is 1024.
* ncr-protocol - socket protocol use when sending requests to D2.
Currently only UDP is supported. TCP may be available in an upcoming
release.
* ncr-format - packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be
available in future releases.
By default, kea-dhcp-ddns is assumed to be running on the same machine as
kea-dhcp4, and all of the default values mentioned above should be
sufficient. If, however, D2 has been configured to listen on a different
address or port, these values must be altered accordingly. For example, if
D2 has been configured to listen on 192.168.1.10 port 900, the following
configuration would be required:
"Dhcp4": {
"dhcp-ddns": {
"server-ip": "192.168.1.10",
"server-port": 900,
...
},
...
}
8.2.16.2. When Does the kea-dhcp4 Server Generate DDNS Requests?
kea-dhcp4 follows the behavior prescribed for DHCP servers in RFC 4702. It
is important to keep in mind that kea-dhcp4 provides the initial decision
making of when and what to update and forwards that information to D2 in
the form of NCRs. Carrying out the actual DNS updates and dealing with
such things as conflict resolution are within the purview of D2 itself
(Chapter 11, The DHCP-DDNS Server). This section describes when kea-dhcp4
will generate NCRs and the configuration parameters that can be used to
influence this decision. It assumes that the enable-updates parameter is
true.
In general, kea-dhcp4 will generate DDNS update requests when:
1. A new lease is granted in response to a DHCP REQUEST
2. An existing lease is renewed but the FQDN associated with it has
changed.
3. An existing lease is released in response to a DHCP RELEASE
In the second case, lease renewal, two DDNS requests will be issued: one
request to remove entries for the previous FQDN and a second request to
add entries for the new FQDN. In the last case, a lease release, a single
DDNS request to remove its entries will be made.
The decision making involved when granting a new lease (the first case) is
more involved. When a new lease is granted, kea-dhcp4 will generate a DDNS
update request if the DHCP REQUEST contains either the FQDN option (code
81) or the Host Name option (code 12). If both are present, the server
will use the FQDN option. By default kea-dhcp4 will respect the FQDN N and
S flags specified by the client as shown in the following table:
Table 8.3. Default FQDN Flag Behavior
+------------------------------------------------------------------------+
| Client | Client Intent | Server Response | Server |
| Flags:N-S | | | Flags:N-S-O |
|-----------+-------------------------+--------------------+-------------|
| | Client wants to do | Server generates | |
| 0-0 | forward updates, server | reverse-only | 1-0-0 |
| | should do reverse | request | |
| | updates | | |
|-----------+-------------------------+--------------------+-------------|
| | Server should do both | Server generates | |
| 0-1 | forward and reverse | request to update | 0-1-0 |
| | updates | both directions | |
|-----------+-------------------------+--------------------+-------------|
| 1-0 | Client wants no updates | Server does not | 1-0-0 |
| | done | generate a request | |
+------------------------------------------------------------------------+
The first row in the table above represents "client delegation". Here the
DHCP client states that it intends to do the forward DNS updates and the
server should do the reverse updates. By default, kea-dhcp4 will honor the
client's wishes and generate a DDNS request to the D2 server to update
only reverse DNS data. The parameter override-client-update can be used to
instruct the server to override client delegation requests. When this
parameter is true, kea-dhcp4 will disregard requests for client delegation
and generate a DDNS request to update both forward and reverse DNS data.
In this case, the N-S-O flags in the server's response to the client will
be 0-1-1 respectively.
(Note that the flag combination N=1, S=1 is prohibited according to RFC
4702. If such a combination is received from the client, the packet will
be dropped by kea-dhcp4.)
To override client delegation, set the following values in the
configuration file:
"Dhcp4": {
"dhcp-ddns": {
"override-client-update": true,
...
},
...
}
The third row in the table above describes the case in which the client
requests that no DNS updates be done. The parameter, override-no-update,
can be used to instruct the server to disregard the client's wishes. When
this parameter is true, kea-dhcp4 will generate DDNS update requests to
kea-dhcp-ddns even if the client requests that no updates be done. The
N-S-O flags in the server's response to the client will be 0-1-1.
To override client delegation, the following values should be set in your
configuration:
"Dhcp4": {
"dhcp-ddns": {
"override-no-update": true,
...
},
...
}
kea-dhcp4 will always generate DDNS update requests if the client request
only contains the Host Name option. In addition it will include an FQDN
option in the response to the client with the FQDN N-S-O flags set to
0-1-0 respectively. The domain name portion of the FQDN option will be the
name submitted to D2 in the DDNS update request.
8.2.16.3. kea-dhcp4 name generation for DDNS update requests
Each NameChangeRequest must of course include the fully qualified domain
name whose DNS entries are to be affected. kea-dhcp4 can be configured to
supply a portion or all of that name based upon what it receives from the
client in the DHCP REQUEST.
The default rules for constructing the FQDN that will be used for DNS
entries are:
1. If the DHCPREQUEST contains the client FQDN option, the candidate name
is taken from there, otherwise it is taken from the Host Name option.
2. If the candidate name is a partial (i.e. unqualified) name then add a
configurable suffix to the name and use the result as the FQDN.
3. If the candidate name provided is empty, generate a FQDN using a
configurable prefix and suffix.
4. If the client provided neither option, then no DNS action will be
taken.
These rules can amended by setting the replace-client-name parameter which
provides the following modes of behavior:
* never - Use the name the client sent. If the client sent no name, do
not generate one. This is the default mode.
* always - Replace the name the client sent. If the client sent no name,
generate one for the client.
* when-present - Replace the name the client sent. If the client sent no
name, do not generate one.
* when-not-present - Use the name the client sent. If the client sent no
name, generate one for the client.
Note
Note that formerly, this parameter was a boolean and permitted only values
of true and false. Boolean values have been deprecated and are no longer
accepted. If you are currently using booleans, you must replace them with
the desired mode name. A value of true maps to "when-present", while false
maps to "never".
For example, To instruct kea-dhcp4 to always generate the FQDN for a
client, set the parameter replace-client-name to always as follows:
"Dhcp4": {
"dhcp-ddns": {
"replace-client-name": "always",
...
},
...
}
The prefix used in the generation of a FQDN is specified by the
generated-prefix parameter. The default value is "myhost". To alter its
value, simply set it to the desired string:
"Dhcp4": {
"dhcp-ddns": {
"generated-prefix": "another.host",
...
},
...
}
The suffix used when generating a FQDN or when qualifying a partial name
is specified by the qualifying-suffix parameter. This parameter has no
default value, thus it is mandatory when DDNS updates are enabled. To set
its value simply set it to the desired string:
"Dhcp4": {
"dhcp-ddns": {
"qualifying-suffix": "foo.example.org",
...
},
...
}
When generating a name, kea-dhcp4 will construct name of the format:
[generated-prefix]-[address-text].[qualifying-suffix].
where address-text is simply the lease IP address converted to a
hyphenated string. For example, if the lease address is 172.16.1.10, the
qualifying suffix "example.com", and the default value is used for
generated-prefix, the generated FQDN would be:
myhost-172-16-1-10.example.com.
8.2.17. Next Server (siaddr)
In some cases, clients want to obtain configuration from a TFTP server.
Although there is a dedicated option for it, some devices may use the
siaddr field in the DHCPv4 packet for that purpose. That specific field
can be configured using next-server directive. It is possible to define it
in the global scope or for a given subnet only. If both are defined, the
subnet value takes precedence. The value in subnet can be set to 0.0.0.0,
which means that next-server should not be sent. It may also be set to an
empty string, which means the same as if it was not defined at all, i.e.
use the global value.
The server-hostname (that conveys a server hostname, can be up to 64 bytes
long and will be sent in the sname field) and boot-file-name (that conveys
the configuration file, can be up to 128 bytes long and will be sent using
file field) directives are handled the same way as next-server.
"Dhcp4": {
"next-server": "192.0.2.123",
"boot-file-name": "/dev/null",
...,
"subnet4": [
{
"next-server": "192.0.2.234",
"server-hostname": "some-name.example.org",
"boot-file-name": "bootfile.efi",
...
}
]
}
8.2.18. Echoing Client-ID (RFC 6842)
The original DHCPv4 specification (RFC 2131) states that the DHCPv4 server
must not send back client-id options when responding to clients. However,
in some cases that confused clients that did not have MAC address or
client-id; see RFC 6842. for details. That behavior has changed with the
publication of RFC 6842 which updated RFC 2131. That update states that
the server must send client-id if the client sent it. That is Kea's
default behavior. However, in some cases older devices that do not support
RFC 6842. may refuse to accept responses that include the client-id
option. To enable backward compatibility, an optional configuration
parameter has been introduced. To configure it, use the following
configuration statement:
"Dhcp4": {
"echo-client-id": false,
...
}
8.2.19. Using Client Identifier and Hardware Address
The DHCP server must be able to identify the client (and distinguish it
from other clients) from which it receives the message. There are many
reasons why this identification is required and the most important ones
are:
* When the client contacts the server to allocate a new lease, the
server must store the client identification information in the lease
database as a search key.
* When the client is trying to renew or release the existing lease, the
server must be able to find the existing lease entry in the database
for this client, using the client identification information as a
search key.
* Some configurations use static reservations for the IP addresses and
other configuration information. The server's administrator uses
client identification information to create these static assignments.
* In the dual stack networks there is often a need to correlate the
lease information stored in DHCPv4 and DHCPv6 server for a particular
host. Using common identification information by the DHCPv4 and DHCPv6
client allows the network administrator to achieve this correlation
and better administer the network.
DHCPv4 makes use of two distinct identifiers which are placed by the
client in the queries sent to the server and copied by the server to its
responses to the client: "chaddr" and "client identifier". The former was
introduced as a part of the BOOTP specification and it is also used by
DHCP to carry the hardware address of the interface used to send the query
to the server (MAC address for the Ethernet). The latter is carried in the
Client-identifier option, introduced in RFC 2132.
RFC 2131 indicates that the server may use both of these identifiers to
identify the client but the "client identifier", if present, takes
precedence over "chaddr". One of the reasons for this is that "client
identifier" is independent from the hardware used by the client to
communicate with the server. For example, if the client obtained the lease
using one network card and then the network card is moved to another host,
the server will wrongly identify this host is the one which has obtained
the lease. Moreover, RFC 4361 gives the recommendation to use a DUID (see
RFC 3315, the DHCPv6 specification) carried as "client identifier" when
dual stack networks are in use to provide consistent identification
information of the client, regardless of the protocol type it is using.
Kea adheres to these specifications and the "client identifier" by default
takes precedence over the value carried in "chaddr" field when the server
searches, creates, updates or removes the client's lease.
When the server receives a DHCPDISCOVER or DHCPREQUEST message from the
client, it will try to find out if the client already has a lease in the
database and will hand out that lease rather than allocate a new one. Each
lease in the lease database is associated with the "client identifier"
and/or "chaddr". The server will first use the "client identifier" (if
present) to search the lease. If the lease is found, the server will treat
this lease as belonging to the client even if the current "chaddr" and the
"chaddr" associated with the lease do not match. This facilitates the
scenario when the network card on the client system has been replaced and
thus the new MAC address appears in the messages sent by the DHCP client.
If the server fails to find the lease using the "client identifier" it
will perform another lookup using the "chaddr". If this lookup returns no
result, the client is considered as not having a lease and the new lease
will be created.
A common problem reported by network operators is that poor client
implementations do not use stable client identifiers, instead generating a
new "client identifier" each time the client connects to the network.
Another well known case is when the client changes its "client identifier"
during the multi-stage boot process (PXE). In such cases, the MAC address
of the client's interface remains stable and using "chaddr" field to
identify the client guarantees that the particular system is considered to
be the same client, even though its "client identifier" changes.
To address this problem, Kea includes a configuration option which enables
client identification using "chaddr" only by instructing the server to
disregard server to "ignore" the "client identifier" during lease lookups
and allocations for a particular subnet. Consider the following simplified
server configuration:
"Dhcp4": {
...
"match-client-id": true,
...
"subnet4": [
{
"subnet": "192.0.10.0/24",
"pools": [ { "pool": "192.0.2.23-192.0.2.87" } ],
"match-client-id": false
},
{
"subnet": "10.0.0.0/8",
"pools": [ { "pool": "10.0.0.23-10.0.2.99" } ],
}
]
}
The match-client-id is a boolean value which controls this behavior. The
default value of true indicates that the server will use the "client
identifier" for lease lookups and "chaddr" if the first lookup returns no
results. The false means that the server will only use the "chaddr" to
search for client's lease. Whether the DHCID for DNS updates is generated
from the "client identifier" or "chaddr" is controlled through the same
parameter accordingly.
The match-client-id parameter may appear both in the global configuration
scope and/or under any subnet declaration. In the example shown above, the
effective value of the match-client-id will be false for the subnet
192.0.10.0/24, because the subnet specific setting of the parameter
overrides the global value of the parameter. The effective value of the
match-client-id for the subnet 10.0.0.0/8 will be set to true because the
subnet declaration lacks this parameter and the global setting is by
default used for this subnet. In fact, the global entry for this parameter
could be omitted in this case, because true is the default value.
It is important to explain what happens when the client obtains its lease
for one setting of the match-client-id and then renews when the setting
has been changed. First consider the case when the client obtains the
lease when the match-client-id is set to true. The server will store the
lease information including "client identifier" (if supplied) and "chaddr"
in the lease database. When the setting is changed and the client renews
the lease the server will determine that it should use the "chaddr" to
search for the existing lease. If the client hasn't changed its MAC
address the server should successfully find the existing lease. The
"client identifier" associated with the returned lease is ignored and the
client is allowed to use this lease. When the lease is renewed only the
"chaddr" is recorded for this lease according to the new server setting.
In the second case the client has the lease with only a "chaddr" value
recorded. When the setting is changed to match-client-id set to true the
server will first try to use the "client identifier" to find the existing
client's lease. This will return no results because the "client
identifier" was not recorded for this lease. The server will then use the
"chaddr" and the lease will be found. If the lease appears to have no
"client identifier" recorded, the server will assume that this lease
belongs to the client and that it was created with the previous setting of
the match-client-id. However, if the lease contains "client identifier"
which is different from the "client identifier" used by the client the
lease will be assumed to belong to another client and the new lease will
be allocated.
8.2.20. DHCPv4-over-DHCPv6: DHCPv4 Side
The support of DHCPv4-over-DHCPv6 transport is described in RFC 7341 and
is implemented using cooperating DHCPv4 and DHCPv6 servers. This section
is about the configuration of the DHCPv4 side (the DHCPv6 side is
described in Section 9.2.22, "DHCPv4-over-DHCPv6: DHCPv6 Side").
Note
DHCPv4-over-DHCPv6 support is experimental and the details of the
inter-process communication can change: both the DHCPv4 and DHCPv6 sides
should be running the same version of Kea. For instance the support of
port relay (RFC 8357) introduced such incompatible change.
The dhcp4o6-port global parameter specifies the first of the two
consecutive ports of the UDP sockets used for the communication between
the DHCPv6 and DHCPv4 servers (the DHCPv4 server is bound to ::1 on port +
1 and connected to ::1 on port).
With DHCPv4-over-DHCPv6 the DHCPv4 server does not have access to several
of the identifiers it would normally use to select a subnet. In order to
address this issue three new configuration entries have been added. The
presence of any of these allows the subnet to be used with
DHCPv4-over-DHCPv6. These entries are:
* 4o6-subnet: Takes a prefix (i.e., an IPv6 address followed by a slash
and a prefix length) which is matched against the source address.
* 4o6-interface-id: Takes a relay interface ID option value.
* 4o6-interface: Takes an interface name which is matched against the
incoming interface name.
The following configuration was used during some tests:
{
# DHCPv4 conf
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eno33554984" ]
},
"lease-database": {
"type": "memfile",
"name": "leases4"
},
"valid-lifetime": 4000,
"subnet4": [ {
"subnet": "10.10.10.0/24",
"4o6-interface": "eno33554984",
"4o6-subnet": "2001:db8:1:1::/64",
"pools": [ { "pool": "10.10.10.100 - 10.10.10.199" } ]
} ],
"dhcp4o6-port": 6767
},
"Logging": {
"loggers": [ {
"name": "kea-dhcp4",
"output_options": [ {
"output": "/tmp/kea-dhcp4.log"
} ],
"severity": "DEBUG",
"debuglevel": 0
} ]
}
}
8.3. Host Reservation in DHCPv4
There are many cases where it is useful to provide a configuration on a
per host basis. The most obvious one is to reserve a specific, static
address for exclusive use by a given client (host) - the returning client
will receive the same address from the server every time, and other
clients will generally not receive that address. Another example when the
host reservations are applicable is when a host has specific requirements,
e.g. a printer that needs additional DHCP options. Yet another possible
use case is to define unique names for hosts.
Note that there may be cases when the new reservation has been made for
the client for the address being currently in use by another client. We
call this situation a "conflict". The conflicts get resolved automatically
over time as described in subsequent sections. Once the conflict is
resolved, the client will keep receiving the reserved configuration when
it renews.
Host reservations are defined as parameters for each subnet. Each host has
to be identified by an identifier, for example the hardware/MAC address.
There is an optional reservations array in the Subnet4 element. Each
element in that array is a structure that holds information about
reservations for a single host. In particular, the structure has to have
an identifier that uniquely identifies a host. In the DHCPv4 context, the
identifier is usually a hardware or MAC address. In most cases an IP
address will be specified. It is also possible to specify a hostname, host
specific options or fields carried within DHCPv4 message such as siaddr,
sname or file.
In Kea 1.0.0 it was only possible to create host reservations using
client's hardware address. Host reservations by client identifier, DUID
and circuit-id have been added in Kea 1.1.0.
The following example shows how to reserve addresses for specific hosts:
"subnet4": [
{
"pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
"subnet": "192.0.2.0/24",
"interface": "eth0",
"reservations": [
{
"hw-address": "1a:1b:1c:1d:1e:1f",
"ip-address": "192.0.2.202"
},
{
"duid": "0a:0b:0c:0d:0e:0f",
"ip-address": "192.0.2.100",
"hostname": "alice-laptop"
},
{
"circuit-id": "'charter950'",
"ip-address": "192.0.2.203"
},
{
"client-id": "01:11:22:33:44:55:66",
"ip-address": "192.0.2.204"
}
]
}
]
The first entry reserves the 192.0.2.202 address for the client that uses
a MAC address of 1a:1b:1c:1d:1e:1f. The second entry reserves the address
192.0.2.100 and the hostname of alice-laptop for the client using a DUID
0a:0b:0c:0d:0e:0f. (Note that if you plan to do DNS updates, it is
strongly recommended for the hostnames to be unique.) The third example
reserves address 192.0.3.203 to a client whose request would be relayed by
a relay agent that inserts a circuit-it option with the value
'charter950'. The fourth entry reserves address 192.0.2.204 for a client
that uses a client identifier with value 01:11:22:33:44:55:66.
The above example is used for illustrational purposes only and in actual
deployments it is recommended to use as few types as possible (preferably
just one). See Section 8.3.8, "Fine Tuning DHCPv4 Host Reservation" for a
detailed discussion of this point.
Making a reservation for a mobile host that may visit multiple subnets
requires a separate host definition in each subnet it is expected to
visit. It is not allowed to define multiple host definitions with the same
hardware address in a single subnet. Multiple host definitions with the
same hardware address are valid if each is in a different subnet.
Adding host reservation incurs a performance penalty. In principle, when a
server that does not support host reservation responds to a query, it
needs to check whether there is a lease for a given address being
considered for allocation or renewal. The server that also supports host
reservation has to perform additional checks: not only if the address is
currently used (i.e. if there is a lease for it), but also whether the
address could be used by someone else (i.e. there is a reservation for
it). That additional check incurs additional overhead.
8.3.1. Address Reservation Types
In a typical scenario there is an IPv4 subnet defined, e.g. 192.0.2.0/24,
with certain part of it dedicated for dynamic allocation by the DHCPv4
server. That dynamic part is referred to as a dynamic pool or simply a
pool. In principle, a host reservation can reserve any address that
belongs to the subnet. The reservations that specify addresses that belong
to configured pools are called "in-pool reservations". In contrast, those
that do not belong to dynamic pools are called "out-of-pool reservations".
There is no formal difference in the reservation syntax and both
reservation types are handled uniformly. However, upcoming releases may
offer improved performance if there are only out-of-pool reservations as
the server will be able to skip reservation checks when dealing with
existing leases. Therefore, system administrators are encouraged to use
out-of-pool reservations if possible.
8.3.2. Conflicts in DHCPv4 Reservations
As the reservations and lease information are stored separately, conflicts
may arise. Consider the following series of events. The server has
configured the dynamic pool of addresses from the range of 192.0.2.10 to
192.0.2.20. Host A requests an address and gets 192.0.2.10. Now the system
administrator decides to reserve address 192.0.2.10 for Host B. In
general, reserving an address that is currently assigned to someone else
is not recommended, but there are valid use cases where such an operation
is warranted.
The server now has a conflict to resolve. Let's analyze the situation
here. If Host B boots up and requests an address, the server is not able
to assign the reserved address 192.0.2.10. A naive approach would to be
immediately remove the existing lease for the Host A and create a new one
for the Host B. That would not solve the problem, though, because as soon
as the Host B gets the address, it will detect that the address is already
in use by the Host A and would send the DHCPDECLINE message. Therefore, in
this situation, the server has to temporarily assign a different address
(not matching what has been reserved) to the Host B.
When Host A renews its address, the server will discover that the address
being renewed is now reserved for another host - Host B. Therefore the
server will inform the Host A that it is no longer allowed to use it by
sending a DHCPNAK message. The server will not remove the lease, though,
as there's small chance that the DHCPNAK may be lost if the network is
lossy. If that happens, the client will not receive any responses, so it
will retransmit its DHCPREQUEST packet. Once the DHCPNAK is received by
Host A, it will revert to the server discovery and will eventually get a
different address. Besides allocating a new lease, the server will also
remove the old one. As a result, address 192.0.2.10 will become free .
When Host B tries to renew its temporarily assigned address, the server
will detect that it has a valid lease, but there is a reservation for a
different address. The server will send DHCPNAK to inform Host B that its
address is no longer usable, but will keep its lease (again, the DHCPNAK
may be lost, so the server will keep it, until the client returns for a
new address). Host B will revert to the server discovery phase and will
eventually send a DHCPREQUEST message. This time the server will find out
that there is a reservation for that host and the reserved address
192.0.2.10 is not used, so it will be granted. It will also remove the
lease for the temporarily assigned address that Host B previously
obtained.
This recovery will succeed, even if other hosts will attempt to get the
reserved address. Had the Host C requested address 192.0.2.10 after the
reservation was made, the server will either offer a different address
(when responding to DHCPDISCOVER) or would send DHCPNAK (when responding
to DHCPREQUEST).
This recovery mechanism allows the server to fully recover from a case
where reservations conflict with the existing leases. This procedure takes
time and will roughly take as long as the value set for of renew-timer.
The best way to avoid such recovery is to not define new reservations that
conflict with existing leases. Another recommendation is to use
out-of-pool reservations. If the reserved address does not belong to a
pool, there is no way that other clients could get this address.
8.3.3. Reserving a Hostname
When the reservation for a client includes the hostname, the server will
return this hostname to the client in the Client FQDN or Hostname options.
The server responds with the Client FQDN option only if the client has
included Client FQDN option in its message to the server. The server will
respond with the Hostname option if the client included Hostname option in
its message to the server or when the client requested Hostname option
using Parameter Request List option. The server will return the Hostname
option even if it is not configured to perform DNS updates. The reserved
hostname always takes precedence over the hostname supplied by the client
or the autogenerated (from the IPv4 address) hostname.
The server qualifies the reserved hostname with the value of the
qualifying-suffix parameter. For example, the following subnet
configuration:
{
"subnet4": [ {
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"hostname": "alice-laptop"
}
]
}],
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example.isc.org."
}
}
will result in assigning the "alice-laptop.example.isc.org." hostname to
the client using the MAC address "aa:bb:cc:dd:ee:ff". If the
qualifying-suffix is not specified, the default (empty) value will be
used, and in this case the value specified as a hostname will be treated
as fully qualified name. Thus, by leaving the qualifying-suffix empty it
is possible to qualify hostnames for the different clients with different
domain names:
{
"subnet4": [ {
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"hostname": "alice-laptop.isc.org."
},
{
"hw-address": "12:34:56:78:99:AA",
"hostname": "mark-desktop.example.org."
}
]
}],
"dhcp-ddns": {
"enable-updates": true,
}
}
8.3.4. Including Specific DHCPv4 Options in Reservations
Kea 1.1.0 introduced the ability to specify options on a per host basis.
The options follow the same rules as any other options. These can be
standard options (see Section 8.2.8, "Standard DHCPv4 Options"), custom
options (see Section 8.2.9, "Custom DHCPv4 options") or vendor specific
options (see Section 8.2.11, "DHCPv4 Vendor Specific Options"). The
following example demonstrates how standard options can be defined.
{
"subnet4": [ {
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"ip-address": "192.0.2.1",
"option-data": [
{
"name": "cookie-servers",
"data": "10.1.1.202,10.1.1.203"
},
{
"name": "log-servers",
"data": "10.1.1.200,10.1.1.201"
} ]
} ]
} ]
}
Vendor specific options can be reserved in a similar manner:
{
"subnet4": [ {
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"ip-address": "10.0.0.7",
"option-data": [
{
"name": "vivso-suboptions",
"data": "4491"
},
{
"name": "tftp-servers",
"space": "vendor-4491",
"data": "10.1.1.202,10.1.1.203"
} ]
} ]
} ]
}
Options defined on host level have the highest priority. In other words,
if there are options defined with the same type on global, subnet, class
and host level, the host specific values will be used.
8.3.5. Reserving Next Server, Server Hostname and Boot File Name
BOOTP/DHCPv4 messages include "siaddr", "sname" and "file" fields. Even
though, DHCPv4 includes corresponding options, such as option 66 and
option 67, some clients may not support these options. For this reason,
server administrators often use the "siaddr", "sname" and "file" fields
instead.
With Kea, it is possible to make static reservations for these DHCPv4
message fields:
{
"subnet4": [ {
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"next-server": "10.1.1.2",
"server-hostname": "server-hostname.example.org",
"boot-file-name": "/tmp/bootfile.efi"
} ]
} ]
}
Note that those parameters can be specified in combination with other
parameters for a reservation, e.g. reserved IPv4 address. These parameters
are optional, i.e. a subset of them can specified, or all of them can be
omitted.
8.3.6. Reserving Client Classes in DHCPv4
Section 13.3, "Using Expressions In Classification" explains how to
configure the server to assign classes to a client based on the content of
the options that this client sends to the server. Host reservations
mechanisms also allow for statically assigning classes to the clients. The
definitions of these classes should exist in the Kea configuration. The
following configuration snippet shows how to specify that a client belongs
to classes reserved-class1 and reserved-class2. Those classes are
associated with specific options being sent to the clients which belong to
them.
{
"client-classes": [
{
"name": "reserved-class1",
"option-data": [
{
"name": "routers",
"data": "10.0.0.200"
}
]
},
{
"name": "reserved-class2",
"option-data": [
{
"name": "domain-name-servers",
"data": "10.0.0.201"
}
]
}
],
"subnet4": [ {
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"client-classes": [ "reserved-class1", "reserved-class2" ]
}
]
} ]
}
Static class assignments, as shown above, can be used in conjunction with
classification using expressions. The "KNOWN" or "UNKNOWN" builtin class
is added to the packet and any class depending on it directly or
indirectly and not only-if-required is evaluated.
Note
If you want to force the evaluation of a class expression after the host
reservation lookup, for instance because of a dependency on
"reserved-class1" from the previous example, you should add a
"member('KNOWN')" in the expression.
8.3.7. Storing Host Reservations in MySQL, PostgreSQL or Cassandra
It is possible to store host reservations in MySQL, PostgreSQL or
Cassandra. See Section 9.2.3, "Hosts Storage" for information on how to
configure Kea to use reservations stored in MySQL, PostgreSQL or
Cassandra. Kea provides dedicated hook for managing reservations in a
database, section Section 14.4.4, "host_cmds: Host Commands" provide
detailed information. http://kea.isc.org/wiki/HostReservationsHowTo
provides some examples how to conduct common host reservation operations.
Note
In Kea maximum length of an option specified per host is arbitrarily set
to 4096 bytes.
8.3.8. Fine Tuning DHCPv4 Host Reservation
The host reservation capability introduces additional restrictions for the
allocation engine (the component of Kea that selects an address for a
client) during lease selection and renewal. In particular, three major
checks are necessary. First, when selecting a new lease, it is not
sufficient for a candidate lease to not be used by another DHCP client. It
also must not be reserved for another client. Second, when renewing a
lease, additional check must be performed whether the address being
renewed is not reserved for another client. Finally, when a host renews an
address, the server has to check whether there is a reservation for this
host, so the existing (dynamically allocated) address should be revoked
and the reserved one be used instead.
Some of those checks may be unnecessary in certain deployments and not
performing them may improve performance. The Kea server provides the
reservation-mode configuration parameter to select the types of
reservations allowed for the particular subnet. Each reservation type has
different constraints for the checks to be performed by the server when
allocating or renewing a lease for the client. Allowed values are:
* all - enables all host reservation types. This is the default value.
This setting is the safest and the most flexible. It allows in-pool
and out-of-pool reservations. As all checks are conducted, it is also
the slowest.
* out-of-pool - allows only out of pool host reservations. With this
setting in place, the server may assume that all host reservations are
for addresses that do not belong to the dynamic pool. Therefore it can
skip the reservation checks when dealing with in-pool addresses, thus
improving performance. Do not use this mode if any of your
reservations use in-pool address. Caution is advised when using this
setting: Kea does not sanity check the reservations against
reservation-mode and misconfiguration may cause problems.
* disabled - host reservation support is disabled. As there are no
reservations, the server will skip all checks. Any reservations
defined will be completely ignored. As the checks are skipped, the
server may operate faster in this mode.
An example configuration that disables reservation looks like follows:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"reservation-mode": "disabled",
...
}
]
}
Another aspect of the host reservations are the different types of
identifiers. Kea 1.1.0 supports four types of identifiers (hw-address,
duid, client-id and circuit-id), but more identifier types are likely to
be added in the future. This is beneficial from a usability perspective.
However, there is a drawback. For each incoming packet Kea has to to
extract each identifier type and then query the database to see if there
is a reservation done by this particular identifier. If nothing is found,
the next identifier is extracted and the next query is issued. This
process continues until either a reservation is found or all identifier
types have been checked. Over time with an increasing number of supported
identifier types, Kea would become slower and slower.
To address this problem, a parameter called host-reservation-identifiers
has been introduced. It takes a list of identifier types as a parameter.
Kea will check only those identifier types enumerated in
host-reservation-identifiers. From a performance perspective the number of
identifier types should be kept to a minimum, ideally limited to one. If
your deployment uses several reservation types, please enumerate them from
most to least frequently used as this increases the chances of Kea finding
the reservation using the fewest number of queries. An example of host
reservation identifiers looks as follows:
"host-reservation-identifiers": [ "circuit-id", "hw-address", "duid", "client-id" ],
"subnet4": [
{
"subnet": "192.0.2.0/24",
...
}
]
If not specified, the default value is:
"host-reservation-identifiers": [ "hw-address", "duid", "circuit-id", "client-id" ]
8.4. Shared networks in DHCPv4
DHCP servers use subnet information in two ways. First, it is used to
determine the point of attachment, or simply put, where the client is
connected to the network. Second, the subnet information is used to group
information pertaining to specific location in the network. This approach
works well in general case, but the are scenarios where the boundaries are
blurred. Sometimes it is useful to have more than one logical IP subnet
being deployed on the same physical link. The need to understand that two
or more subnets are used on the same link requires additional logic in the
DHCP server. This capability has been added in Kea 1.3.0. It is called
"shared networks" in Kea and ISC DHCP projects. It is sometimes also
called "shared subnets". In Microsoft's nomenclature it is called
"multinet".
There are many use cases where the feature is useful. This paragraph
explains just a handful of the most common ones. The first and by far the
most common use case is an existing network that has grown and is running
out of available address space. Rather than migrating all devices to a
new, larger subnet, it is easier to simply configure additional subnet on
top of the existing one. Sometimes, due to address space fragmentation
(e.g. only many disjoint /24s are available) this is the only choice.
Also, configuring additional subnet has the advantage of not disrupting
the operation of existing devices.
Another very frequent use case comes from cable networks. There are two
types of devices in cable networks: cable modems and the end user devices
behind them. It is a common practice to use different subnet for cable
modems to prevent users from tinkering with their cable modems. In this
case, the distinction is based on the type of device, rather than address
space exhaustion.
A client connected to a shared network may be assigned an address from any
of the address pools defined within the subnets belonging to the shared
network. Internally, the server selects one of the subnets belonging to a
shared network and tries to allocate an address from this subnet. If the
server is unable to allocate an address from the selected subnet (e.g. due
to address pools exhaustion) it will use another subnet from the same
shared network and try to allocate an address from this subnet etc.
Therefore, in the typical case, the server will allocate all addresses
available for a given subnet before it starts allocating addresses from
other subnets belonging to the same shared network. However, in certain
situations the client can be allocated an address from the other subnets
before the address pools in the first subnet get exhausted, e.g. when the
client provides a hint that belongs to another subnet or the client has
reservations in a different than default subnet.
Note
It is strongly discouraged for the Kea deployments to assume that the
server doesn't allocate addresses from other subnets until it uses all the
addresses from the first subnet in the shared network. Apart from the fact
that hints, host reservations and client classification affect subnet
selection, it is also foreseen that we will enhance allocation strategies
for shared networks in the future versions of Kea, so as the selection of
subnets within a shared network is equally probable (unpredictable).
In order to define a shared network an additional configuration scope is
introduced:
{
"Dhcp4": {
"shared-networks": [
{
// Name of the shared network. It may be an arbitrary string
// and it must be unique among all shared networks.
"name": "my-secret-lair-level-1",
// Subnet selector can be specifed on the shared network level.
// Subnets from this shared network will be selected for directly
// connected clients sending requests to server's "eth0" interface.
"interface": "eth0",
// This starts a list of subnets in this shared network.
// There are two subnets in this example.
"subnet4": [
{
"subnet": "10.0.0.0/8",
"pools": [ { "pool": "10.0.0.1 - 10.0.0.99" } ],
},
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.100 - 192.0.2.199" } ]
}
],
} ], // end of shared-networks
// It is likely that in your network you'll have a mix of regular,
// "plain" subnets and shared networks. It is perfectly valid to mix
// them in the same config file.
//
// This is regular subnet. It's not part of any shared-network.
"subnet4": [
{
"subnet": "192.0.3.0/24",
"pools": [ { "pool": "192.0.3.1 - 192.0.3.200" } ],
"interface": "eth1"
}
]
} // end of Dhcp4
}
As you see in the example, it is possible to mix shared and regular
("plain") subnets. Each shared network must have a unique name. This is
similar to ID for subnets, but gives you more flexibility. This is used
for logging, but also internally for identifying shared networks.
In principle it makes sense to define only shared networks that consist of
two or more subnets. However, for testing purposes it is allowed to define
a shared network with just one subnet or even an empty one. This is not a
recommended practice in production networks, as the shared network logic
requires additional processing and thus lowers server's performance. To
avoid unnecessary performance degradation the shared subnets should only
be defined when required by the deployment.
Shared networks provide an ability to specify many parameters in the
shared network scope that will apply to all subnets within it. If
necessary, you can specify a parameter on the shared network scope and
then override its value in the subnet scope. For example:
"shared-networks": [
{
"name": "lab-network3",
"interface": "eth0",
// This applies to all subnets in this shared network, unless
// values are overridden on subnet scope.
"valid-lifetime": 600,
// This option is made available to all subnets in this shared
// network.
"option-data": [ {
"name": "log-servers",
"data": "1.2.3.4"
} ],
"subnet4": [
{
"subnet": "10.0.0.0/8",
"pools": [ { "pool": "10.0.0.1 - 10.0.0.99" } ],
// This particular subnet uses different values.
"valid-lifetime": 1200,
"option-data": [
{
"name": "log-servers",
"data": "10.0.0.254"
},
{
"name": "routers",
"data": "10.0.0.254"
} ]
},
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.100 - 192.0.2.199" } ],
// This subnet does not specify its own valid-lifetime value,
// so it is inherited from shared network scope.
"option-data": [
{
"name": "routers",
"data": "192.0.2.1"
} ]
}
]
} ]
In this example, there is a log-servers option defined that is available
to clients in both subnets in this shared network. Also, a valid lifetime
is set to 10 minutes (600s). However, the first subnet overrides some of
the values (valid lifetime is 20 minutes, different IP address for
log-servers), but also adds its own option (router address). Assuming a
client asking for router and log servers options is assigned a lease from
this subnet, he will get a lease for 20 minutes and log-servers and
routers value of 10.0.0.254. If the same client is assigned to the second
subnet, he will get a 10 minutes long lease, log-servers value of 1.2.3.4
and routers set to 192.0.2.1.
8.4.1. Local and relayed traffic in shared networks
It is possible to specify interface name in the shared network scope to
tell the server that this specific shared network is reachable directly
(not via relays) using local network interface. It is sufficient to
specify it once on the shared network level. As all subnets in a shared
network are expected to be used on the same physical link, it is a
configuration error to attempt to define a shared network using subnets
that are reachable over different interfaces. It is allowed to specify
interface parameter on each subnet, although its value must be the same
for each subnet. Thus it's usually more convenient to specify it once on
the shared network level.
"shared-networks": [
{
"name": "office-floor-2",
// This tells Kea that the whole shared networks is reachable over
// local interface. This applies to all subnets in this network.
"interface": "eth0",
"subnet4": [
{
"subnet": "10.0.0.0/8",
"pools": [ { "pool": "10.0.0.1 - 10.0.0.99" } ],
"interface": "eth0"
},
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.100 - 192.0.2.199" } ]
// Specifying a different interface name is configuration
// error:
// "interface": "eth1"
}
]
} ]
Somewhat similar to interface names, also relay IP addresses can be
specified for the whole shared network. However, depending on your relay
configuration, it may use different IP addresses depending on which subnet
is being used. Thus there is no requirement to use the same IP relay
address for each subnet. Here's an example:
"shared-networks": [
{
"name": "kakapo",
"relay": {
"ip-addresses": [ "192.3.5.6" ]
},
"subnet4": [
{
"subnet": "192.0.2.0/26",
"relay": {
"ip-addresses": [ "192.1.1.1" ]
},
"pools": [ { "pool": "192.0.2.63 - 192.0.2.63" } ]
},
{
"subnet": "10.0.0.0/24",
"relay": {
"ip-addresses": [ "192.2.2.2" ]
},
"pools": [ { "pool": "10.0.0.16 - 10.0.0.16" } ]
}
]
}
]
In this particular case the relay IP address specified on network level
doesn't have much sense, as it is overridden in both subnets, but it was
left there as an example of how one could be defined on network level.
Note that the relay agent IP address typically belongs to the subnet it
relays packets from, but this is not a strict requirement. Therefore Kea
accepts any value here as long as it is valid IPv4 address.
8.4.2. Client classification in shared networks
Sometimes it is desired to segregate clients into specific subnets based
on some properties. This mechanism is called client classification and is
described in Chapter 13, Client Classification. Client classification can
be applied to subnets belonging to shared networks in the same way as it
is used for subnets specified outside of shared networks. It is important
to understand how the server selects subnets for the clients when client
classification is in use, to assure that the desired subnet is selected
for a given client type.
If a subnet is associated with some classes, only the clients belonging to
any of these classes can use this subnet. If there are no classes
specified for a subnet, any client connected to a given shared network can
use this subnet. A common mistake is to assume that the subnet including
client classes is preferred over subnets without client classes. Consider
the following example:
{
"client-classes": [
{
"name": "b-devices",
"test": "option[93].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"interface": "eth0",
"subnet4": [
{
"subnet": "192.0.2.0/26",
"pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
},
{
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
"client-class": "b-devices"
}
]
}
]
}
If the client belongs to "b-devices" class (because it includes option 93
with a value of 0x0002) it doesn't guarantee that the subnet 10.0.0.0/24
will be used (or preferred) for this client. The server can use any of the
two subnets because the subnet 192.0.2.0/26 is also allowed for this
client. The client classification used in this case should be pereceived
as a way to restrict access to certain subnets, rather than a way to
express subnet preference. For example, if the client doesn't belong to
the "b-devices" class it may only use the subnet 192.0.2.0/26 and will
never use the subnet 10.0.0.0/24.
A typical use case for client classification is in the cable network,
where cable modems should use one subnet and other devices should use
another subnet within the same shared network. In this case it is required
to apply classification on all subnets. The following example defines two
classes of devices. The subnet selection is made based on option 93
values.
{
"client-classes": [
{
"name": "a-devices",
"test": "option[93].hex == 0x0001"
},
{
"name": "b-devices",
"test": "option[93].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"interface": "eth0",
"subnet4": [
{
"subnet": "192.0.2.0/26",
"pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
"client-class": "a-devices"
},
{
"subnet": "10.0.0.0/24",
"pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
"client-class": "b-devices"
}
]
}
]
}
In this example each class has its own restriction. Only clients that
belong to class "a-devices" will be able to use subnet 192.0.2.0/26 and
only clients belonging to b-devices will be able to use subnet
10.0.0.0/24. Care should be taken to not define too restrictive
classification rules, as clients that are unable to use any subnets will
be refused service. Although, this may be a desired outcome if one desires
to service only clients of known properties (e.g. only VoIP phones allowed
on a given link).
Note that it is possible to achieve similar effect as presented in this
section without the use of shared networks. If the subnets are placed in
the global subnets scope, rather than in the shared network, the server
will still use classification rules to pick the right subnet for a given
class of devices. The major benefit of placing subnets within the shared
network is that common parameters for the logically grouped subnets can be
specified once, in the shared network scope, e.g. "interface" or "relay"
parameter. All subnets belonging to this shared network will inherit those
parameters.
8.4.3. Host reservations in shared networks
Subnets being part of a shared network allow host reservations, similar to
regular subnets:
{
"shared-networks": [
{
"name": "frog",
"interface": "eth0",
"subnet4": [
{
"subnet": "192.0.2.0/26",
"id": 100,
"pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"ip-address": "192.0.2.28"
}
]
},
{
"subnet": "10.0.0.0/24",
"id": 101,
"pools": [ { "pool": "10.0.0.1 - 10.0.0.254" } ],
"reservations": [
{
"hw-address": "11:22:33:44:55:66",
"ip-address": "10.0.0.29"
}
]
}
]
}
]
}
It is worth noting that Kea conducts additional checks when processing a
packet if shared networks are defined. First, instead of simply checking
if there's a reservation for a given client in his initially selected
subnet, it goes through all subnets in a shared network looking for a
reservation. This is one of the reasons why defining a shared network may
impact performance. If there is a reservation for a client in any subnet,
that particular subnet will be picked for the client. Although it's
technically not an error, it is considered a bad practice to define
reservations for the same host in multiple subnets belonging to the same
shared network.
While not strictly mandatory, it is strongly recommended to use explicit
"id" values for subnets if you plan to use database storage for host
reservations. If ID is not specified, the values for it be autogenerated,
i.e. it will assign increasing integer values starting from 1. Thus, the
autogenerated IDs are not stable across configuration changes.
8.5. Server Identifier in DHCPv4
The DHCPv4 protocol uses a "server identifier" to allow clients to
discriminate between several servers present on the same link: this value
is an IPv4 address of the server. The server chooses the IPv4 address of
the interface on which the message from the client (or relay) has been
received. A single server instance will use multiple server identifiers if
it is receiving queries on multiple interfaces.
It is possible to override default server identifier values by specifying
"dhcp-server-identifier" option. This option is only supported on the
global, shared network and subnet level. It must not be specified on
client class and host reservation level.
The following example demonstrates how to override server identifier for a
subnet:
"subnet4": [
{
"subnet": "192.0.2.0/24",
"option-data": [
{
"name": "dhcp-server-identifier",
"data": "10.2.5.76"
}
],
...
}
]
8.6. How the DHCPv4 Server Selects a Subnet for the Client
The DHCPv4 server differentiates between the directly connected clients,
clients trying to renew leases and clients sending their messages through
relays. For directly connected clients, the server will check the
configuration for the interface on which the message has been received
and, if the server configuration doesn't match any configured subnet, the
message is discarded.
Assuming that the server's interface is configured with the IPv4 address
192.0.2.3, the server will only process messages received through this
interface from a directly connected client if there is a subnet configured
to which this IPv4 address belongs, e.g. 192.0.2.0/24. The server will use
this subnet to assign IPv4 address for the client.
The rule above does not apply when the client unicasts its message, i.e.
is trying to renew its lease. Such a message is accepted through any
interface. The renewing client sets ciaddr to the currently used IPv4
address. The server uses this address to select the subnet for the client
(in particular, to extend the lease using this address).
If the message is relayed it is accepted through any interface. The giaddr
set by the relay agent is used to select the subnet for the client.
It is also possible to specify a relay IPv4 address for a given subnet. It
can be used to match incoming packets into a subnet in uncommon
configurations, e.g. shared networks. See Section 8.6.1, "Using a Specific
Relay Agent for a Subnet" for details.
Note
The subnet selection mechanism described in this section is based on the
assumption that client classification is not used. The classification
mechanism alters the way in which a subnet is selected for the client,
depending on the classes to which the client belongs.
8.6.1. Using a Specific Relay Agent for a Subnet
A relay has to have an interface connected to the link on which the
clients are being configured. Typically the relay has an IPv4 address
configured on that interface that belongs to the subnet from which the
server will assign addresses. In the typical case, the server is able to
use the IPv4 address inserted by the relay (in the giaddr field of the
DHCPv4 packet) to select the appropriate subnet.
However, that is not always the case. In certain uncommon -- but valid --
deployments, the relay address may not match the subnet. This usually
means that there is more than one subnet allocated for a given link. The
two most common examples where this is the case are long lasting network
renumbering (where both old and new address space is still being used) and
a cable network. In a cable network both cable modems and the devices
behind them are physically connected to the same link, yet they use
distinct addressing. In such a case, the DHCPv4 server needs additional
information (the IPv4 address of the relay) to properly select an
appropriate subnet.
The following example assumes that there is a subnet 192.0.2.0/24 that is
accessible via a relay that uses 10.0.0.1 as its IPv4 address. The server
will be able to select this subnet for any incoming packets that came from
a relay that has an address in 192.0.2.0/24 subnet. It will also select
that subnet for a relay with address 10.0.0.1.
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"relay": {
"ip-addresses": [ "10.0.0.1" ]
},
...
}
],
...
}
If "relay" is specified, the "ip-addresses" parameter within it is
mandatory.
Note
As of Kea 1.4, the "ip-address" parameter has been deprecated in favor of
"ip-addresses" which supports specifying a list of addresses.
Configuration parsing, will honor the singular form for now but users are
encouraged to migrate.
8.6.2. Segregating IPv4 Clients in a Cable Network
In certain cases, it is useful to mix relay address information,
introduced in Section 8.6.1, "Using a Specific Relay Agent for a Subnet"
with client classification, explained in Chapter 13, Client
Classification. One specific example is cable network, where typically
modems get addresses from a different subnet than all devices connected
behind them.
Let us assume that there is one CMTS (Cable Modem Termination System) with
one CM MAC (a physical link that modems are connected to). We want the
modems to get addresses from the 10.1.1.0/24 subnet, while everything
connected behind modems should get addresses from another subnet
(192.0.2.0/24). The CMTS that acts as a relay uses address 10.1.1.1. The
following configuration can serve that configuration:
"Dhcp4": {
"subnet4": [
{
"subnet": "10.1.1.0/24",
"pools": [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
"client-class" "docsis3.0",
"relay": {
"ip-addresses": [ "10.1.1.1 ]"
}
},
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"relay": {
"ip-addresses": [ "10.1.1.1" ]
}
}
],
...
}
8.7. Duplicate Addresses (DHCPDECLINE Support)
The DHCPv4 server is configured with a certain pool of addresses that it
is expected to hand out to the DHCPv4 clients. It is assumed that the
server is authoritative and has complete jurisdiction over those
addresses. However, due to various reasons, such as misconfiguration or a
faulty client implementation that retains its address beyond the valid
lifetime, there may be devices connected that use those addresses without
the server's approval or knowledge.
Such an unwelcome event can be detected by legitimate clients (using ARP
or ICMP Echo Request mechanisms) and reported to the DHCPv4 server using a
DHCPDECLINE message. The server will do a sanity check (if the client
declining an address really was supposed to use it), and then will conduct
a clean up operation. Any DNS entries related to that address will be
removed, the fact will be logged and hooks will be triggered. After that
is done, the address will be marked as declined (which indicates that it
is used by an unknown entity and thus not available for assignment to
anyone) and a probation time will be set on it. Unless otherwise
configured, the probation period lasts 24 hours. After that period, the
server will recover the lease (i.e. put it back into the available state)
and the address will be available for assignment again. It should be noted
that if the underlying issue of a misconfigured device is not resolved,
the duplicate address scenario will repeat. On the other hand, it provides
an opportunity to recover from such an event automatically, without any
sysadmin intervention.
To configure the decline probation period to a value other than the
default, the following syntax can be used:
"Dhcp4": {
"decline-probation-period": 3600,
"subnet4": [ ... ],
...
}
The parameter is expressed in seconds, so the example above will instruct
the server to recycle declined leases after an hour.
There are several statistics and hook points associated with the Decline
handling procedure. The lease4_decline hook is triggered after the
incoming DHCPDECLINE message has been sanitized and the server is about to
decline the lease. The declined-addresses statistic is increased after the
hook returns (both global and subnet specific variants). (See Section 8.8,
"Statistics in the DHCPv4 Server" and Chapter 14, Hooks Libraries for more
details on DHCPv4 statistics and Kea hook points.)
Once the probation time elapses, the declined lease is recovered using the
standard expired lease reclamation procedure, with several additional
steps. In particular, both declined-addresses statistics (global and
subnet specific) are decreased. At the same time,
reclaimed-declined-addresses statistics (again in two variants, global and
subnet specific) are increased.
Note about statistics: The server does not decrease the assigned-addresses
statistics when a DHCPDECLINE is received and processed successfully.
While technically a declined address is no longer assigned, the primary
usage of the assigned-addresses statistic is to monitor pool utilization.
Most people would forget to include declined-addresses in the calculation,
and simply do assigned-addresses/total-addresses. This would have a bias
towards under-representing pool utilization. As this has a potential for
major issues, we decided not to decrease assigned addresses immediately
after receiving DHCPDECLINE, but to do it later when we recover the
address back to the available pool.
8.8. Statistics in the DHCPv4 Server
Note
This section describes DHCPv4-specific statistics. For a general overview
and usage of statistics, see Chapter 15, Statistics.
The DHCPv4 server supports the following statistics:
Table 8.4. DHCPv4 Statistics
+-----------------------------------------------------------------------------+
| Statistic |Data Type|Description |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPv4 packets |
| | |received. This includes all|
| pkt4-received | integer |packets: valid, bogus, |
| | |corrupted, rejected etc. |
| | |This statistic is expected |
| | |to grow rapidly. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPDISCOVER |
| | |packets received. This |
| | |statistic is expected to |
| | |grow. Its increase means |
| pkt4-discover-received | integer |that clients that just |
| | |booted started their |
| | |configuration process and |
| | |their initial packets |
| | |reached your server. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPOFFER packets|
| | |received. This statistic is|
| | |expected to remain zero at |
| | |all times, as DHCPOFFER |
| | |packets are sent by the |
| | |server and the server is |
| | |never expected to receive |
| pkt4-offer-received | integer |them. Non-zero value |
| | |indicates an error. One |
| | |likely cause would be a |
| | |misbehaving relay agent |
| | |that incorrectly forwards |
| | |DHCPOFFER messages towards |
| | |the server, rather back to |
| | |the clients. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPREQUEST |
| | |packets received. This |
| | |statistic is expected to |
| | |grow. Its increase means |
| pkt4-request-received | integer |that clients that just |
| | |booted received server's |
| | |response (DHCPOFFER), |
| | |accepted it and now |
| | |requesting an address |
| | |(DHCPREQUEST). |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPACK packets |
| | |received. This statistic is|
| | |expected to remain zero at |
| | |all times, as DHCPACK |
| | |packets are sent by the |
| | |server and the server is |
| | |never expected to receive |
| pkt4-ack-received | integer |them. Non-zero value |
| | |indicates an error. One |
| | |likely cause would be a |
| | |misbehaving relay agent |
| | |that incorrectly forwards |
| | |DHCPACK messages towards |
| | |the server, rather back to |
| | |the clients. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPNAK packets |
| | |received. This statistic is|
| | |expected to remain zero at |
| | |all times, as DHCPNAK |
| | |packets are sent by the |
| | |server and the server is |
| | |never expected to receive |
| pkt4-nak-received | integer |them. Non-zero value |
| | |indicates an error. One |
| | |likely cause would be a |
| | |misbehaving relay agent |
| | |that incorrectly forwards |
| | |DHCPNAK messages towards |
| | |the server, rather back to |
| | |the clients. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPRELEASE |
| | |packets received. This |
| | |statistic is expected to |
| pkt4-release-received | integer |grow. Its increase means |
| | |that clients that had an |
| | |address are shutting down |
| | |or stop using their |
| | |addresses. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPDECLINE |
| | |packets received. This |
| | |statistic is expected to |
| | |remain close to zero. Its |
| | |increase means that a |
| pkt4-decline-received | integer |client that leased an |
| | |address, but discovered |
| | |that the address is |
| | |currently used by an |
| | |unknown device in your |
| | |network. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPINFORM |
| | |packets received. This |
| | |statistic is expected to |
| | |grow. Its increase means |
| pkt4-inform-received | integer |that there are clients that|
| | |either do not need an |
| | |address or already have an |
| | |address and are interested |
| | |only in getting additional |
| | |configuration parameters. |
|---------------------------------------+---------+---------------------------|
| | |Number of packets received |
| | |of an unknown type. |
| | |Non-zero value of this |
| | |statistic indicates that |
| pkt4-unknown-received | integer |the server received a |
| | |packet that it wasn't able |
| | |to recognize: either with |
| | |unsupported type or |
| | |possibly malformed (without|
| | |message type option). |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPv4 packets |
| | |sent. This statistic is |
| | |expected to grow every time|
| | |the server transmits a |
| | |packet. In general, it |
| | |should roughly match |
| pkt4-sent | integer |pkt4-received, as most |
| | |incoming packets cause |
| | |server to respond. There |
| | |are exceptions (e.g. |
| | |DHCPRELEASE), so do not |
| | |worry, if it is lesser than|
| | |pkt4-received. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPOFFER packets|
| | |sent. This statistic is |
| | |expected to grow in most |
| | |cases after a DHCPDISCOVER |
| | |is processed. There are |
| pkt4-offer-sent | integer |certain uncommon, but valid|
| | |cases where incoming |
| | |DHCPDISCOVER is dropped, |
| | |but in general this |
| | |statistic is expected to be|
| | |close to |
| | |pkt4-discover-received. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPACK packets |
| | |sent. This statistic is |
| | |expected to grow in most |
| | |cases after a DHCPREQUEST |
| | |is processed. There are |
| pkt4-ack-sent | integer |certain cases where DHCPNAK|
| | |is sent instead. In |
| | |general, the sum of |
| | |pkt4-ack-sent and |
| | |pkt4-nak-sent should be |
| | |close to |
| | |pkt4-request-received. |
|---------------------------------------+---------+---------------------------|
| | |Number of DHCPNAK packets |
| | |sent. This statistic is |
| | |expected to grow when the |
| | |server chooses to not honor|
| pkt4-nak-sent | integer |the address requested by a |
| | |client. In general, the sum|
| | |of pkt4-ack-sent and |
| | |pkt4-nak-sent should be |
| | |close to |
| | |pkt4-request-received. |
|---------------------------------------+---------+---------------------------|
| | |Number of incoming packets |
| | |that could not be parsed. A|
| | |non-zero value of this |
| | |statistic indicates that |
| pkt4-parse-failed | integer |the server received |
| | |malformed or truncated |
| | |packet. This may indicate |
| | |problems in your network, |
| | |faulty clients or a bug in |
| | |the server. |
|---------------------------------------+---------+---------------------------|
| | |Number of incoming packets |
| | |that were dropped. The |
| | |exact reason for dropping |
| | |packets is logged, but the |
| | |most common reasons may be:|
| pkt4-receive-drop | integer |an unacceptable packet |
| | |type, direct responses are |
| | |forbidden, or the server-id|
| | |sent by the client does not|
| | |match the server's |
| | |server-id. |
|---------------------------------------+---------+---------------------------|
| | |The total number of |
| | |addresses available for |
| | |DHCPv4 management. In other|
| | |words, this is the sum of |
| | |all addresses in all |
| | |configured pools. This |
| | |statistic changes only |
| | |during configuration |
| | |changes. Note it does not |
| subnet[id].total-addresses | integer |take into account any |
| | |addresses that may be |
| | |reserved due to host |
| | |reservation. The id is the |
| | |subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately. This statistic |
| | |is reset during |
| | |reconfiguration event. |
|---------------------------------------+---------+---------------------------|
| | |This statistic shows the |
| | |number of assigned |
| | |addresses in a given |
| | |subnet. It increases every |
| | |time a new lease is |
| | |allocated (as a result of |
| | |receiving a DHCPREQUEST |
| | |message) and is decreased |
| subnet[id].assigned-addresses | integer |every time a lease is |
| | |released (a DHCPRELEASE |
| | |message is received) or |
| | |expires. The id is the |
| | |subnet-id of the subnet. |
| | |This statistic is exposed |
| | |for each subnet separately.|
| | |This statistic is reset |
| | |during reconfiguration |
| | |event. |
|---------------------------------------+---------+---------------------------|
| | |This statistic is the |
| | |number of expired leases |
| | |that have been reclaimed |
| reclaimed-leases | integer |since server startup. It is|
| | |incremented each time an |
| | |expired lease is reclaimed |
| | |and is reset when the |
| | |server is reconfigured. |
|---------------------------------------+---------+---------------------------|
| | |This statistic is the |
| | |number of expired leases |
| | |associated with a given |
| | |subnet (id is the |
| | |subnet-id) that have been |
| subnet[id].reclaimed-leases | integer |reclaimed since server |
| | |startup. It is incremented |
| | |each time an expired lease |
| | |is reclaimed and is reset |
| | |when the server is |
| | |reconfigured. |
|---------------------------------------+---------+---------------------------|
| | |This statistic shows the |
| | |number of IPv4 addresses |
| | |that are currently |
| | |declined, so counting the |
| | |number of leases currently |
| | |unavailable. Once a lease |
| | |is recovered, this |
| | |statistic will be |
| | |decreased. Ideally, this |
| declined-addresses | integer |statistic should be zero. |
| | |If this statistic is |
| | |non-zero (or worse |
| | |increasing), a network |
| | |administrator should |
| | |investigate if there is a |
| | |misbehaving device in his |
| | |network. This is a global |
| | |statistic that covers all |
| | |subnets. |
|---------------------------------------+---------+---------------------------|
| | |This statistic shows the |
| | |number of IPv4 addresses |
| | |that are currently declined|
| | |in a given subnet, so is a |
| | |count of the number of |
| | |leases currently |
| | |unavailable. Once a lease |
| | |is recovered, this |
| | |statistic will be |
| | |decreased. Ideally, this |
| subnet[id].declined-addresses | integer |statistic should be zero. |
| | |If this statistic is |
| | |non-zero (or worse |
| | |increasing), a network |
| | |administrator should |
| | |investigate if there is a |
| | |misbehaving device in his |
| | |network. The id is the |
| | |subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately. |
|---------------------------------------+---------+---------------------------|
| | |This statistic shows the |
| | |number of IPv4 addresses |
| | |that were declined, but |
| | |have now been recovered. |
| | |Unlike declined-addresses, |
| | |this statistic never |
| reclaimed-declined-addresses | integer |decreases. It can be used |
| | |as a long term indicator of|
| | |how many actual valid |
| | |Declines were processed and|
| | |recovered from. This is a |
| | |global statistic that |
| | |covers all subnets. |
|---------------------------------------+---------+---------------------------|
| | |This statistic shows the |
| | |number of IPv4 addresses |
| | |that were declined, but |
| | |have now been recovered. |
| | |Unlike declined-addresses, |
| | |this statistic never |
| | |decreases. It can be used |
|subnet[id].reclaimed-declined-addresses| integer |as a long term indicator of|
| | |how many actual valid |
| | |Declines were processed and|
| | |recovered from. The id is |
| | |the subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately. |
+-----------------------------------------------------------------------------+
8.9. Management API for the DHCPv4 Server
The management API allows the issuing of specific management commands,
such as statistics retrieval, reconfiguration or shutdown. For more
details, see Chapter 16, Management API. Currently the only supported
communication channel type is UNIX stream socket. By default there are no
sockets open. To instruct Kea to open a socket, the following entry in the
configuration file can be used:
"Dhcp4": {
"control-socket": {
"socket-type": "unix",
"socket-name": "/path/to/the/unix/socket"
},
"subnet4": [
...
],
...
}
The length of the path specified by the socket-name parameter is
restricted by the maximum length for the unix socket name on your
operating system, i.e. the size of the sun_path field in the sockaddr_un
structure, decreased by 1. This value varies on different operating
systems between 91 and 107 characters. Typical values are 107 on Linux and
103 on FreeBSD.
Communication over control channel is conducted using JSON structures. See
the Control Channel section in the Kea Developer's Guide for more details.
The DHCPv4 server supports the following operational commands:
* build-report
* config-get
* config-reload
* config-set
* config-test
* config-write
* dhcp-disable
* dhcp-enable
* leases-reclaim
* list-commands
* shutdown
* version-get
as described in Section 16.3, "Commands Supported by Both the DHCPv4 and
DHCPv6 Servers". In addition, it supports the following statistics related
commands:
* statistic-get
* statistic-reset
* statistic-remove
* statistic-get-all
* statistic-reset-all
* statistic-remove-all
as described here Section 15.3, "Commands for Manipulating Statistics".
8.10. Supported DHCP Standards
The following standards are currently supported:
* Dynamic Host Configuration Protocol, RFC 2131: Supported messages are
DHCPDISCOVER (1), DHCPOFFER (2), DHCPREQUEST (3), DHCPRELEASE (7),
DHCPINFORM (8), DHCPACK (5), and DHCPNAK(6).
* DHCP Options and BOOTP Vendor Extensions, RFC 2132: Supported options
are: PAD (0), END(255), Message Type(53), DHCP Server Identifier (54),
Domain Name (15), DNS Servers (6), IP Address Lease Time (51), Subnet
mask (1), and Routers (3).
* DHCP Relay Agent Information Option, RFC 3046: Relay Agent Information
option is supported.
* Vendor-Identifying Vendor Options for Dynamic Host Configuration
Protocol version 4, RFC 3925: Vendor-Identifying Vendor Class and
Vendor-Identifying Vendor-Specific Information options are supported.
* Client Identifier Option in DHCP Server Replies, RFC 6842: Server by
default sends back client-id option. That capability may be disabled.
See Section 8.2.18, "Echoing Client-ID (RFC 6842)" for details.
8.11. User contexts in IPv4
Kea allows loading hook libraries that sometimes could benefit from
additional parameters. If such a parameter is specific to the whole
library, it is typically defined as a parameter for the hook library.
However, sometimes there is a need to specify parameters that are
different for each pool.
User contexts can store arbitrary data as long as it is valid JSON syntax
and its top level element is a map (i.e. the data must be enclosed in
curly brackets). Some hook libraries may expect specific formatting,
though. Please consult specific hook library documentation for details.
User contexts can be specified on either global scope, shared network,
subnet, pool, client class, option data or definition level, and host
reservation. One other useful usage is the ability to store comments or
descriptions.
Let's consider an imaginary case of devices that have color LED lights.
Depending on their location, they should glow red, blue or green. It would
be easy to write a hook library that would send specific values as maybe a
vendor option. However, the server has to have some way to specify that
value for each pool. This need is addressed by user contexts. In essence,
any user data can specified in the user context as long as it is a valid
JSON map. For example, the forementioned case of LED devices could be
configured in the following way:
"Dhcp4": {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ {
"pool": "192.0.2.10 - 192.0.2.20",
// This is pool specific user context
"user-context": { "colour": "red" }
} ],
// This is a subnet specific user context. You can put whatever type
// of information you want as long as it is a valid JSON.
"user-context": {
"comment": "network on the second floor",
"last-modified": "2017-09-04 13:32",
"description": "you can put here anything you like",
"phones": [ "x1234", "x2345" ],
"devices-registered": 42,
"billing": false
}
},
...
],
...
}
It should be noted that Kea will not use that information, but will simply
store and make it available to hook libraries. It is up to the hook
library to extract that information and make use of it. The parser
translates a "comment" entry into a user-context with the entry, this
allows to attach a comment inside the configuration itself.
For more background information, see Section 14.5, "User contexts".
8.12. DHCPv4 Server Limitations
These are the current limitations of the DHCPv4 server software. Most of
them are reflections of the current stage of development and should be
treated as "not implemented yet", rather than actual limitations. However,
some of them are implications of the design choices made. Those are
clearly marked as such.
* BOOTP (RFC 951) is not supported. This is a design choice: BOOTP
support is not planned.
* On Linux and BSD system families the DHCP messages are sent and
received over the raw sockets (using LPF and BPF) and all packet
headers (including data link layer, IP and UDP headers) are created
and parsed by Kea, rather than the system kernel. Currently, Kea can
only parse the data link layer headers with a format adhering to IEEE
802.3 standard and assumes this data link layer header format for all
interfaces. Hence, Kea will fail to work on interfaces which use
different data link layer header formats (e.g. Infiniband).
* The DHCPv4 server does not verify that assigned address is unused.
According to RFC 2131, the allocating server should verify that
address is not used by sending ICMP echo request.
8.13. Kea DHCPv4 server examples
A collection of simple to use examples for DHCPv4 component of Kea is
available with the sources. It is located in doc/examples/kea4 directory.
At the time of writing this text there were 15 examples, but the number is
growing slowly with each release.
Chapter 9. The DHCPv6 Server
Table of Contents
9.1. Starting and Stopping the DHCPv6 Server
9.2. DHCPv6 Server Configuration
9.2.1. Introduction
9.2.2. Lease Storage
9.2.3. Hosts Storage
9.2.4. Interface Selection
9.2.5. IPv6 Subnet Identifier
9.2.6. Unicast Traffic Support
9.2.7. Subnet and Address Pool
9.2.8. Subnet and Prefix Delegation Pools
9.2.9. Prefix Exclude Option
9.2.10. Standard DHCPv6 Options
9.2.11. Common Softwire46 Options
9.2.12. Custom DHCPv6 Options
9.2.13. DHCPv6 Vendor-Specific Options
9.2.14. Nested DHCPv6 Options (Custom Option Spaces)
9.2.15. Unspecified Parameters for DHCPv6 Option
Configuration
9.2.16. IPv6 Subnet Selection
9.2.17. Rapid Commit
9.2.18. DHCPv6 Relays
9.2.19. Relay-Supplied Options
9.2.20. Client Classification in DHCPv6
9.2.21. DDNS for DHCPv6
9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side
9.3. Host Reservation in DHCPv6
9.3.1. Address/Prefix Reservation Types
9.3.2. Conflicts in DHCPv6 Reservations
9.3.3. Reserving a Hostname
9.3.4. Including Specific DHCPv6 Options in Reservations
9.3.5. Reserving Client Classes in DHCPv6
9.3.6. Storing Host Reservations in MySQL, PostgreSQL or
Cassandra
9.3.7. Fine Tuning DHCPv6 Host Reservation
9.4. Shared networks in DHCPv6
9.4.1. Local and relayed traffic in shared networks
9.4.2. Client classification in shared networks
9.4.3. Host reservations in shared networks
9.5. Server Identifier in DHCPv6
9.6. Stateless DHCPv6 (Information-Request Message)
9.7. Support for RFC 7550
9.8. Using Specific Relay Agent for a Subnet
9.9. Segregating IPv6 Clients in a Cable Network
9.10. MAC/Hardware Addresses in DHCPv6
9.11. Duplicate Addresses (DECLINE Support)
9.12. Statistics in the DHCPv6 Server
9.13. Management API for the DHCPv6 Server
9.14. User contexts in IPv6
9.15. Supported DHCPv6 Standards
9.16. DHCPv6 Server Limitations
9.17. Kea DHCPv6 server examples
9.1. Starting and Stopping the DHCPv6 Server
It is recommended that the Kea DHCPv6 server be started and stopped using
keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
is also possible to run the server directly: it accepts the following
command-line switches:
* -c file - specifies the configuration file. This is the only mandatory
switch.
* -d - specifies whether the server logging should be switched to
verbose mode. In verbose mode, the logging severity and debuglevel
specified in the configuration file are ignored and "debug" severity
and the maximum debuglevel (99) are assumed. The flag is convenient,
for temporarily switching the server into maximum verbosity, e.g. when
debugging.
* -p port - specifies UDP port on which the server will listen. This is
only useful during testing, as a DHCPv6 server listening on ports
other than the standard ones will not be able to handle regular DHCPv6
queries.
* -t file - specifies the configuration file to be tested. Kea-dhcp6
will attempt to load it, and will conduct sanity checks. Note that
certain checks are possible only while running the actual server. The
actual status is reported with exit code (0 = configuration looks ok,
1 = error encountered). Kea will print out log messages to standard
output and error to standard error when testing configuration.
* -v - prints out the Kea version and exits.
* -V - prints out the Kea extended version with additional parameters
and exits. The listing includes the versions of the libraries
dynamically linked to Kea.
* -W - prints out the Kea configuration report and exits. The report is
a copy of the config.report file produced by ./configure: it is
embedded in the executable binary.
The config.report may also be accessed more directly. The following
command may be used to extract this information. The binary path may be
found in the install directory or in the .libs subdirectory in the source
tree. For example kea/src/bin/dhcp6/.libs/kea-dhcp6.
strings path/kea-dhcp6 | sed -n 's/;;;; //p'
On start-up, the server will detect available network interfaces and will
attempt to open UDP sockets on all interfaces mentioned in the
configuration file. Since the DHCPv6 server opens privileged ports, it
requires root access. Make sure you run this daemon as root.
During startup the server will attempt to create a PID file of the form:
localstatedir]/[conf name].kea-dhcp6.pid where:
* localstatedir: The value as passed into the build configure script. It
defaults to "/usr/local/var". Note that this value may be overridden
at run time by setting the environment variable KEA_PIDFILE_DIR. This
is intended primarily for testing purposes.
* conf name: The configuration file name used to start the server, minus
all preceding path and file extension. For example, given a pathname
of "/usr/local/etc/kea/myconf.txt", the portion used would be
"myconf".
If the file already exists and contains the PID of a live process, the
server will issue a DHCP6_ALREADY_RUNNING log message and exit. It is
possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
The server can be stopped using the kill command. When running in a
console, the server can be shut down by pressing ctrl-c. It detects the
key combination and shuts down gracefully.
9.2. DHCPv6 Server Configuration
9.2.1. Introduction
This section explains how to configure the DHCPv6 server using the Kea
configuration backend. (Kea configuration using any other backends is
outside of scope of this document.) Before DHCPv6 is started, its
configuration file has to be created. The basic configuration is as
follows:
{
# DHCPv6 configuration starts on the next line
"Dhcp6": {
# First we set up global values
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"preferred-lifetime": 3000,
# Next we setup the interfaces to be used by the server.
"interfaces-config": {
"interfaces": [ "eth0" ]
},
# And we specify the type of lease database
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/var/kea/dhcp6.leases"
},
# Finally, we list the subnets from which we will be leasing addresses.
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
]
}
]
# DHCPv6 configuration ends with the next line
}
}
The following paragraphs provide a brief overview of the parameters in the
above example together with their format. Subsequent sections of this
chapter go into much greater detail for these and other parameters.
The lines starting with a hash (#) are comments and are ignored by the
server; they do not impact its operation in any way.
The configuration starts in the first line with the initial opening curly
bracket (or brace). Each configuration consists of one or more objects. In
this specific example, we have only one object, called Dhcp6. This is a
simplified configuration, as usually there will be additional objects,
like Logging or DhcpDdns, but we omit them now for clarity. The Dhcp6
configuration starts with the "Dhcp6": { line and ends with the
corresponding closing brace (in the above example, the brace after the
last comment). Everything defined between those lines is considered to be
the Dhcp6 configuration.
In the general case, the order in which those parameters appear does not
matter. There are two caveats here though. The first one is to remember
that the configuration file must be well formed JSON. That means that
parameters for any given scope must be separated by a comma and there must
not be a comma after the last parameter. When reordering a configuration
file, keep in mind that moving a parameter to or from the last position in
a given scope may also require moving the comma. The second caveat is that
it is uncommon -- although legal JSON -- to repeat the same parameter
multiple times. If that happens, the last occurrence of a given parameter
in a given scope is used while all previous instances are ignored. This is
unlikely to cause any confusion as there are no real life reasons to keep
multiple copies of the same parameter in your configuration file.
Moving onto the DHCPv6 configuration elements, the very first few elements
define some global parameters. valid-lifetime defines for how long the
addresses (leases) given out by the server are valid. If nothing changes,
a client that got an address is allowed to use it for 4000 seconds. (Note
that integer numbers are specified as is, without any quotes around them.)
The address will become deprecated in 3000 seconds (clients are allowed to
keep old connections, but can't use this address for creating new
connections). renew-timer and rebind-timer are values that define T1 and
T2 timers that govern when the client will begin the renewal and rebind
procedures.
The interfaces-config map specifies the server configuration concerning
the network interfaces, on which the server should listen to the DHCP
messages. The interfaces parameter specifies a list of network interfaces
on which the server should listen. Lists are opened and closed with square
brackets, with elements separated by commas. Had we wanted to listen on
two interfaces, the interfaces-config would look like this:
"interfaces-config": {
"interfaces": [ "eth0", "eth1" ]
},
The next couple of lines define the lease database, the place where the
server stores its lease information. This particular example tells the
server to use memfile, which is the simplest (and fastest) database
backend. It uses an in-memory database and stores leases on disk in a CSV
file. This is a very simple configuration. Usually the lease database
configuration is more extensive and contains additional parameters. Note
that lease-database is an object and opens up a new scope, using an
opening brace. Its parameters (just one in this example - type) follow.
Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters for the Dhcp6
definition follow, a trailing comma is present.
Finally, we need to define a list of IPv6 subnets. This is the most
important DHCPv6 configuration structure as the server uses that
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
specified with the subnet6 parameter. It is a list, so it starts and ends
with square brackets. Each subnet definition in the list has several
attributes associated with it, so it is a structure and is opened and
closed with braces. At minimum, a subnet definition has to have at least
two parameters: subnet (that defines the whole subnet) and pools (which is
a list of dynamically allocated pools that are governed by the DHCP
server).
The example contains a single subnet. Had more than one been defined,
additional elements in the subnet6 parameter would be specified and
separated by commas. For example, to define two subnets, the following
syntax would be used:
"subnet6": [
{
"pools": [ { "pool": "2001:db8:1::/112" } ],
"subnet": "2001:db8:1::/64"
},
{
"pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
"subnet": "2001:db8:2::/64"
}
]
Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
After all parameters are specified, we have two contexts open: global and
Dhcp6, hence we need two closing curly brackets to close them. In a real
life configuration file there most likely would be additional components
defined such as Logging or DhcpDdns, so the closing brace would be
followed by a comma and another object definition.
9.2.2. Lease Storage
All leases issued by the server are stored in the lease database.
Currently there are four database backends available: memfile (which is
the default backend), MySQL, PostgreSQL and Cassandra.
9.2.2.1. Memfile - Basic Storage for Leases
The server is able to store lease data in different repositories. Larger
deployments may elect to store leases in a database. Section 9.2.2.2,
"Lease Database Configuration" describes this option. In typical smaller
deployments though, the server will store lease information in a CSV file
rather than a database. As well as requiring less administration, an
advantage of using a file for storage is that it eliminates a dependency
on third-party database software.
The configuration of the file backend (Memfile) is controlled through the
Dhcp6/lease-database parameters. The type parameter is mandatory and it
specifies which storage for leases the server should use. The value of
"memfile" indicates that the file should be used as the storage. The
following list gives additional, optional, parameters that can be used to
configure the Memfile backend.
* persist: controls whether the new leases and updates to existing
leases are written to the file. It is strongly recommended that the
value of this parameter is set to true at all times, during the
server's normal operation. Not writing leases to disk will mean that
if a server is restarted (e.g. after a power failure), it will not
know what addresses have been assigned. As a result, it may hand out
addresses to new clients that are already in use. The value of false
is mostly useful for performance testing purposes. The default value
of the persist parameter is true, which enables writing lease updates
to the lease file.
* name: specifies an absolute location of the lease file in which new
leases and lease updates will be recorded. The default value for this
parameter is "[kea-install-dir]/var/kea/kea-leases6.csv" .
* lfc-interval: specifies the interval in seconds, at which the server
will perform a lease file cleanup (LFC). This removes redundant
(historical) information from the lease file and effectively reduces
the lease file size. The cleanup process is described in more detailed
fashion further in this section. The default value of the lfc-interval
is 3600. A value of 0 disables the LFC.
An example configuration of the Memfile backend is presented below:
"Dhcp6": {
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/tmp/kea-leases6.csv",
"lfc-interval": 1800
}
}
This configuration selects the /tmp/kea-leases6.csv as the storage for
lease information and enables persistence (writing lease updates to this
file). It also configures the backend perform the periodic cleanup of the
lease files, executed every 30 minutes.
It is important to know how the lease file contents are organized to
understand why the periodic lease file cleanup is needed. Every time the
server updates a lease or creates a new lease for the client, the new
lease information must be recorded in the lease file. For performance
reasons, the server does not update the existing client's lease in the
file, as it would potentially require rewriting the entire file. Instead,
it simply appends the new lease information to the end of the file: the
previous lease entries for the client are not removed. When the server
loads leases from the lease file, e.g. at the server startup, it assumes
that the latest lease entry for the client is the valid one. The previous
entries are discarded. This means that the server can re-construct the
accurate information about the leases even though there may be many lease
entries for each client. However, storing many entries for each client
results in bloated lease file and impairs the performance of the server's
startup and reconfiguration as it needs to process a larger number of
lease entries.
Lease file cleanup (LFC) removes all previous entries for each client and
leaves only the latest ones. The interval at which the cleanup is
performed is configurable, and it should be selected according to the
frequency of lease renewals initiated by the clients. The more frequent
the renewals, the smaller the value of lfc-interval should be. Note
however, that the LFC takes time and thus it is possible (although
unlikely) that new cleanup is started while the previous cleanup instance
is still running, if the lfc-interval is too short. The server would
recover from this by skipping the new cleanup when it detects that the
previous cleanup is still in progress. But it implies that the actual
cleanups will be triggered more rarely than configured. Moreover,
triggering a new cleanup adds an overhead to the server which will not be
able to respond to new requests for a short period of time when the new
cleanup process is spawned. Therefore, it is recommended that the
lfc-interval value is selected in a way that would allow for the LFC to
complete the cleanup before a new cleanup is triggered.
Lease file cleanup is performed by a separate process (in background) to
avoid a performance impact on the server process. In order to avoid the
conflicts between two processes both using the same lease files, the LFC
process operates on the copy of the original lease file, rather than on
the lease file used by the server to record lease updates. There are also
other files being created as a side effect of the lease file cleanup. The
detailed description of the LFC is located on the Kea wiki:
http://kea.isc.org/wiki/LFCDesign.
9.2.2.2. Lease Database Configuration
Note
Lease database access information must be configured for the DHCPv6
server, even if it has already been configured for the DHCPv4 server. The
servers store their information independently, so each server can use a
separate database or both servers can use the same database.
Lease database configuration is controlled through the
Dhcp6/lease-database parameters. The type of the database must be set to
"memfile", "mysql", "postgresql" or "cql", e.g.
"Dhcp6": { "lease-database": { "type": "mysql", ... }, ... }
Next, the name of the database is to hold the leases must be set: this is
the name used when the database was created (see Section 4.3.2.1, "First
Time Creation of the MySQL Database", Section 4.3.3.1, "First Time
Creation of the PostgreSQL Database" or Section 4.3.4.1, "First Time
Creation of the Cassandra Database").
"Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... }
For Cassandra:
"Dhcp6": { "lease-database": { "keyspace": "database-name" , ... }, ... }
If the database is located on a different system to the DHCPv6 server, the
database host name must also be specified. (It should be noted that this
configuration may have a severe impact on server performance.):
"Dhcp6": { "lease-database": { "host": "remote-host-name", ... }, ... }
For Cassandra, multiple contact points can be provided:
"Dhcp6": { "lease-database": { "contact-points": "remote-host-name[, ...]" , ... }, ... }
The usual state of affairs will be to have the database on the same
machine as the DHCPv6 server. In this case, set the value to the empty
string:
"Dhcp6": { "lease-database": { "host" : "", ... }, ... }
For Cassandra:
"Dhcp6": { "lease-database": { "contact-points": "", ... }, ... }
Should the database use a port different than default, it may be specified
as well:
"Dhcp6": { "lease-database": { "port" : 12345, ... }, ... }
Should the database be located on a different system, you may need to
specify a longer interval for the connection timeout:
"Dhcp6": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }
The default value of five seconds should be more than adequate for local
connections. If a timeout is given though, it should be an integer greater
than zero.
The maxiumum number of times the server will automatically attempt to
reconnect to the lease database after connectivity has been lost may be
specified:
"Dhcp6": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
If the server is unable to reconnect to the database after making the
maximum number of attempts the server will exit. A value of zero (the
default) disables automatic recovery and the server will exit immediately
upon detecting a loss of connectivity (MySQL and Postgres only).
The number of seconds the server will wait in between attempts to
reconnect to the lease database after connectivity has been lost may also
be specified:
"Dhcp6": { "lease-database": { "reconnect-wait-time" : number-of-seconds, ... }, ... }
A value of zero (the default) disables automatic recovery and the server
will exit immediately upon detecting a loss of connectivity (MySQL and
Postgres only).
Note that host parameter is used by MySQL and PostgreSQL backends.
Cassandra has a concept of contact points that could be used to contact
the cluster, instead of a single IP or hostname. It takes a list of comma
separated IP addresses. This may be specified as:
"Dhcp6": { "lease-database": { "contact-points" : "192.0.2.1,192.0.2.2", ... }, ... }
Finally, the credentials of the account under which the server will access
the database should be set:
"Dhcp6": { "lease-database": { "user": "user-name",
"password": "password",
... },
... }
If there is no password to the account, set the password to the empty
string "". (This is also the default.)
9.2.2.3. Cassandra specific parameters
The parameters are the same for DHCPv4 and DHCPv6. See Section 8.2.2.3,
"Cassandra specific parameters" for details.
9.2.3. Hosts Storage
Kea is also able to store information about host reservations in the
database. The hosts database configuration uses the same syntax as the
lease database. In fact, a Kea server opens independent connections for
each purpose, be it lease or hosts information. This arrangement gives the
most flexibility. Kea can be used to keep leases and host reservations
separately, but can also point to the same database. Currently the
supported hosts database types are MySQL and PostgreSQL. The Cassandra
backend does not support host reservations yet.
Please note that usage of hosts storage is optional. A user can define all
host reservations in the configuration file. That is the recommended way
if the number of reservations is small. However, when the number of
reservations grows it's more convenient to use host storage. Please note
that both storage methods (configuration file and one of the supported
databases) can be used together. If hosts are defined in both places, the
definitions from the configuration file are checked first and external
storage is checked later, if necessary.
Version 1.4 extends the host storage to multiple storages. Operations are
performed on host storages in the configuration order with a special case
for addition: read-only storages must be configured after a required
read-write storage, or host reservation addition will always fail.
9.2.3.1. DHCPv6 Hosts Database Configuration
Hosts database configuration is controlled through the
Dhcp6/hosts-database parameters. If enabled, the type of the database must
be set to "mysql" or "postgresql". Other hosts backends may be added in
later version of Kea.
"Dhcp6": { "hosts-database": { "type": "mysql", ... }, ... }
Next, the name of the database to hold the reservations must be set: this
is the name used when the database was created (see Section 4.3,
"Supported Databases" for instructions how to setup desired database
type).
"Dhcp6": { "hosts-database": { "name": "database-name" , ... }, ... }
If the database is located on a different system than the DHCPv6 server,
the database host name must also be specified. (Again it should be noted
that this configuration may have a severe impact on server performance):
"Dhcp6": { "hosts-database": { "host": remote-host-name, ... }, ... }
The usual state of affairs will be to have the database on the same
machine as the DHCPv6 server. In this case, set the value to the empty
string:
"Dhcp6": { "hosts-database": { "host" : "", ... }, ... }
"Dhcp6": { "hosts-database": { "port" : 12345, ... }, ... }
The maxiumum number of times the server will automatically attempt to
reconnect to the host database after connectivity has been lost may be
specified:
"Dhcp6": { "host-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }
If the server is unable to reconnect to the database after making the
maximum number of attempts the server will exit. A value of zero (the
default) disables automatic recovery and the server will exit immediately
upon detecting a loss of connectivity (MySQL and Postgres only).
The number of seconds the server will wait in between attempts to
reconnect to the host database after connectivity has been lost may also
be specified:
"Dhcp6": { "hosts-database": { "reconnect-wait-time" : number-of-seconds, ... }, ... }
A value of zero (the default) disables automatic recovery and the server
will exit immediately upon detecting a loss of connectivity (MySQL and
Postgres only).
Finally, the credentials of the account under which the server will access
the database should be set:
"Dhcp6": { "hosts-database": { "user": "user-name",
"password": "password",
... },
... }
If there is no password to the account, set the password to the empty
string "". (This is also the default.)
The multiple storage extension uses a similar syntax: a configuration is
placed into a "hosts-databases" list instead of into a "hosts-database"
entry as in:
"Dhcp6": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }
For additional Cassandra specific parameters, see Section 8.2.2.3,
"Cassandra specific parameters".
9.2.3.2. Using Read-Only Databases for Host Reservations
In some deployments the database user whose name is specified in the
database backend configuration may not have write privileges to the
database. This is often required by the policy within a given network to
secure the data from being unintentionally modified. In many cases
administrators have inventory databases deployed, which contain
substantially more information about the hosts than static reservations
assigned to them. The inventory database can be used to create a view of a
Kea hosts database and such view is often read only.
Kea host database backends operate with an implicit configuration to both
read from and write to the database. If the database user does not have
write access to the host database, the backend will fail to start and the
server will refuse to start (or reconfigure). However, if access to a read
only host database is required for retrieving reservations for clients
and/or assign specific addresses and options, it is possible to explicitly
configure Kea to start in "read-only" mode. This is controlled by the
readonly boolean parameter as follows:
"Dhcp6": { "hosts-database": { "readonly": true, ... }, ... }
Setting this parameter to false would configure the database backend to
operate in "read-write" mode, which is also a default configuration if the
parameter is not specified.
Note
The readonly parameter is currently only supported for MySQL and
PostgreSQL databases.
9.2.4. Interface Selection
The DHCPv6 server has to be configured to listen on specific network
interfaces. The simplest network interface configuration instructs the
server to listen on all available interfaces:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "*" ]
}
...
}
The asterisk plays the role of a wildcard and means "listen on all
interfaces". However, it is usually a good idea to explicitly specify
interface names:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ]
},
...
}
It is possible to use wildcard interface name (asterisk) concurrently with
the actual interface names:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3", "*" ]
},
...
}
It is anticipated that this will form of usage only be used where it is
desired to temporarily override a list of interface names and listen on
all interfaces.
As for the DHCPv4 server binding to specific addresses and disabling
re-detection of interfaces are supported. But dhcp-socket-type is not
because DHCPv6 uses UDP/IPv6 sockets only. The following example shows how
to disable the interface detection:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1", "eth3" ],
"re-detect": false
},
...
}
The loopback interfaces (i.e. the "lo" or "lo0" interface) are not
configured by default, unles explicitely mentioned in the configration.
Note Kea requires a link-local address which does not exist on all
systems, or a specified unicast address as in:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "lo/::1" ]
},
...
}
9.2.5. IPv6 Subnet Identifier
The subnet identifier is a unique number associated with a particular
subnet. In principle, it is used to associate clients' leases with their
respective subnets. When a subnet identifier is not specified for a subnet
being configured, it will be automatically assigned by the configuration
mechanism. The identifiers are assigned from 1 and are monotonically
increased for each subsequent subnet: 1, 2, 3 ....
If there are multiple subnets configured with auto-generated identifiers
and one of them is removed, the subnet identifiers may be renumbered. For
example: if there are four subnets and the third is removed the last
subnet will be assigned the identifier that the third subnet had before
removal. As a result, the leases stored in the lease database for subnet 3
are now associated with subnet 4, something that may have unexpected
consequences. It is planned to implement a mechanism to preserve
auto-generated subnet ids in a future version of Kea. However, the only
remedy for this issue at present is to manually specify a unique
identifier for each subnet.
The following configuration will assign the specified subnet identifier to
the newly configured subnet:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"id": 1024,
...
}
]
}
This identifier will not change for this subnet unless the "id" parameter
is removed or set to 0. The value of 0 forces auto-generation of the
subnet identifier.
9.2.6. Unicast Traffic Support
When the DHCPv6 server starts, by default it listens to the DHCP traffic
sent to multicast address ff02::1:2 on each interface that it is
configured to listen on (see Section 9.2.4, "Interface Selection"). In
some cases it is useful to configure a server to handle incoming traffic
sent to the global unicast addresses as well. The most common reason for
this is to have relays send their traffic to the server directly. To
configure the server to listen on a specific unicast address, nn interface
name can be optionally followed by a slash, followed by the global unicast
address on which the server should listen. The server listens to this
address in addition to normal link-local binding and listening on
ff02::1:2 address. The sample configuration below shows how to listen on
2001:db8::1 (a global address) configured on the eth1 interface.
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eth1/2001:db8::1" ]
},
...
"option-data": [
{
"name": "unicast",
"data": "2001:db8::1"
} ],
...
}
This configuration will cause the server to listen on eth1 on the
link-local address, the multicast group (ff02::1:2) and 2001:db8::1.
Usually unicast support is associated with a server unicast option which
allows clients to send unicast messages to the server. The example above
includes a server unicast option specification which will cause the client
to send messages to the specified unicast address.
It is possible to mix interface names, wildcards and interface
name/addresses in the list of interfaces. It is not possible however to
specify more than one unicast address on a given interface.
Care should be taken to specify proper unicast addresses. The server will
attempt to bind to the addresses specified without any additional checks.
This approach has selected on purpose to allow the software to communicate
over uncommon addresses if so desired.
9.2.7. Subnet and Address Pool
The main role of a DHCPv6 server is address assignment. For this, the
server has to be configured with at least one subnet and one pool of
dynamic addresses to be managed. For example, assume that the server is
connected to a network segment that uses the 2001:db8:1::/64 prefix. The
Administrator of that network has decided that addresses from range
2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
server. Such a configuration can be achieved in the following way:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
...
}
]
}
Note that subnet is defined as a simple string, but the pools parameter is
actually a list of pools: for this reason, the pool definition is enclosed
in square brackets, even though only one range of addresses is specified.
Each pool is a structure that contains the parameters that describe a
single pool. Currently there is only one parameter, pool, which gives the
range of addresses in the pool. Additional parameters will be added in
future releases of Kea.
It is possible to define more than one pool in a subnet: continuing the
previous example, further assume that 2001:db8:1:0:5::/80 should also be
managed by the server. It could be written as 2001:db8:1:0:5:: to
2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's is cumbersome. It
can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are
supported by Dhcp6 and can be mixed in the pool list. For example, one
could define the following pools:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" },
{ "pool": "2001:db8:1:05::/80" }
],
...
}
]
}
White space in pool definitions is ignored, so spaces before and after the
hyphen are optional. They can be used to improve readability.
The number of pools is not limited, but for performance reasons it is
recommended to use as few as possible.
The server may be configured to serve more than one subnet. To add a
second subnet, use a command similar to the following:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" }
]
},
{
"subnet": "2001:db8:2::/64",
"pools": [
{ "pool": "2001:db8:2::/64" }
]
},
...
]
}
In this example, we allow the server to dynamically assign all addresses
available in the whole subnet. Although rather wasteful, it is certainly a
valid configuration to dedicate the whole /64 subnet for that purpose.
Note that the Kea server does not preallocate the leases, so there is no
danger in using gigantic address pools.
When configuring a DHCPv6 server using prefix/length notation, please pay
attention to the boundary values. When specifying that the server can use
a given pool, it will also be able to allocate the first (typically
network address) address from that pool. For example, for pool
2001:db8:2::/64 the 2001:db8:2:: address may be assigned as well. If you
want to avoid this, use the "min-max" notation.
9.2.8. Subnet and Prefix Delegation Pools
Subnets may also be configured to delegate prefixes, as defined in RFC
3633. A subnet may have one or more prefix delegation pools. Each pool has
a prefixed address, which is specified as a prefix (prefix) and a prefix
length (prefix-len), as well as a delegated prefix length (delegated-len).
The delegated length must not be shorter (that is it must be numerically
greater or equal) than the prefix length. If both the delegated and prefix
lengths are equal, the server will be able to delegate only one prefix.
The delegated prefix does not have to match the subnet prefix.
Below is a sample subnet configuration which enables prefix delegation for
the subnet:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:d8b:1::/64",
"pd-pools": [
{
"prefix": "3000:1::",
"prefix-len": 64,
"delegated-len": 96
}
]
}
],
...
}
9.2.9. Prefix Exclude Option
For each delegated prefix the delegating router may choose to exclude a
single prefix out of the delegated prefix as specified in the RFC 6603.
The requesting router must not assign the excluded prefix to any of its
downstream interfaces and it is intended to be used on a link through
which the delegating router exchanges DHCPv6 messages with the requesting
router. The configuration example below demonstrates how to specify an
excluded prefix within a prefix pool definition. The excluded prefix
"2001:db8:1:babe:cafe:80::/72" will be sent to a requesting router which
includes Prefix Exclude option in the ORO, and which is delegated a prefix
from this pool.
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pd-pools": [
{
"prefix": "2001:db8:1:8000::",
"prefix-len": 48,
"delegated-len": 64,
"excluded-prefix": "2001:db8:1:babe:cafe:80::",
"excluded-prefix-len": 72
}
]
}
]
}
9.2.10. Standard DHCPv6 Options
One of the major features of a DHCPv6 server is to provide configuration
options to clients. Although there are several options that require
special behavior, most options are sent by the server only if the client
explicitly requests them. The following example shows how to configure DNS
servers, one of the most frequently used options. Options specified in
this way are considered global and apply to all configured subnets.
"Dhcp6": {
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8::cafe, 2001:db8::babe"
},
...
]
}
The option-data line creates a new entry in the option-data table. This
table contains information on all global options that the server is
supposed to configure in all subnets. The name line specifies the option
name. (For a complete list of currently supported names, see Table 9.1,
"List of Standard DHCPv6 Options".) The next line specifies the option
code, which must match one of the values from that list. The line
beginning with space specifies the option space, which must always be set
to "dhcp6" as these are standard DHCPv6 options. For other name spaces,
including custom option spaces, see Section 9.2.14, "Nested DHCPv6 Options
(Custom Option Spaces)". The following line specifies the format in which
the data will be entered: use of CSV (comma separated values) is
recommended. Finally, the data line gives the actual value to be sent to
clients. Data is specified as normal text, with values separated by commas
if more than one value is allowed.
Options can also be configured as hexadecimal values. If "csv-format" is
set to false, the option data must be specified as a string of hexadecimal
numbers. The following commands configure the DNS-SERVERS option for all
subnets with the following addresses: 2001:db8:1::cafe and
2001:db8:1::babe.
"Dhcp6": {
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": false,
"data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
2001 0DB8 0001 0000 0000 0000 0000 BABE"
},
...
]
}
Note
The value for the setting of the "data" element is split across two lines
in this example for clarity: when entering the command, the whole string
should be entered on the same line.
Care should be taken to use proper encoding when using hexadecimal format
as Kea's ability to validate data correctness in hexadecimal is limited.
Most of the parameters in the "option-data" structure are optional and can
be omitted in some circumstances as discussed in the Section 9.2.15,
"Unspecified Parameters for DHCPv6 Option Configuration". Only one of name
or code is required, so you don't need to specify both. Space has a
default value of "dhcp6", so you can skip this as well if you define a
regular (not encapsulated) DHCPv6 option. Finally, csv-format defaults to
true, so it too can be skipped, unless you want to specify the option
value as hexstring. Therefore the above example can be simplified to:
"Dhcp6": {
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe"
},
...
]
}
Defined options are added to response when the client requests them at a
few exceptions which are always added. To enforce the addition of a
particular option set the always-send flag to true as in:
"Dhcp6": {
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe",
"always-send": true
},
...
]
}
The effect is the same as if the client added the option code in the
Option Request Option (or its equivalent for vendor options) so in:
"Dhcp6": {
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe",
"always-send": true
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:1::cafe, 2001:db8:1::babe"
},
...
],
...
},
...
],
...
}
The DNS Servers option is always added to responses (the always-send is
"sticky") but the value is the subnet one when the client is localized in
the subnet.
It is possible to override options on a per-subnet basis. If clients
connected to most of your subnets are expected to get the same values of a
given option, you should use global options: you can then override
specific values for a small number of subnets. On the other hand, if you
use different values in each subnet, it does not make sense to specify
global option values (Dhcp6/option-data), rather you should set only
subnet-specific values (Dhcp6/subnet[X]/option-data[Y]).
The following commands override the global DNS servers option for a
particular subnet, setting a single DNS server with address 2001:db8:1::3.
"Dhcp6": {
"subnet6": [
{
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:1::3"
},
...
],
...
},
...
],
...
}
In some cases it is useful to associate some options with an address or
prefix pool from which a client is assigned a lease. Pool specific option
values override subnet specific and global option values. If the client is
assigned multiple leases from different pools, the server will assign
options from all pools from which the leases have been obtained. However,
if the particular option is specified in multiple pools from which the
client obtains the leases, only one instance of this option will be handed
out to the client. The server's administrator must not try to prioritize
assignment of pool specific options by trying to order pools declarations
in the server configuration. Future Kea releases may change the order in
which options are assigned from the pools without any notice.
The following configuration snippet demonstrates how to specify the DNS
servers option, which will be assigned to a client only if the client
obtains an address from the given pool:
"Dhcp6": {
"subnet6": [
{
"pools": [
{
"pool": "2001:db8:1::100-2001:db8:1::300",
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:1::10"
}
]
}
]
},
...
],
...
}
Options can be specified also in class of host reservation scope. In Kea
1.4 options precedence order is (from most important): host reservation,
pool, subnet, shared network, class, global. In Kea 1.5 order will be
changed to: host reservation, class, pool, subnet, shared network, global
OR it will be fully configurable.
The currently supported standard DHCPv6 options are listed in Table 9.1,
"List of Standard DHCPv6 Options". The "Name" and "Code" are the values
that should be used as a name in the option-data structures. "Type"
designates the format of the data: the meanings of the various types is
given in Table 8.2, "List of standard DHCP option types".
Experimental options (like standard options but with a code which was not
assigned by IANA) are listed in Table 9.2, "List of Experimental DHCPv6
Options".
When a data field is a string, and that string contains the comma (,;
U+002C) character, the comma must be escaped with a reverse solidus
character (\; U+005C). This double escape is required, because both the
routine splitting CSV data into fields and JSON use the same escape
character: a single escape (\,) would make the JSON invalid. For example,
the string "EST5EDT4,M3.2.0/02:00,M11.1.0/02:00" would be represented as:
"Dhcp6": {
"subnet6": [
{
"pools": [
{
"option-data": [
{
"name": "new-posix-timezone",
"data": "EST5EDT4\,M3.2.0/02:00\,M11.1.0/02:00"
}
]
},
...
],
...
},
...
],
...
}
Some options are designated as arrays, which means that more than one
value is allowed in such an option. For example the option dns-servers
allows the specification of more than one IPv6 address, allowing clients
to obtain the addresses of multiple DNS servers.
The Section 9.2.12, "Custom DHCPv6 Options" describes the configuration
syntax to create custom option definitions (formats). It is generally not
allowed to create custom definitions for standard options, even if the
definition being created matches the actual option format defined in the
RFCs. There is an exception from this rule for standard options for which
Kea does not yes provide a definition. In order to use such options, a
server administrator must create a definition as described in
Section 9.2.12, "Custom DHCPv6 Options" in the 'dhcp6' option space. This
definition should match the option format described in the relevant RFC
but the configuration mechanism would allow any option format as it has no
means to validate the format at the moment.
Table 9.1. List of Standard DHCPv6 Options
+------------------------------------------------------------------------+
| Name | Code | Type | Array? |
|--------------------------+------+-----------------------------+--------|
| preference | 7 | uint8 | false |
|--------------------------+------+-----------------------------+--------|
| unicast | 12 | ipv6-address | false |
|--------------------------+------+-----------------------------+--------|
| vendor-opts | 17 | uint32 | false |
|--------------------------+------+-----------------------------+--------|
| sip-server-dns | 21 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| sip-server-addr | 22 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| dns-servers | 23 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| domain-search | 24 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| nis-servers | 27 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| nisp-servers | 28 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| nis-domain-name | 29 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| nisp-domain-name | 30 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| sntp-servers | 31 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| information-refresh-time | 32 | uint32 | false |
|--------------------------+------+-----------------------------+--------|
| bcmcs-server-dns | 33 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| bcmcs-server-addr | 34 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| geoconf-civic | 36 | record (uint8, uint16, hex) | false |
|--------------------------+------+-----------------------------+--------|
| remote-id | 37 | record (uint32, hex) | false |
|--------------------------+------+-----------------------------+--------|
| subscriber-id | 38 | hex | false |
|--------------------------+------+-----------------------------+--------|
| client-fqdn | 39 | record (uint8, fqdn) | false |
|--------------------------+------+-----------------------------+--------|
| pana-agent | 40 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| new-posix-timezone | 41 | string | false |
|--------------------------+------+-----------------------------+--------|
| new-tzdb-timezone | 42 | string | false |
|--------------------------+------+-----------------------------+--------|
| ero | 43 | uint16 | true |
|--------------------------+------+-----------------------------+--------|
| lq-query (1) | 44 | record (uint8, | false |
| | | ipv6-address) | |
|--------------------------+------+-----------------------------+--------|
| client-data (1) | 45 | empty | false |
|--------------------------+------+-----------------------------+--------|
| clt-time (1) | 46 | uint32 | false |
|--------------------------+------+-----------------------------+--------|
| lq-relay-data (1) | 47 | record (ipv6-address, hex) | false |
|--------------------------+------+-----------------------------+--------|
| lq-client-link (1) | 48 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| v6-lost | 51 | fqdn | false |
|--------------------------+------+-----------------------------+--------|
| capwap-ac-v6 | 52 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| relay-id | 53 | hex | false |
|--------------------------+------+-----------------------------+--------|
| v6-access-domain | 57 | fqdn | false |
|--------------------------+------+-----------------------------+--------|
| sip-ua-cs-list | 58 | fqdn | true |
|--------------------------+------+-----------------------------+--------|
| bootfile-url | 59 | string | false |
|--------------------------+------+-----------------------------+--------|
| bootfile-param | 60 | tuple | true |
|--------------------------+------+-----------------------------+--------|
| client-arch-type | 61 | uint16 | true |
|--------------------------+------+-----------------------------+--------|
| nii | 62 | record (uint8, uint8, | false |
| | | uint8) | |
|--------------------------+------+-----------------------------+--------|
| aftr-name | 64 | fqdn | false |
|--------------------------+------+-----------------------------+--------|
| erp-local-domain-name | 65 | fqdn | false |
|--------------------------+------+-----------------------------+--------|
| rsoo | 66 | empty | false |
|--------------------------+------+-----------------------------+--------|
| pd-exclude | 67 | hex | false |
|--------------------------+------+-----------------------------+--------|
| rdnss-selection | 74 | record (ipv6-address, | true |
| | | uint8, fqdn) | |
|--------------------------+------+-----------------------------+--------|
| client-linklayer-addr | 79 | hex | false |
|--------------------------+------+-----------------------------+--------|
| link-address | 80 | ipv6-address | false |
|--------------------------+------+-----------------------------+--------|
| solmax-rt | 82 | uint32 | false |
|--------------------------+------+-----------------------------+--------|
| inf-max-rt | 83 | uint32 | false |
|--------------------------+------+-----------------------------+--------|
| dhcp4o6-server-addr | 88 | ipv6-address | true |
|--------------------------+------+-----------------------------+--------|
| | | record (uint8, uint8, | |
| s46-rule | 89 | uint8, ipv4-address, | false |
| | | ipv6-prefix) | |
|--------------------------+------+-----------------------------+--------|
| s46-br | 90 | ipv6-address | false |
|--------------------------+------+-----------------------------+--------|
| s46-dmr | 91 | ipv6-prefix | false |
|--------------------------+------+-----------------------------+--------|
| s46-v4v6bind | 92 | record (ipv4-address, | false |
| | | ipv6-prefix) | |
|--------------------------+------+-----------------------------+--------|
| s46-portparams | 93 | record(uint8, psid) | false |
|--------------------------+------+-----------------------------+--------|
| s46-cont-mape | 94 | empty | false |
|--------------------------+------+-----------------------------+--------|
| s46-cont-mapt | 95 | empty | false |
|--------------------------+------+-----------------------------+--------|
| s46-cont-lw | 96 | empty | false |
|--------------------------+------+-----------------------------+--------|
| v6-captive-portal | 103 | string | false |
|--------------------------+------+-----------------------------+--------|
| ipv6-address-andsf | 143 | ipv6-address | true |
+------------------------------------------------------------------------+
Options marked with (1) have option definitions, but the logic behind them
is not implemented. That means that technically Kea knows how to parse
them in incoming message or how to send them if configured to do so, but
not what to do with them. Since the related RFCs require certain
processing, the support for those options is non-functional. However, it
may be useful in some limited lab testing, hence the definition formats
are listed here.
Table 9.2. List of Experimental DHCPv6 Options
+----------------------------------------------------------+
| Name | Code | Type | Array? |
|-------------+------+----------------------------+--------|
| public-key | 701 | hex | false |
|-------------+------+----------------------------+--------|
| certificate | 702 | hex | false |
|-------------+------+----------------------------+--------|
| signature | 703 | record (uint8, uint8, hex) | false |
|-------------+------+----------------------------+--------|
| timestamp | 704 | hex | false |
+----------------------------------------------------------+
9.2.11. Common Softwire46 Options
Softwire46 options are involved in IPv4 over IPv6 provisioning by means of
tunneling or translation as specified in the RFC 7598. The following
sections provide configuration examples of these options.
9.2.11.1. Softwire46 Container Options
S46 container options group rules and optional port parameters for a
specified domain. There are three container options specified in the
"dhcp6" (top level) option space: MAP-E Container option, MAP-T Container
option and S46 Lightweight 4over6 Container option. These options only
contain encapsulated options specified below. They do not include any data
fields.
In order to configure the server to send specific container option along
with all encapsulated options, the container option must be included in
the server configuration as shown below:
"Dhcp6": {
...
"option-data": [
{
"name": "s46-cont-mape"
} ],
...
}
This configuration will cause the server to include MAP-E Container option
to the client. Use "s46-cont-mapt" or "s46-cont-lw" for the MAP-T
Container and S46 Lightweight 4over6 Container options respectively.
All remaining softwire options described below are included in one of the
container options. Thus, they have to be included in appropriate option
spaces by selecting a "space" name, which specifies in which option they
are supposed to be included.
9.2.11.2. S46 Rule Option
The S46 Rule option is used for conveying the Basic Mapping Rule (BMR) and
Forwarding Mapping Rule (FMR).
{
"space": "s46-cont-mape-options",
"name": "s46-rule",
"data": "128, 0, 24, 192.0.2.0, 2001:db8:1::/64"
}
Other possible "space" value is "s46-cont-mapt-options".
The S46 Rule option conveys a number of parameters:
* flags, an unsigned 8 bits integer, with currently only the most
significant bit specified. It denotes whether the rule can be used for
forwarding (128) or not (0).
* ea-len, an 8 bits long Embedded Address length. Allowed values range
from 0 to 48.
* IPv4 prefix length, 8 bits long; expresses the prefix length of the
Rule IPv4 prefix specified in the ipv4-prefix field. Allowed values
range from 0 to 32.
* IPv4 prefix, a fixed-length 32-bit field that specifies the IPv4
prefix for the S46 rule. The bits in the prefix after prefix4-len
number of bits are reserved and MUST be initialized to zero by the
sender and ignored by the receiver.
* IPv6 prefix in prefix/length notation that specifies the IPv6 domain
prefix for the S46 rule. The field is padded on the right with zero
bits up to the nearest octet boundary when prefix6-len is not evenly
divisible by 8.
9.2.11.3. S46 BR Option
The S46 BR option is used to convey the IPv6 address of the Border Relay.
This option is mandatory in the MAP-E Container option and not permitted
in the MAP-T and S46 Lightweight 4over6 Container options.
{
"space": "s46-cont-mape-options",
"name": "s46-br",
"data": "2001:db8:cafe::1",
}
Other possible "space" value is "s46-cont-lw-options".
9.2.11.4. S46 DMR Option
The S46 DMR option is used to convey values for the Default Mapping Rule
(DMR). This option is mandatory in the MAP-T container option and not
permitted in the MAP-E and S46 Lightweight 4over6 Container options.
{
"space": "s46-cont-mapt-options",
"name": "s46-dmr",
"data": "2001:db8:cafe::/64",
}
This option must not be included in other containers.
9.2.11.5. S46 IPv4/IPv6 Address Binding option.
The S46 IPv4/IPv6 Address Binding option may be used to specify the full
or shared IPv4 address of the Customer Edge (CE). The IPv6 prefix field is
used by the CE to identify the correct prefix to use for the tunnel
source.
{
"space": "s46-cont-lw",
"name": "s46-v4v6bind",
"data": "192.0.2.3, 2001:db8:1:cafe::/64"
}
This option must not be included in other containers.
9.2.11.6. S46 Port Parameters
The S46 Port Parameters option specifies optional port set information
that MAY be provided to CEs
{
"space": "s46-rule-options",
"name": "s46-portparams",
"data": "2, 3/4",
}
Other possible "space" value is "s46-v4v6bind" to include this option in
the S46 IPv4/IPv6 Address Binding option.
Note that the second value in the example above specifies the PSID and
PSID length fields in the format of PSID/PSID length. This is equivalent
to the values of PSID-len=4 and PSID=12288 conveyed in the S46 Port
Parameters option.
9.2.12. Custom DHCPv6 Options
It is possible to define options in addition to the standard ones. Assume
that we want to define a new DHCPv6 option called "foo" which will have
code 100 and which will convey a single unsigned 32 bit integer value. We
can define such an option by using the following commands:
"Dhcp6": {
"option-def": [
{
"name": "foo",
"code": 100,
"type": "uint32",
"array": false,
"record-types": "",
"space": "dhcp6",
"encapsulate": ""
}, ...
],
...
}
The "false" value of the array parameter determines that the option does
NOT comprise an array of "uint32" values but rather a single value. Two
other parameters have been left blank: record-types and encapsulate. The
former specifies the comma separated list of option data fields if the
option comprises a record of data fields. The record-types value should be
non-empty if the type is set to "record". Otherwise it must be left blank.
The latter parameter specifies the name of the option space being
encapsulated by the particular option. If the particular option does not
encapsulate any option space it should be left blank. Note that the above
example only defines the format of the new option, it does not set its
value(s).
The name, code and type parameters are required, all others are optional.
The array default value is false. The record-types and encapsulate default
values are blank (i.e. ""). The default space is "dhcp6".
Once the new option format is defined, its value is set in the same way as
for a standard option. For example the following commands set a global
value that applies to all subnets.
"Dhcp6": {
"option-data": [
{
"name": "foo",
"code": 100,
"space": "dhcp6",
"csv-format": true,
"data": "12345"
}, ...
],
...
}
New options can take more complex forms than simple use of primitives
(uint8, string, ipv6-address etc): it is possible to define an option
comprising a number of existing primitives.
For example, assume we want to define a new option that will consist of an
IPv6 address, followed by an unsigned 16 bit integer, followed by a
boolean value, followed by a text string. Such an option could be defined
in the following way:
"Dhcp6": {
"option-def": [
{
"name": "bar",
"code": 101,
"space": "dhcp6",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, boolean, string",
"encapsulate": ""
}, ...
],
...
}
The "type" is set to "record" to indicate that the option contains
multiple values of different types. These types are given as a
comma-separated list in the "record-types" field and should be those
listed in Table 8.2, "List of standard DHCP option types".
The values of the option are set as follows:
"Dhcp6": {
"option-data": [
{
"name": "bar",
"space": "dhcp6",
"code": 101,
"csv-format": true,
"data": "2001:db8:1::10, 123, false, Hello World"
}
],
...
}
csv-format is set true to indicate that the data field comprises a
command-separated list of values. The values in the "data" must correspond
to the types set in the "record-types" field of the option definition.
When array is set to true and type is set to "record", the last field is
an array, i.e., it can contain more than one value as in:
"Dhcp6": {
"option-def": [
{
"name": "bar",
"code": 101,
"space": "dhcp6",
"type": "record",
"array": true,
"record-types": "ipv6-address, uint16",
"encapsulate": ""
}, ...
],
...
}
The new option content is one IPv6 address followed by one or more 16 bit
unsigned integers.
Note
In the general case, boolean values are specified as true or false,
without quotes. Some specific boolean parameters may accept also "true",
"false", 0, 1, "0" and "1". Future versions of Kea will accept all those
values for all boolean parameters.
9.2.13. DHCPv6 Vendor-Specific Options
Currently there are two option spaces defined for the DHCPv6 daemon:
"dhcp6" (for top level DHCPv6 options) and "vendor-opts-space", which is
empty by default, but in which options can be defined. Those options will
be carried in the Vendor-Specific Information option (code 17). The
following examples show how to define an option "foo" with code 1 that
consists of an IPv6 address, an unsigned 16 bit integer and a string. The
"foo" option is conveyed in a Vendor-Specific Information option. This
option comprises a single uint32 value that is set to "12345". The
sub-option "foo" follows the data field holding this value.
"Dhcp6": {
"option-def": [
{
"name": "foo",
"code": 1,
"space": "vendor-opts-space",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, string",
"encapsulate": ""
}
],
...
}
(Note that the option space is set to vendor-opts-space.) Once the option
format is defined, the next step is to define actual values for that
option:
"Dhcp6": {
"option-data": [
{
"name": "foo",
"space": "vendor-opts-space",
"data": "2001:db8:1::10, 123, Hello World"
},
...
],
...
}
We should also define a value (enterprise-number) for the Vendor-specific
Information option, that conveys our option "foo".
"Dhcp6": {
"option-data": [
...,
{
"name": "vendor-opts",
"data": "12345"
}
],
...
}
Alternatively, the option can be specified using its code.
"Dhcp6": {
"option-data": [
...,
{
"code": 17,
"data": "12345"
}
],
...
}
9.2.14. Nested DHCPv6 Options (Custom Option Spaces)
It is sometimes useful to define completely new option spaces. This is
useful if the user wants their new option to convey sub-options that use a
separate numbering scheme, for example sub-options with codes 1 and 2.
Those option codes conflict with standard DHCPv6 options, so a separate
option space must be defined.
Note that it is not required to create a new option space when defining
sub-options for a standard option because it is created by default if the
standard option is meant to convey any sub-options (see Section 9.2.13,
"DHCPv6 Vendor-Specific Options").
Assume that we want to have a DHCPv6 option called "container" with code
102 that conveys two sub-options with codes 1 and 2. First we need to
define the new sub-options:
"Dhcp6": {
"option-def": [
{
"name": "subopt1",
"code": 1,
"space": "isc",
"type": "ipv6-address",
"record-types": "",
"array": false,
"encapsulate": ""
},
{
"name": "subopt2",
"code": 2,
"space": "isc",
"type": "string",
"record-types": "",
"array": false
"encapsulate": ""
}
],
...
}
Note that we have defined the options to belong to a new option space (in
this case, "isc").
The next step is to define a regular DHCPv6 option and specify that it
should include options from the isc option space:
"Dhcp6": {
"option-def": [
...,
{
"name": "container",
"code": 102,
"space": "dhcp6",
"type": "empty",
"array": false,
"record-types": "",
"encapsulate": "isc"
}
],
...
}
The name of the option space in which the sub-options are defined is set
in the encapsulate field. The type field is set to empty which limits this
option to only carrying data in sub-options.
Finally, we can set values for the new options:
"Dhcp6": {
"option-data": [
{
"name": "subopt1",
"code": 1,
"space": "isc",
"data": "2001:db8::abcd"
},
}
"name": "subopt2",
"code": 2,
"space": "isc",
"data": "Hello world"
},
{
"name": "container",
"code": 102,
"space": "dhcp6"
}
],
...
}
Note that it is possible to create an option which carries some data in
addition to the sub-options defined in the encapsulated option space. For
example, if the "container" option from the previous example was required
to carry an uint16 value as well as the sub-options, the "type" value
would have to be set to "uint16" in the option definition. (Such an option
would then have the following data structure: DHCP header, uint16 value,
sub-options.) The value specified with the "data" parameter -- which
should be a valid integer enclosed in quotes, e.g. "123" -- would then be
assigned to the uint16 field in the "container" option.
9.2.15. Unspecified Parameters for DHCPv6 Option Configuration
In many cases it is not required to specify all parameters for an option
configuration and the default values can be used. However, it is important
to understand the implications of not specifying some of them as it may
result in configuration errors. The list below explains the behavior of
the server when a particular parameter is not explicitly specified:
* name - the server requires an option name or option code to identify
an option. If this parameter is unspecified, the option code must be
specified.
* code - the server requires an option name or option code to identify
an option. This parameter may be left unspecified if the name
parameter is specified. However, this also requires that the
particular option has its definition (it is either a standard option
or an administrator created a definition for the option using an
'option-def' structure), as the option definition associates an option
with a particular name. It is possible to configure an option for
which there is no definition (unspecified option format).
Configuration of such options requires the use of option code.
* space - if the option space is unspecified it will default to 'dhcp6'
which is an option space holding DHCPv6 standard options.
* data - if the option data is unspecified it defaults to an empty
value. The empty value is mostly used for the options which have no
payload (boolean options), but it is legal to specify empty values for
some options which carry variable length data and which spec allows
for the length of 0. For such options, the data parameter may be
omitted in the configuration.
* csv-format - if this value is not specified the server will assume
that the option data is specified as a list of comma separated values
to be assigned to individual fields of the DHCP option. This behavior
has changed in Kea 1.2. Older versions used additional logic to
determine whether the csv-format should be true or false. That is no
longer the case.
9.2.16. IPv6 Subnet Selection
The DHCPv6 server may receive requests from local (connected to the same
subnet as the server) and remote (connecting via relays) clients. As the
server may have many subnet configurations defined, it must select an
appropriate subnet for a given request.
The server can not assume which of the configured subnets are local. In
IPv4 it is possible as there is a reasonable expectation that the server
will have a (global) IPv4 address configured on the interface, and can use
that information to detect whether a subnet is local or not. That
assumption is not true in IPv6: the DHCPv6 server must be able to operate
while only using link-local addresses. Therefore an optional interface
parameter is available within a subnet definition to designate that a
given subnet is local, i.e. reachable directly over the specified
interface. For example the server that is intended to serve a local subnet
over eth0 may be configured as follows:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
"interface": "eth0"
}
],
...
}
9.2.17. Rapid Commit
The Rapid Commit option, described in RFC 3315, is supported by the Kea
DHCPv6 server. However, support is disabled by default for all subnets. It
can be enabled for a particular subnet using the rapid-commit parameter as
shown below:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"rapid-commit": true,
"pools": [
{
"pool": "2001:db8:beef::1-2001:db8:beef::10"
}
],
}
],
...
}
This setting only affects the subnet for which the rapid-commit is set to
true. For clients connected to other subnets, the server will ignore the
Rapid Commit option sent by the client and will follow the 4-way exchange
procedure, i.e. respond with an Advertise for a Solicit containing a Rapid
Commit option.
9.2.18. DHCPv6 Relays
A DHCPv6 server with multiple subnets defined must select the appropriate
subnet when it receives a request from a client. For clients connected via
relays, two mechanisms are used:
The first uses the linkaddr field in the RELAY_FORW message. The name of
this field is somewhat misleading in that it does not contain a link-layer
address: instead, it holds an address (typically a global address) that is
used to identify a link. The DHCPv6 server checks if the address belongs
to a defined subnet and, if it does, that subnet is selected for the
client's request.
The second mechanism is based on interface-id options. While forwarding a
client's message, relays may insert an interface-id option into the
message that identifies the interface on the relay that received the
message. (Some relays allow configuration of that parameter, but it is
sometimes hardcoded and may range from the very simple (e.g. "vlan100") to
the very cryptic: one example seen on real hardware was
"ISAM144|299|ipv6|nt:vp:1:110"). The server can use this information to
select the appropriate subnet. The information is also returned to the
relay which then knows the interface to use to transmit the response to
the client. In order for this to work successfully, the relay interface
IDs must be unique within the network and the server configuration must
match those values.
When configuring the DHCPv6 server, it should be noted that two
similarly-named parameters can be configured for a subnet:
* interface defines which local network interface can be used to access
a given subnet.
* interface-id specifies the content of the interface-id option used by
relays to identify the interface on the relay to which the response
packet is sent.
The two are mutually exclusive: a subnet cannot be both reachable locally
(direct traffic) and via relays (remote traffic). Specifying both is a
configuration error and the DHCPv6 server will refuse such a
configuration.
The following example configuration shows how to specify an interface-id
with a value of "vlan123".
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
"interface-id": "vlan123"
}
],
...
}
9.2.19. Relay-Supplied Options
RFC 6422 defines a mechanism called Relay-Supplied DHCP Options. In
certain cases relay agents are the only entities that may have specific
information. They can insert options when relaying messages from the
client to the server. The server will then do certain checks and copy
those options to the response that will be sent to the client.
There are certain conditions that must be met for the option to be
included. First, the server must not provide the option itself. In other
words, if both relay and server provide an option, the server always takes
precedence. Second, the option must be RSOO-enabled. IANA maintains a list
of RSOO-enabled options here. However, there may be cases when system
administrators want to echo other options. Kea can be instructed to treat
other options as RSOO-enabled. For example, to mark options 110, 120 and
130 as RSOO-enabled, the following syntax should be used:
"Dhcp6": {
"relay-supplied-options": [ "110", "120", "130" ],
...
}
As of March 2015, only option 65 is RSOO-enabled by IANA. This option will
always be treated as such and there's no need to explicitly mark it. Also,
when enabling standard options, it is possible to use their names, rather
than option code, e.g. (e.g. use dns-servers instead of 23). See
Table 9.1, "List of Standard DHCPv6 Options" for the names. In certain
cases it could also work for custom options, but due to the nature of the
parser code this may be unreliable and should be avoided.
9.2.20. Client Classification in DHCPv6
The DHCPv6 server includes support for client classification. For a deeper
discussion of the classification process see Chapter 13, Client
Classification.
In certain cases it is useful to configure the server to differentiate
between DHCP clients types and treat them accordingly. It is envisaged
that client classification will be used for modifying the behavior of
almost any part of the DHCP message processing. In the current release of
Kea, there are three mechanisms that take advantage of the client
classification in DHCPv6: subnet selection, address pool selection and
DHCP options assignment.
In certain cases it is useful to differentiate between different types of
clients and treat them accordingly. It is envisaged that client
classification will be used for changing the behavior of almost any part
of the DHCP message processing. In the current release of the software
however, there are only some mechanisms that take advantage of client
classification: subnet selection, pool selection, and assignment of
different options.
Kea can be instructed to limit access to given subnets based on class
information. This is particularly useful for cases where two types of
devices share the same link and are expected to be served from two
different subnets. The primary use case for such a scenario is cable
networks. Here, there are two classes of devices: the cable modem itself,
which should be handed a lease from subnet A and all other devices behind
the modem that should get a lease from subnet B. That segregation is
essential to prevent overly curious users from playing with their cable
modems. For details on how to set up class restrictions on subnets, see
Section 13.6, "Configuring Subnets With Class Information".
When subnets belong to a shared network the classification applies to
subnet selection but not to pools, e.g., a pool in a subnet limited to a
particular class can still be used by clients which do not belong to the
class if the pool they are expected to use is exhausted. So the limit
access based on class information is also available at the address/prefix
pool level, see Section 13.7, "Configuring Pools With Class Information"
within a subnet. This is useful when to segregate clients belonging to the
same subnet into different address ranges.
In a similar way a pool can be constrained to serve only known clients,
i.e. clients which have a reservation, using the built-in "KNOWN" or
"UNKNOWN" classes. One can assign addresses to registered clients without
giving a different address per reservations, for instance when there is
not enough available addresses. The determination whether there is a
reservation for a given client is made after a subnet is selected. As
such, it is not possible to use KNOWN/UNKNOWN classes to select a shared
network or a subnet.
The process of doing classification is conducted in five steps. The first
step is to assess an incoming packet and assign it to zero or more
classes. The second step is to choose a subnet, possibly based on the
class information. The next step is to evaluate class expressions
depending on the built-in "KNOWN"/"UNKNOWN" classes after host reservation
lookup, using them for pool/pd-pool selection and to assign classes from
host reservations. After the list of required classes is built and each
class of the list has its expression evaluated: when it returns true the
packet is added as a member of the class. The last step is to assign
options again possibly based on the class information. More complete and
detailed description is available in Chapter 13, Client Classification.
There are two main methods of doing classification. The first is automatic
and relies on examining the values in the vendor class options or
existence of a host reservation. Information from these options is
extracted and a class name is constructed from it and added to the class
list for the packet. The second allows for specifying an expression that
is evaluated for each packet. If the result is true the packet is a member
of the class.
Note
Care should be taken with client classification as it is easy for clients
that do not meet class criteria to be denied any service altogether.
9.2.20.1. Defining and Using Custom Classes
The following example shows how to configure a class using an expression
and a subnet making use of that class. This configuration defines the
class named "Client_enterprise". It is comprised of all clients whose
client identifiers start with the given hex string (which would indicate a
DUID based on an enterprise id of 0xAABBCCDD). They will be given an
address from 2001:db8:1::0 to 2001:db8:1::FFFF and the addresses of their
DNS servers set to 2001:db8:0::1 and 2001:db8:2::1.
"Dhcp6": {
"client-classes": [
{
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
"client-class": "Client_enterprise"
}
],
...
}
This example shows a configuration using an automatically generated
"VENDOR_CLASS_" class. The Administrator of the network has decided that
addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are going to be
managed by the Dhcp6 server and only clients belonging to the eRouter1.0
client class are allowed to use that pool.
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff"
}
],
"client-class": "VENDOR_CLASS_eRouter1.0"
}
],
...
}
9.2.20.2. Required classification
In some cases it is useful to limit the scope of a class to a
shared-network, subnet or pool. There are two parameters which are used to
limit the scope of the class by instructing the server to perform
evaluation of test expressions when required.
The first one is the per-class only-if-required flag which is false by
default. When it is set to true the test expression of the class is not
evaluated at the reception of the incoming packet but later and only if
the class evaluation is required.
The second is the require-client-classes which takes a list of class names
and is valid in shared-network, subnet and pool scope. Classes in these
lists are marked as required and evaluated after selection of this
specific shared-network/subnet/pool and before output option processing.
In this example, a class is assigned to the incoming packet when the
specified subnet is used.
"Dhcp6": {
"client-classes": [
{
"name": "Client_foo",
"test": "member('ALL')",
"only-if-required": true
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64"
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff"
}
],
"require-client-classes": [ "Client_foo" ],
...
},
...
],
...
}
Required evaluation can be used to express complex dependencies, for
example, subnet membership. It can also be used to reverse the precedence:
if you set an option-data in a subnet it takes precedence over an
option-data in a class. When you move the option-data to a required class
and require it in the subnet, a class evaluated earlier may take
precedence.
Required evaluation is also available at shared-network and pool/pd-pool
levels. The order in which required classes are considered is:
shared-network, subnet and (pd-)pool, i.e. the opposite order option-data
are processed.
9.2.21. DDNS for DHCPv6
As mentioned earlier, kea-dhcp6 can be configured to generate requests to
the DHCP-DDNS server (referred to here as "D2") to update DNS entries.
These requests are known as NameChangeRequests or NCRs. Each NCR contains
the following information:
1. Whether it is a request to add (update) or remove DNS entries
2. Whether the change requests forward DNS updates (AAAA records),
reverse DNS updates (PTR records), or both.
3. The FQDN, lease address, and DHCID
The parameters controlling the generation of NCRs for submission to D2 are
contained in the dhcp-ddns section of the kea-dhcp6 configuration. The
mandatory parameters for the DHCP DDNS configuration are enable-updates
which is unconditionally required, and qualifying-suffix which has no
default value and is required when enable-updates is set to true. The two
(disabled and enabled) minimal DHCP DDNS configurations are:
"Dhcp6": {
"dhcp-ddns": {
"enable-updates": false
},
...
}
and for example:
"Dhcp6": {
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example."
},
...
}
The default values for the "dhcp-ddns" section are as follows:
* "server-ip": "127.0.0.1"
* "server-port": 53001
* "sender-ip": ""
* "sender-port": 0
* "max-queue-size": 1024
* "ncr-protocol": "UDP"
* "ncr-format": "JSON"
* "override-no-update": false
* "override-client-update": false
* "replace-client-name": "never"
* "generated-prefix": "myhost"
9.2.21.1. DHCP-DDNS Server Connectivity
In order for NCRs to reach the D2 server, kea-dhcp6 must be able to
communicate with it. kea-dhcp6 uses the following configuration parameters
to control this communication:
* enable-updates - determines whether or not kea-dhcp6 will generate
NCRs. If missing, this value is assumed to be false hence DDNS updates
are disabled. To enable DDNS updates set this value to true:
* server-ip - IP address on which D2 listens for requests. The default
is the local loopback interface at address 127.0.0.1. You may specify
either an IPv4 or IPv6 address.
* server-port - port on which D2 listens for requests. The default value
is 53001.
* sender-ip - IP address which kea-dhcp6 should use to send requests to
D2. The default value is blank which instructs kea-dhcp6 to select a
suitable address.
* sender-port - port which kea-dhcp6 should use to send requests to D2.
The default value of 0 instructs kea-dhcp6 to select a suitable port.
* max-queue-size - maximum number of requests allowed to queue waiting
to be sent to D2. This value guards against requests accumulating
uncontrollably if they are being generated faster than they can be
delivered. If the number of requests queued for transmission reaches
this value, DDNS updating will be turned off until the queue backlog
has been sufficiently reduced. The intent is to allow kea-dhcp6 to
continue lease operations. The default value is 1024.
* ncr-protocol - socket protocol use when sending requests to D2.
Currently only UDP is supported. TCP may be available in an upcoming
release.
* ncr-format - packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be
available in future releases.
By default, kea-dhcp-ddns is assumed to running on the same machine as
kea-dhcp6, and all of the default values mentioned above should be
sufficient. If, however, D2 has been configured to listen on a different
address or port, these values must altered accordingly. For example, if D2
has been configured to listen on 2001:db8::5 port 900, the following
configuration would be required:
"Dhcp6": {
"dhcp-ddns": {
"server-ip": "2001:db8::5",
"server-port": 900,
...
},
...
}
9.2.21.2. When Does kea-dhcp6 Generate a DDNS Request?
kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704. It
is important to keep in mind that kea-dhcp6 provides the initial decision
making of when and what to update and forwards that information to D2 in
the form of NCRs. Carrying out the actual DNS updates and dealing with
such things as conflict resolution are within the purview of D2 itself
(Chapter 11, The DHCP-DDNS Server). This section describes when kea-dhcp6
will generate NCRs and the configuration parameters that can be used to
influence this decision. It assumes that the enable-updates parameter is
true.
Note
Currently the interface between kea-dhcp6 and D2 only supports requests
which update DNS entries for a single IP address. If a lease grants more
than one address, kea-dhcp6 will create the DDNS update request for only
the first of these addresses. Support for multiple address mappings may be
provided in a future release.
In general, kea-dhcp6 will generate DDNS update requests when:
1. A new lease is granted in response to a REQUEST
2. An existing lease is renewed but the FQDN associated with it has
changed.
3. An existing lease is released in response to a RELEASE
In the second case, lease renewal, two DDNS requests will be issued: one
request to remove entries for the previous FQDN and a second request to
add entries for the new FQDN. In the last case, a lease release, a single
DDNS request to remove its entries will be made.
The decision making involved when granting a new lease the first case) is
more involved. When a new lease is granted, kea-dhcp6 will generate a DDNS
update request only if the REQUEST contains the FQDN option (code 39). By
default kea-dhcp6 will respect the FQDN N and S flags specified by the
client as shown in the following table:
Table 9.3. Default FQDN Flag Behavior
+------------------------------------------------------------------------+
| Client | Client Intent | Server Response | Server |
| Flags:N-S | | | Flags:N-S-O |
|-----------+-------------------------+--------------------+-------------|
| | Client wants to do | Server generates | |
| 0-0 | forward updates, server | reverse-only | 1-0-0 |
| | should do reverse | request | |
| | updates | | |
|-----------+-------------------------+--------------------+-------------|
| | Server should do both | Server generates | |
| 0-1 | forward and reverse | request to update | 0-1-0 |
| | updates | both directions | |
|-----------+-------------------------+--------------------+-------------|
| 1-0 | Client wants no updates | Server does not | 1-0-0 |
| | done | generate a request | |
+------------------------------------------------------------------------+
The first row in the table above represents "client delegation". Here the
DHCP client states that it intends to do the forward DNS updates and the
server should do the reverse updates. By default, kea-dhcp6 will honor the
client's wishes and generate a DDNS request to D2 to update only reverse
DNS data. The parameter, override-client-update, can be used to instruct
the server to override client delegation requests. When this parameter is
true, kea-dhcp6 will disregard requests for client delegation and generate
a DDNS request to update both forward and reverse DNS data. In this case,
the N-S-O flags in the server's response to the client will be 0-1-1
respectively.
(Note that the flag combination N=1, S=1 is prohibited according to RFC
4702. If such a combination is received from the client, the packet will
be dropped by kea-dhcp6.)
To override client delegation, set the following values in the
configuration:
"Dhcp6": {
"dhcp-ddns": {
"override-client-update": true,
...
},
...
}
The third row in the table above describes the case in which the client
requests that no DNS updates be done. The parameter, override-no-update,
can be used to instruct the server to disregard the client's wishes. When
this parameter is true, kea-dhcp6 will generate DDNS update requests to
kea-dhcp-ddns even if the client requests no updates be done. The N-S-O
flags in the server's response to the client will be 0-1-1.
To override client delegation, issue the following commands:
"Dhcp6": {
"dhcp-ddns": {
"override-no-update": true,
...
},
...
}
9.2.21.3. kea-dhcp6 Name Generation for DDNS Update Requests
Each NameChangeRequest must of course include the fully qualified domain
name whose DNS entries are to be affected. kea-dhcp6 can be configured to
supply a portion or all of that name based upon what it receives from the
client.
The default rules for constructing the FQDN that will be used for DNS
entries are:
1. If the DHCPREQUEST contains the client FQDN option, the candidate name
is taken from there.
2. If the candidate name is a partial (i.e. unqualified) name then add a
configurable suffix to the name and use the result as the FQDN.
3. If the candidate name provided is empty, generate an FQDN using a
configurable prefix and suffix.
4. If the client provided neither option, then no DNS action will be
taken.
These rules can amended by setting the replace-client-name parameter which
provides the following modes of behavior:
* never - Use the name the client sent. If the client sent no name, do
not generate one. This is the default mode.
* always - Replace the name the client sent. If the client sent no name,
generate one for the client.
* when-present - Replace the name the client sent. If the client sent no
name, do not generate one.
* when-not-present - Use the name the client sent. If the client sent no
name, generate one for the client.
Note
Note that formerly, this parameter was a boolean and permitted only values
of true and false. Boolean values have been deprecated and are no longer
accepted. If you are currently using booleans, you must replace them with
the desired mode name. A value of true maps to "when-present", while false
maps to "never".
For example, To instruct kea-dhcp6 to always generate the FQDN for a
client, set the parameter replace-client-name to always as follows:
"Dhcp6": {
"dhcp-ddns": {
"replace-client-name": "always",
...
},
...
}
The prefix used in the generation of an FQDN is specified by the
generated-prefix parameter. The default value is "myhost". To alter its
value, simply set it to the desired string:
"Dhcp6": {
"dhcp-ddns": {
"generated-prefix": "another.host",
...
},
...
}
The suffix used when generating an FQDN or when qualifying a partial name
is specified by the qualifying-suffix parameter. This parameter has no
default value, thus it is mandatory when DDNS updates are enabled. To set
its value simply set it to the desired string:
"Dhcp6": {
"dhcp-ddns": {
"qualifying-suffix": "foo.example.org",
...
},
...
}
When qualifying a partial name, kea-dhcp6 will construct a name with the
format:
[candidate-name].[qualifying-suffix].
where candidate-name is the partial name supplied in the REQUEST. For
example, if FQDN domain name value was "some-computer" and
qualifying-suffix "example.com", the generated FQDN would be:
some-computer.example.com.
When generating the entire name, kea-dhcp6 will construct name of the
format:
[generated-prefix]-[address-text].[qualifying-suffix].
where address-text is simply the lease IP address converted to a
hyphenated string. For example, if lease address is 3001:1::70E, the
qualifying suffix "example.com", and the default value is used for
generated-prefix, the generated FQDN would be:
myhost-3001-1--70E.example.com.
9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side
The support of DHCPv4-over-DHCPv6 transport is described in RFC 7341 and
is implemented using cooperating DHCPv4 and DHCPv6 servers. This section
is about the configuration of the DHCPv6 side (the DHCPv4 side is
described in Section 8.2.20, "DHCPv4-over-DHCPv6: DHCPv4 Side").
Note
DHCPv4-over-DHCPv6 support is experimental and the details of the
inter-process communication can change: both the DHCPv4 and DHCPv6 sides
should be running the same version of Kea. For instance the support of
port relay (RFC 8357) introduced such such incompatible change.
There is only one specific parameter for the DHCPv6 side: dhcp4o6-port
which specifies the first of the two consecutive ports of the UDP sockets
used for the communication between the DHCPv6 and DHCPv4 servers (the
DHCPv6 server is bound to ::1 on port and connected to ::1 on port + 1).
Two other configuration entries are in general required: unicast traffic
support (see Section 9.2.6, "Unicast Traffic Support") and DHCP 4o6 server
address option (name "dhcp4o6-server-addr", code 88).
The following configuration was used during some tests:
{
# DHCPv6 conf
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eno33554984/2001:db8:1:1::1" ]
},
"lease-database": {
"type": "memfile",
"name": "leases6"
},
"preferred-lifetime": 3000,
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet6": [ {
"subnet": "2001:db8:1:1::/64",
"interface": "eno33554984",
"pools": [ { "pool": "2001:db8:1:1::1:0/112" } ]
} ],
"dhcp4o6-port": 6767,
"option-data": [ {
"name": "dhcp4o6-server-addr",
"code": 88,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:1:1::1"
} ]
},
"Logging": {
"loggers": [ {
"name": "kea-dhcp6",
"output_options": [ {
"output": "/tmp/kea-dhcp6.log"
} ],
"severity": "DEBUG",
"debuglevel": 0
} ]
}
}
Note
Relayed DHCPv4-QUERY DHCPv6 messages are not yet supported.
9.3. Host Reservation in DHCPv6
There are many cases where it is useful to provide a configuration on a
per host basis. The most obvious one is to reserve specific, static IPv6
address or/and prefix for exclusive use by a given client (host) -
returning client will get the same address or/and prefix every time and
other clients will never get that address. Note that there may be cases
when the new reservation has been made for the client for the address or
prefix being currently in use by another client. We call this situation a
"conflict". The conflicts get resolved automatically over time as
described in the subsequent sections. Once conflict is resolved, the
client will keep receiving the reserved configuration when it renews.
Another example when the host reservations are applicable is when a host
has specific requirements, e.g. a printer that needs additional DHCP
options or a cable modem needs specific parameters. Yet another possible
use case for host reservation is to define unique names for hosts.
Hosts reservations are defined as parameters for each subnet. Each host
can be identified by either DUID or its hardware/MAC address. See
Section 9.10, "MAC/Hardware Addresses in DHCPv6" for details. There is an
optional reservations array in the subnet6 structure. Each element in that
array is a structure, that holds information about a single host. In
particular, the structure has an identifier that uniquely identifies a
host. In the DHCPv6 context, such an identifier is usually a DUID, but can
also be a hardware or MAC address. Also, either one or more addresses or
prefixes may be specified. It is possible to specify a hostname and DHCPv6
options for a given host.
The following example shows how to reserve addresses and prefixes for
specific hosts:
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"pd-pools": [
{
"prefix": "2001:db8:1:8000::",
"prefix-len": 48,
"delegated-len": 64
}
],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
},
{
"hw-address": "00:01:02:03:04:05",
"ip-addresses": [ "2001:db8:1::101", "2001:db8:1::102" ]
},
{
"duid": "01:02:03:04:05:06:07:08:09:0A",
"ip-addresses": [ "2001:db8:1::103" ],
"prefixes": [ "2001:db8:2:abcd::/64" ],
"hostname": "foo.example.com"
}
]
}
]
This example includes reservations for three different clients. The first
reservation is made for the address 2001:db8:1::100 for a client using
DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second reservation is made for two
addresses 2001:db8:1::101 and 2001:db8:1::102 for a client using MAC
address 00:01:02:03:04:05. Lastly, address 2001:db8:1::103 and prefix
2001:db8:2:abcd::/64 are reserved for a client using DUID
01:02:03:04:05:06:07:08:09:0A. The last reservation also assigns a
hostname to this client.
Note that DHCPv6 allows for a single client to lease multiple addresses
and multiple prefixes at the same time. Therefore ip-addresses and
prefixes are plural and are actually arrays. When the client sends
multiple IA options (IA_NA or IA_PD), each reserved address or prefix is
assigned to an individual IA of the appropriate type. If the number of IAs
of specific type is lower than the number of reservations of that type,
the number of reserved addresses or prefixes assigned to the client is
equal to the number of IA_NAs or IA_PDs sent by the client, i.e. some
reserved addresses or prefixes are not assigned. However, they still
remain reserved for this client and the server will not assign them to any
other client. If the number of IAs of specific type sent by the client is
greater than the number of reserved addresses or prefixes, the server will
try to assign all reserved addresses or prefixes to the individual IAs and
dynamically allocate addresses or prefixes to remaining IAs. If the server
cannot assign a reserved address or prefix because it is in use, the
server will select the next reserved address or prefix and try to assign
it to the client. If the server subsequently finds that there are no more
reservations that can be assigned to the client at the moment, the server
will try to assign leases dynamically.
Making a reservation for a mobile host that may visit multiple subnets
requires a separate host definition in each subnet it is expected to
visit. It is not allowed to define multiple host definitions with the same
hardware address in a single subnet. Multiple host definitions with the
same hardware address are valid if each is in a different subnet. The
reservation for a given host should include only one identifier, either
DUID or hardware address. Defining both for the same host is considered a
configuration error, but as of 1.1.0, it is not rejected.
Adding host reservation incurs a performance penalty. In principle, when a
server that does not support host reservation responds to a query, it
needs to check whether there is a lease for a given address being
considered for allocation or renewal. The server that also supports host
reservation, has to perform additional checks: not only if the address is
currently used (i.e. if there is a lease for it), but also whether the
address could be used by someone else (i.e. if there is a reservation for
it). That additional check incurs additional overhead.
9.3.1. Address/Prefix Reservation Types
In a typical scenario there is an IPv6 subnet defined with a certain part
of it dedicated for dynamic address allocation by the DHCPv6 server. There
may be an additional address space defined for prefix delegation. Those
dynamic parts are referred to as dynamic pools, address and prefix pools
or simply pools. In principle, the host reservation can reserve any
address or prefix that belongs to the subnet. The reservations that
specify an address that belongs to configured pools are called "in-pool
reservations". In contrast, those that do not belong to dynamic pools are
called "out-of-pool reservations". There is no formal difference in the
reservation syntax and both reservation types are handled uniformly.
However, upcoming releases may offer improved performance if there are
only out-of-pool reservations as the server will be able to skip
reservation checks when dealing with existing leases. Therefore, system
administrators are encouraged to use out-of-pool reservations if possible.
9.3.2. Conflicts in DHCPv6 Reservations
As reservations and lease information are stored separately, conflicts may
arise. Consider the following series of events. The server has configured
the dynamic pool of addresses from the range of 2001:db8::10 to
2001:db8::20. Host A requests an address and gets 2001:db8::10. Now the
system administrator decides to reserve address 2001:db8::10 for Host B.
In general, reserving an address that is currently assigned to someone
else is not recommended, but there are valid use cases where such an
operation is warranted.
The server now has a conflict to resolve. Let's analyze the situation
here. If Host B boots up and request an address, the server is not able to
assign the reserved address 2001:db8::10. A naive approach would to be
immediately remove the lease for Host A and create a new one for Host B.
That would not solve the problem, though, because as soon as Host B get
the address, it will detect that the address is already in use by someone
else (Host A) and would send a Decline message. Therefore in this
situation, the server has to temporarily assign a different address from
the dynamic pool (not matching what has been reserved) to Host B.
When Host A renews its address, the server will discover that the address
being renewed is now reserved for someone else (Host B). Therefore the
server will remove the lease for 2001:db8::10, select a new address and
create a new lease for it. It will send two addresses in its response: the
old address with lifetime set to 0 to explicitly indicate that it is no
longer valid and the new address with a non-zero lifetime. When Host B
renews its temporarily assigned address, the server will detect that the
existing lease does not match reservation, so it will release the current
address Host B has and will create a new lease matching the reservation.
Similar as before, the server will send two addresses: the temporarily
assigned one with zeroed lifetimes, and the new one that matches
reservation with proper lifetimes set.
This recovery will succeed, even if other hosts will attempt to get the
reserved address. Had Host C requested address 2001:db8::10 after the
reservation was made, the server will propose a different address.
This recovery mechanism allows the server to fully recover from a case
where reservations conflict with existing leases. This procedure takes
time and will roughly take as long as renew-timer value specified. The
best way to avoid such recovery is to not define new reservations that
conflict with existing leases. Another recommendation is to use
out-of-pool reservations. If the reserved address does not belong to a
pool, there is no way that other clients could get this address.
9.3.3. Reserving a Hostname
When the reservation for the client includes the hostname, the server will
assign this hostname to the client and send it back in the Client FQDN, if
the client sent the FQDN option to the server. The reserved hostname
always takes precedence over the hostname supplied by the client (via the
FQDN option) or the autogenerated (from the IPv6 address) hostname.
The server qualifies the reserved hostname with the value of the
qualifying-suffix parameter. For example, the following subnet
configuration:
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "alice-laptop"
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example.isc.org."
}
will result in assigning the "alice-laptop.example.isc.org." hostname to
the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the
qualifying-suffix is not specified, the default (empty) value will be
used, and in this case the value specified as a hostname will be treated
as fully qualified name. Thus, by leaving the qualifying-suffix empty it
is possible to qualify hostnames for the different clients with different
domain names:
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "mark-desktop.example.org."
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
}
The above example results in the assignment of the
"mark-desktop.example.org." hostname to the client using the DUID
"01:02:03:04:05:0A:0B:0C:0D:0E".
9.3.4. Including Specific DHCPv6 Options in Reservations
Kea 1.1.0 introduced the ability to specify options on a per host basis.
The options follow the same rules as any other options. These can be
standard options (see Section 9.2.10, "Standard DHCPv6 Options"), custom
options (see Section 9.2.12, "Custom DHCPv6 Options") or vendor specific
options (see Section 9.2.13, "DHCPv6 Vendor-Specific Options"). The
following example demonstrates how standard options can be defined.
"reservations": [
{
"duid": "01:02:03:05:06:07:08",
"ip-addresses": [ "2001:db8:1::2" ],
"option-data": [
{
"option-data": [ {
"name": "dns-servers",
"data": "3000:1::234"
},
{
"name": "nis-servers",
"data": "3000:1::234"
}
} ]
} ]
Vendor specific options can be reserved in a similar manner:
"reservations": [
{
"duid": "aa:bb:cc:dd:ee:ff",
"ip-addresses": [ "2001:db8::1" ],
"option-data": [
{
"name": "vendor-opts",
"data": 4491
},
{
"name": "tftp-servers",
"space": "vendor-4491",
"data": "3000:1::234"
} ]
} ]
Options defined on host level have the highest priority. In other words,
if there are options defined with the same type on global, subnet, class
and host level, the host specific values will be used.
9.3.5. Reserving Client Classes in DHCPv6
The Section 13.3, "Using Expressions In Classification" explains how to
configure the server to assign classes to a client based on the content of
the options that this client sends to the server. Host reservations
mechanisms also allow for the static assignment of classes to clients. The
definitions of these classes are placed in the Kea configuration. The
following configuration snippet shows how to specify that the client
belongs to classes reserved-class1 and reserved-class2. Those classes are
associated with specific options being sent to the clients which belong to
them.
{
"client-classes": [
{
"name": "reserved-class1",
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:1::50"
}
]
},
{
"name": "reserved-class2",
"option-data": [
{
"name": "nis-servers",
"data": "2001:db8:1::100"
}
]
}
],
"subnet6": [
{ "pools": [ { "pool": "2001:db8:1::/64" } ],
"subnet": "2001:db8:1::/48",
"reservations": [
{
"duid": "01:02:03:04:05:06:07:08",
"client-classes": [ "reserved-class1", "reserved-class2" ]
} ]
} ]
}
Static class assignments, as shown above, can be used in conjunction with
classification using expressions. The "KNOWN" or "UNKNOWN" builtin class
is added to the packet and any class depending on it directly or
indirectly and not only-if-required is evaluated.
Note
If you want to force the evaluation of a class expression after the host
reservation lookup, for instance because of a dependency on
"reserved-class1" from the previous example, you should add a
"member('KNOWN')" in the expression.
9.3.6. Storing Host Reservations in MySQL, PostgreSQL or Cassandra
It is possible to store host reservations in MySQL, PostgreSQL or
Cassandra. See Section 9.2.3, "Hosts Storage" for information on how to
configure Kea to use reservations stored in MySQL, PostgreSQL or
Cassandra. Kea provides dedicated hook for managing reservations in a
database, section Section 14.4.4, "host_cmds: Host Commands" provide
detailed information. The Kea wiki
http://kea.isc.org/wiki/HostReservationsHowTo provides some examples how
to conduct some common operations on host reservations.
Note
In Kea maximum length of an option specified per host is arbitrarily set
to 4096 bytes.
9.3.7. Fine Tuning DHCPv6 Host Reservation
The host reservation capability introduces additional restrictions for the
allocation engine (the component of Kea that selects an address for a
client) during lease selection and renewal. In particular, three major
checks are necessary. First, when selecting a new lease, it is not
sufficient for a candidate lease to not be used by another DHCP client. It
also must not be reserved for another client. Second, when renewing a
lease, additional check must be performed whether the address being
renewed is not reserved for another client. Finally, when a host renews an
address or a prefix, the server has to check whether there is a
reservation for this host, so the existing (dynamically allocated) address
should be revoked and the reserved one be used instead.
Some of those checks may be unnecessary in certain deployments and not
performing them may improve performance. The Kea server provides the
reservation-mode configuration parameter to select the types of
reservations allowed for the particular subnet. Each reservation type has
different constraints for the checks to be performed by the server when
allocating or renewing a lease for the client. Allowed values are:
* all - enables all host reservation types. This is the default value.
This setting is the safest and the most flexible. It allows in-pool
and out-of-pool reservations. As all checks are conducted, it is also
the slowest.
* out-of-pool - allows only out of pool host reservations. With this
setting in place, the server may assume that all host reservations are
for addresses that do not belong to the dynamic pool. Therefore it can
skip the reservation checks when dealing with in-pool addresses, thus
improving performance. Do not use this mode if any of your
reservations use in-pool address. Caution is advised when using this
setting. Kea does not sanity check the reservations against
reservation-mode and misconfiguration may cause problems.
* disabled - host reservation support is disabled. As there are no
reservations, the server will skip all checks. Any reservations
defined will be completely ignored. As the checks are skipped, the
server may operate faster in this mode.
An example configuration that disables reservation looks like follows:
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"reservation-mode": "disabled",
...
}
]
}
Another aspect of the host reservations are different types of
identifiers. Kea 1.1.0 supports two types of identifiers in DHCPv6:
hw-address and duid, but more identifier types are likely to be added in
the future. This is beneficial from a usability perspective. However,
there is a drawback. For each incoming packet Kea has to to extract each
identifier type and then query the database to see if there is a
reservation done by this particular identifier. If nothing is found, the
next identifier is extracted and next query is issued. This process
continues until either a reservation is found or all identifier types have
been checked. Over time with an increasing number of supported identifier
types, Kea would become slower and slower.
To address this problem, a parameter called host-reservation-identifiers
has been introduced. It takes a list of identifier types as a parameter.
Kea will check only those identifier types enumerated in
host-reservation-identifiers. From a performance perspective the number of
identifier types should be kept to minimum, ideally limited to one. If
your deployment uses several reservation types, please enumerate them from
most to least frequently used as this increases the chances of Kea finding
the reservation using the fewest number of queries. An example of host
reservation identifiers looks as follows:
"host-reservation-identifiers": [ "duid", "hw-address" ],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
...
}
]
If not specified, the default value is:
"host-reservation-identifiers": [ "hw-address", "duid" ]
9.4. Shared networks in DHCPv6
DHCP servers use subnet information in two ways. First, it is used to
determine the point of attachment, or simply put, where the client is
connected to the network. Second, the subnet information is used to group
information pertaining to specific location in the network. This approach
works well in general case, but the are scenarios where the boundaries are
blurred. Sometimes it is useful to have more than one logical IP subnet
being deployed on the same physical link. The need to understand that two
or more subnets are used on the same link requires additional logic in the
DHCP server. This capability has been added in Kea 1.3.0. It is called
"shared networks" in Kea and ISC DHCP projects. It is sometimes also
called "shared subnets". In Microsoft's nomenclature it is called
"multinet".
There are many use cases where the feature is useful. The most common
example in the IPv4 case is when the server is running out of available
addresses in a subnet. This is less common in IPv6, but the shared
networks are still useful in IPv6. One of the use cases is an exhaustion
of IPv6 delegated prefixes within a subnet. Another IPv6 specific example
is an experiment with addressing scheme. With the advent of IPv6
deployment and vast address space, many organizations split the address
space into subnets, then deploy it and after a while discover that they
want to split it differently. In the transition period they want both old
and new addressing to be available. Thus the need for more than one subnet
on the same physical link.
Finally, the case of cable networks is directly applicable in IPv6. There
are two types of devices in cable networks: cable modems and the end user
devices behind them. It is a common practice to use different subnet for
cable modems to prevent users from tinkering with their cable modems. In
this case, the distinction is based on the type of device, rather than
coming out of running out address space.
A client connected to a shared network may be assigned a lease (address or
prefix) from any of the pools defined within the subnets belonging to the
shared network. Internally, the server selects one of the subnets
belonging to the shared network and tries to allocate a lease from this
subnet. If the server is unable to allocate a lease from the selected
subnet (e.g. due to pools exhaustion) it will use another subnet from the
same shared network and try to allocate a lease from this subnet etc.
Therefore, in the typical case, the server will allocate all leases
available in a given subnet before it starts allocating leases from other
subnets belonging to the same shared network. However, in certain
situations the client can be allocated a lease from the other subnets
before the pools in the first subnet get exhausted, e.g. when the client
provides a hint that belongs to another subnet or the client has
reservations in a different than default subnet.
Note
It is strongly discouraged for the Kea deployments to assume that the
server doesn't allocate leases from other subnets until it uses all the
leases from the first subnet in the shared network. Apart from the fact
that hints, host reservations and client classification affect subnet
selection, it is also foreseen that we will enhance allocation strategies
for shared networks in the future versions of Kea, so as the selection of
subnets within a shared network is equally probable (unpredictable).
In order to define a shared network an additional configuration scope is
introduced:
{
"Dhcp6": {
"shared-networks": [
{
// Name of the shared network. It may be an arbitrary string
// and it must be unique among all shared networks.
"name": "ipv6-lab-1",
// Subnet selector can be specifed on the shared network level.
// Subnets from this shared network will be selected for clients
// communicating via relay agent having the specified IP address.
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
// This starts a list of subnets in this shared network.
// There are two subnets in this example.
"subnet6": [
{
"subnet": "2001:db8::/48",
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ]
},
{
"subnet": "3ffe:ffe::/64",
"pools": [ { "pool": "3ffe:ffe::/64" } ]
}
]
} ], // end of shared-networks
// It is likely that in your network you'll have a mix of regular,
// "plain" subnets and shared networks. It is perfectly valid to mix
// them in the same config file.
//
// This is regular subnet. It's not part of any shared-network.
"subnet6": [
{
"subnet": "2001:db9::/48",
"pools": [ { "pool": "2001:db9::/64" } ],
"relay": {
"ip-addresses": [ "2001:db8:1:2::1" ]
}
}
]
} // end of Dhcp6
}
As you see in the example, it is possible to mix shared and regular
("plain") subnets. Each shared network must have a unique name. This is a
similar concept to ID for subnets, but it offers more flexibility. This is
used for logging, but also internally for identifying shared networks.
In principle it makes sense to define only shared networks that consist of
two or more subnets. However, for testing purposes it is allowed to define
a shared network with just one subnet or even an empty one. This is not a
recommended practice in production networks, as the shared network logic
requires additional processing and thus lowers server's performance. To
avoid unnecessary performance degradation the shared subnets should only
be defined when required by the deployment.
Shared networks provide an ability to specify many parameters in the
shared network scope that will apply to all subnets within it. If
necessary, you can specify a parameter in the shared network scope and
then override its value on the subnet scope. For example:
"shared-networks": [
{
"name": "lab-network3",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
// This applies to all subnets in this shared network, unless
// values are overridden on subnet scope.
"valid-lifetime": 600,
// This option is made available to all subnets in this shared
// network.
"option-data": [ {
"name": "dns-servers",
"data": "2001:db8::8888"
} ],
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::1 - 2001:db8:1::ffff" } ],
// This particular subnet uses different values.
"valid-lifetime": 1200,
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8::1:2"
},
{
"name": "unicast",
"data": "2001:abcd::1"
} ]
},
{
"subnet": "2001:db8:2::/48",
"pools": [ { "pool": "2001:db8:2::1 - 2001:db8:2::ffff" } ],
// This subnet does not specify its own valid-lifetime value,
// so it is inherited from shared network scope.
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:cafe::1"
} ]
}
],
} ]
In this example, there is a dns-servers option defined that is available
to clients in both subnets in this shared network. Also, a valid lifetime
is set to 10 minutes (600s). However, the first subnet overrides some of
the values (valid lifetime is 20 minutes, different IP address for
dns-servers), but also adds its own option (unicast address). Assuming a
client asking for a server unicast and dns servers options is assigned a
lease from this subnet, he will get a lease for 20 minutes and dns-servers
and be allowed to use server unicast at address 2001:abcd::1. If the same
client is assigned to the second subnet, he will get a 10 minutes long
lease, dns-servers value of 2001:db8:cafe::1 and no server unicast.
Some parameters must be the same in all subnets in the same shared
network. This restriction applies to interface and rapid-commit settings.
The most convenient way is to define them on shared network scope, but you
may specify them for each subnet. However, care should be taken for each
subnet to have the same value.
9.4.1. Local and relayed traffic in shared networks
It is possible to specify interface name in the shared network scope to
tell the server that this specific shared network is reachable directly
(not via relays) using local network interface. It is sufficient to
specify it once in the shared network level. As all subnets in a shared
network are expected to be used on the same physical link, it is a
configuration error to attempt to make a shared network out of subnets
that are reachable over different interfaces. It is allowed to specify
interface parameter on each subnet, although its value must be the same
for each subnet. Thus it's usually more convenient to specify it once on
the shared network level.
"shared-networks": [
{
"name": "office-floor-2",
// This tells Kea that the whole shared networks is reachable over
// local interface. This applies to all subnets in this network.
"interface": "eth0",
"subnet6": [
{
"subnet": "2001:db8::/64",
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ],
"interface": "eth0"
},
{
"subnet": "3ffe:abcd::/64",
"pools": [ { "pool": "3ffe:abcd::1 - 3ffe:abcd::ffff" } ]
// Specifying a different interface name is configuration
// error:
// "interface": "eth1"
}
],
} ]
Somewhat similar to interface names, also relay IP addresses can be
specified for the whole shared network. However, depending on your relay
configuration, it may use different IP addresses depending on which subnet
is being used. Thus there is no requirement to use the same IP relay
address for each subnet. Here's an example:
"shared-networks": [
{
"name": "kakapo",
"relay": {
"ip-addresses": [ "2001:db8::abcd" ]
},
"subnet6": [
{
"subnet": "2001:db8::/64",
"relay": {
"ip-addresses": [ "2001:db8::1234" ]
},
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ]
},
{
"subnet": "3ffe:abcd::/64",
"pools": [ { "pool": "3ffe:abcd::1 - 3ffe:abcd::ffff" } ],
"relay": {
"ip-addresses": [ "3ffe:abcd::cafe" ]
}
}
]
}
]
In this particular case the relay IP address specified on network level
doesn't have much sense, as it is overridden in both subnets, but it was
left there as an example of how one could be defined on network level.
Note that the relay agent IP address typically belongs to the subnet it
relays packets from, but this is not a strict requirement. Therefore Kea
accepts any value here as long as it is valid IPv6 address.
9.4.2. Client classification in shared networks
Sometimes it is desired to segregate clients into specific subnets based
on some properties. This mechanism is called client classification and is
described in Chapter 13, Client Classification. Client classification can
be applied to subnets belonging to shared networks in the same way as it
is used for subnets specified outside of shared networks. It is important
to understand how the server selects subnets for the clients when client
classification is in use, to assure that the desired subnet is selected
for a given client type.
If a subnet is associated with some classes, only the clients belonging to
any of these classes can use this subnet. If there are no classes
specified for a subnet, any client connected to a given shared network can
use this subnet. A common mistake is to assume that the subnet including
client classes is preferred over subnets without client classes. Consider
the following example:
{
"client-classes": [
{
"name": "b-devices",
"test": "option[1234].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"relay": {
"ip-address": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
},
{
"subnet": "2001:db8:3::/64",
"pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
"client-class": "b-devices"
}
]
}
]
}
If the client belongs to "b-devices" class (because it includes option
1234 with a value of 0x0002) it doesn't guarantee that the subnet
2001:db8:3::/64 will be used (or preferred) for this client. The server
can use any of the two subnets because the subnet 2001:db8:1::/64 is also
allowed for this client. The client classification used in this case
should be pereceived as a way to restrict access to certain subnets,
rather than a way to express subnet preference. For example, if the client
doesn't belong to the "b-devices" class it may only use the subnet
2001:db8:1::/64 and will never use the subnet 2001:db8:3::/64.
A typical use case for client classification is in the cable network,
where cable modems should use one subnet and other devices should use
another subnet within the same shared network. In this case it is required
to apply classification on all subnets. The following example defines two
classes of devices. The subnet selection is made based on option 1234
values.
{
"client-classes": [
{
"name": "a-devices",
"test": "option[1234].hex == 0x0001"
},
{
"name": "b-devices",
"test": "option[1234].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
"client-class": "a-devices"
},
{
"subnet": "2001:db8:3::/64",
"pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
"client-class": "b-devices"
}
]
}
]
}
In this example each class has its own restriction. Only clients that
belong to class a-devices will be able to use subnet 2001:db8:1::/64 and
only clients belonging to b-devices will be able to use subnet
2001:db8:3::/64. Care should be taken to not define too restrictive
classification rules, as clients that are unable to use any subnets will
be refused service. Although, this may be desired outcome if one desires
to service only clients of known properties (e.g. only VoIP phones allowed
on a given link).
Note that it is possible to achieve similar effect as presented in this
section without the use of shared networks. If the subnets are placed in
the global subnets scope, rather than in the shared network, the server
will still use classification rules to pick the right subnet for a given
class of devices. The major benefit of placing subnets within the shared
network is that common parameters for the logically grouped subnets can be
specified once, in the shared network scope, e.g. "interface" or "relay"
parameter. All subnets belonging to this shared network will inherit those
parameters.
9.4.3. Host reservations in shared networks
Subnets being part of a shared network allow host reservations, similar to
regular subnets:
{
"shared-networks": [
{
"name": "frog",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"id": 100,
"pools": [ { "2001:db8:1::1 - 2001:db8:1::64" } ],
"reservations": [
{
"duid": "00:03:00:01:11:22:33:44:55:66",
"ip-addresses": [ "2001:db8:1::28" ]
}
]
},
{
"subnet": "2001:db8:3::/64",
"id": 101,
"pools": [ { "pool": "2001:db8:3::1 - 2001:db8:3::64" } ],
"reservations": [
{
"duid": "00:03:00:01:aa:bb:cc:dd:ee:ff",
"ip-addresses": [ "2001:db8:2::28" ]
}
]
}
]
}
]
}
It is worth noting that Kea conducts additional checks when processing a
packet if shared networks are defined. First, instead of simply checking
if there's a reservation for a given client in his initially selected
subnet, it goes through all subnets in a shared network looking for a
reservation. This is one of the reasons why defining a shared network may
impact performance. If there is a reservation for a client in any subnet,
that particular subnet will be picked for the client. Although it's
technically not an error, it is considered a bad practice to define
reservations for the same host in multiple subnets belonging to the same
shared network.
While not strictly mandatory, it is strongly recommended to use explicit
"id" values for subnets if you plan to use database storage for host
reservations. If ID is not specified, the values for it be autogenerated,
i.e. it will assign increasing integer values starting from 1. Thus, the
autogenerated IDs are not stable across configuration changes.
9.5. Server Identifier in DHCPv6
The DHCPv6 protocol uses a "server identifier" (also known as a DUID) for
clients to be able to discriminate between several servers present on the
same link. RFC 3315 defines three DUID types: DUID-LLT, DUID-EN and
DUID-LL. RFC 6355 also defines DUID-UUID. Future specifications may
introduce new DUID types.
The Kea DHCPv6 server generates a server identifier once, upon the first
startup, and stores it in a file. This identifier isn't modified across
restarts of the server and so is a stable identifier.
Kea follows recommendation from RFC 3315 to use DUID-LLT as the default
server identifier. However, we have received reports that some deployments
require different DUID types, and there is a need to administratively
select both DUID type and/or its contents.
The server identifier can be configured using parameters within the
server-id map element in the global scope of the Kea configuration file.
The following example demonstrates how to select DUID-EN as a server
identifier:
"Dhcp6": {
"server-id": {
"type": "EN"
},
...
}
Currently supported values for type parameter are: "LLT", "EN" and "LL",
for DUID-LLT, DUID-EN and DUID-LL respectively.
When a new DUID type is selected the server will generate its value and
replace any existing DUID in the file. The server will then use the new
server identifier in all future interactions with the clients.
Note
If the new server identifier is created after some clients have obtained
their leases, the clients using the old identifier will not be able to
renew the leases: the server will ignore messages containing the old
server identifier. Clients will continue sending Renew until they
transition to the rebinding state. In this state they will start sending
Rebind messages to multicast address without a server identifier. The
server will respond to the Rebind messages with a new server identifier
and the clients will associate the new server identifier with their
leases. Although the clients will be able to keep their leases and will
eventually learn the new server identifier, this will be at the cost of
increased number of renewals and multicast traffic due to a need to
rebind. Therefore it is recommended that modification of the server
identifier type and value is avoided if the server has already assigned
leases and these leases are still valid.
There are cases when an administrator needs to explicitly specify a DUID
value rather than allow the server to generate it. The following example
demonstrates how to explicitly set all components of a DUID-LLT.
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 8,
"identifier": "A65DC7410F05",
"time": 2518920166
},
...
}
where:
* htype is a 16-bit unsigned value specifying hardware type,
* identifier is a link layer address, specified as a string of
hexadecimal digits,
* time is a 32-bit unsigned time value.
The hexadecimal representation of the DUID generated as a result of the
configuration specified above will be:
00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
|type |htype| time | identifier |
It is allowed to use special value of 0 for "htype" and "time", which
indicates that the server should use ANY value for these components. If
the server already uses a DUID-LLT it will use the values from this DUID.
If the server uses a DUID of a different type or doesn't use any DUID yet,
it will generate these values. Similarly, if the "identifier" is assigned
an empty string, the value of the identifier will be generated. Omitting
any of these parameters is equivalent to setting them to those special
values.
For example, the following configuration:
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 0,
"identifier": "",
"time": 2518920166
},
...
}
indicates that the server should use ANY link layer address and hardware
type. If the server is already using DUID-LLT it will use the link layer
address and hardware type from the existing DUID. If the server is not
using any DUID yet, it will use link layer address and hardware type from
one of the available network interfaces. The server will use an explicit
value of time. If it is different than a time value present in the
currently used DUID, that value will be replaced, effectively causing
modification of the current server identifier.
The following example demonstrates an explicit configuration of a DUID-EN:
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545"
},
...
}
where:
* enterprise-id is a 32-bit unsigned value holding enterprise number,
* identifier is a variable length identifier within DUID-EN.
The hexadecimal representation of the DUID-EN created according to the
configuration above is:
00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
|type | ent-id | identifier |
As in the case of the DUID-LLT, special values can be used for the
configuration of the DUID-EN. If enterprise-id is 0, the server will use a
value from the existing DUID-EN. If the server is not using any DUID or
the existing DUID has a different type, the ISC enterprise id will be
used. When an empty string is used for identifier, the identifier from the
existing DUID-EN will be used. If the server is not using any DUID-EN the
new 6-bytes long identifier will be generated.
DUID-LL is configured in the same way as DUID-LLT with an exception that
the time parameter has no effect for DUID-LL, because this DUID type only
comprises a hardware type and link layer address. The following example
demonstrates how to configure DUID-LL:
"Dhcp6": {
"server-id": {
"type": "LL",
"htype": 8,
"identifier": "A65DC7410F05"
},
...
}
which will result in the following server identifier:
00:03:00:08:A6:5D:C7:41:0F:05
|type |htype| identifier |
The server stores the generated server identifier in the following
location: [kea-install-dir]/var/kea/kea-dhcp6-serverid.
In some uncommon deployments where no stable storage is available, the
server should be configured not to try to store the server identifier.
This choice is controlled by the value of persist boolean parameter:
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545",
"persist": false
},
...
}
The default value of the "persist" parameter is true which configures the
server to store the server identifier on a disk.
In the example above, the server is configured to not store the generated
server identifier on a disk. But, if the server identifier is not modified
in the configuration the same value will be used after server restart,
because entire server identifier is explicitly specified in the
configuration.
9.6. Stateless DHCPv6 (Information-Request Message)
Typically DHCPv6 is used to assign both addresses and options. These
assignments (leases) have state that changes over time, hence their name,
stateful. DHCPv6 also supports a stateless mode, where clients request
configuration options only. This mode is considered lightweight from the
server perspective as it does not require any state tracking; hence its
name.
The Kea server supports stateless mode. Clients can send
Information-Request messages and the server will send back answers with
the requested options (providing the options are available in the server
configuration). The server will attempt to use per-subnet options first.
If that fails - for whatever reason - it will then try to provide options
defined in the global scope.
Stateless and stateful mode can be used together. No special configuration
directives are required to handle this. Simply use the configuration for
stateful clients and the stateless clients will get just options they
requested.
This usage of global options allows for an interesting case. It is
possible to run a server that provides just options and no addresses or
prefixes. If the options have the same value in each subnet, the
configuration can define required options in the global scope and skip
subnet definitions altogether. Here's a simple example of such a
configuration:
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "ethX" ]
},
"option-data": [ {
"name": "dns-servers",
"data": "2001:db8::1, 2001:db8::2"
} ],
"lease-database": { "type": "memfile" }
}
This very simple configuration will provide DNS server information to all
clients in the network, regardless of their location. Note the
specification of the memfile lease database: this is needed as Kea
requires a lease database to be specified even if it is not used.
9.7. Support for RFC 7550
The RFC 7550 introduced some changes to the DHCPv6 protocol to resolve a
few issues with the coexistence of multiple stateful options in the
messages sent between the clients and servers.
The typical example is when the client, such as a requesting router,
requests an allocation of both addresses and prefixes when it performs the
4-way (SARR) exchange with the server. If the server is not configured to
allocate any prefixes but it can allocate some addresses, it will respond
with the IA_NA(s) containing allocated addresses and the IA_PD(s)
containing the NoPrefixAvail status code. If the client can operate
without prefixes it may transition to the 'bound' state when it sends
Renew/Rebind messages to the server, according to the T1 and T2 times, to
extend the lifetimes of the allocated addresses. If the client is still
interested in obtaining prefixes from the server it may also include an
IA_PD in the Renew/Rebind to request allocation of the prefixes. If the
server still cannot allocate the prefixes, it will respond with the
IA_PD(s) containing NoPrefixAvail status code. However, if the server can
now allocate the prefixes it will do so, and send them in the IA_PD(s) to
the client. Allocation of leases during the Renew/Rebind was not supported
in the RFC 3315 and RFC 3633, and has been introduced in RFC 7550. Kea
supports this new behavior and it doesn't provide any configuration
mechanisms to disable it.
The following are the other behaviors specified in the RFC 7550 supported
by the Kea DHCPv6 server:
* Set T1/T2 timers to the same value for all stateful (IA_NA and IA_PD)
options to facilitate renewal of all client's leases at the same time
(in a single message exchange),
* NoAddrsAvail and NoPrefixAvail status codes are placed in the IA_NA
and IA_PD options in the Advertise message, rather than as the top
level options.
9.8. Using Specific Relay Agent for a Subnet
The relay has to have an interface connected to the link on which the
clients are being configured. Typically the relay has a global IPv6
address configured on the interface that belongs to the subnet from which
the server will assign addresses. In the typical case, the server is able
to use the IPv6 address inserted by the relay (in the link-addr field in
RELAY-FORW message) to select the appropriate subnet.
However, that is not always the case. The relay address may not match the
subnet in certain deployments. This usually means that there is more than
one subnet allocated for a given link. The two most common examples where
this is the case are long lasting network renumbering (where both old and
new address space is still being used) and a cable network. In a cable
network both cable modems and the devices behind them are physically
connected to the same link, yet they use distinct addressing. In such
case, the DHCPv6 server needs additional information (like the value of
interface-id option or IPv6 address inserted in the link-addr field in
RELAY-FORW message) to properly select an appropriate subnet.
The following example assumes that there is a subnet 2001:db8:1::/64 that
is accessible via a relay that uses 3000::1 as its IPv6 address. The
server will be able to select this subnet for any incoming packets that
came from a relay with an address in 2001:db8:1::/64 subnet. It will also
select that subnet for a relay with address 3000::1.
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
"relay": {
"ip-addresses": [ "3000::1" ]
}
}
]
}
If "relay" is specified, the "ip-addresses" parameter within it is
mandatory.
Note
As of Kea 1.4, the "ip-address" parameter in "relay" has been deprecated
in favor of "ip-addresses" which supports specifying a list of addresses.
Configuration parsing, will honor the singular form for now but users are
encouraged to migrate.
9.9. Segregating IPv6 Clients in a Cable Network
In certain cases, it is useful to mix relay address information,
introduced in Section 9.8, "Using Specific Relay Agent for a Subnet" with
client classification, explained in Chapter 13, Client Classification. One
specific example is a cable network, where typically modems get addresses
from a different subnet than all devices connected behind them.
Let's assume that there is one CMTS (Cable Modem Termination System) with
one CM MAC (a physical link that modems are connected to). We want the
modems to get addresses from the 3000::/64 subnet, while everything
connected behind modems should get addresses from another subnet
(2001:db8:1::/64). The CMTS that acts as a relay an uses address 3000::1.
The following configuration can serve that configuration:
"Dhcp6": {
"subnet6": [
{
"subnet": "3000::/64",
"pools": [
{ "pool": "3000::2 - 3000::ffff" }
],
"client-class": "VENDOR_CLASS_docsis3.0",
"relay": {
"ip-addresses": [ "3000::1" ]
}
},
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
"relay": {
"ip-addresses": [ "3000::1" ]
}
}
]
}
9.10. MAC/Hardware Addresses in DHCPv6
MAC/hardware addresses are available in DHCPv4 messages from the clients
and administrators frequently use that information to perform certain
tasks, like per host configuration, address reservation for specific MAC
addresses and other. Unfortunately, the DHCPv6 protocol does not provide
any completely reliable way to retrieve that information. To mitigate that
issue a number of mechanisms have been implemented in Kea that attempt to
gather it. Each of those mechanisms works in certain cases, but may fail
in other cases. Whether the mechanism works or not in the particular
deployment is somewhat dependent on the network topology and the
technologies used.
Kea allows configuration of which of the supported methods should be used
and in what order. This configuration may be considered a fine tuning of
the DHCP deployment. In a typical deployment the default value of "any" is
sufficient and there is no need to select specific methods. Changing the
value of this parameter is the most useful in cases when an administrator
wants to disable certain method, e.g. if the administrator trusts the
network infrastructure more than the information provided by the clients
themselves, the administrator may prefer information provided by the
relays over that provided by the clients.
The configuration is controlled by the mac-sources parameter as follows:
"Dhcp6": {
"mac-sources": [ "method1", "method2", "method3", ... ],
"subnet6": [ ... ],
...
}
When not specified, a special value of "any" is used, which instructs the
server to attempt to use all the methods in sequence and use value
returned by the first one that succeeds. If specified, it has to have at
least one value.
Supported methods are:
* any - Not an actual method, just a keyword that instructs Kea to try
all other methods and use the first one that succeeds. This is the
default operation if no mac-sources are defined.
* raw - In principle, a DHCPv6 server could use raw sockets to receive
incoming traffic and extract MAC/hardware address information. This is
currently not implemented for DHCPv6 and this value has no effect.
* duid - DHCPv6 uses DUID identifiers instead of MAC addresses. There
are currently four DUID types defined, with two of them (DUID-LLT,
which is the default one and DUID-LL) convey MAC address information.
Although RFC 3315 forbids it, it is possible to parse those DUIDs and
extract necessary information from them. This method is not completely
reliable, as clients may use other DUID types, namely DUID-EN or
DUID-UUID.
* ipv6-link-local - Another possible acquisition method comes from the
source IPv6 address. In typical usage, clients are sending their
packets from IPv6 link-local addresses. There is a good chance that
those addresses are based on EUI-64, which contains MAC address. This
method is not completely reliable, as clients may use other link-local
address types. In particular, privacy extensions, defined in RFC 4941,
do not use MAC addresses. Also note that successful extraction
requires that the address's u-bit must be set to 1 and its g-bit set
to 0, indicating that it is an interface identifier as per RFC 2373,
section 2.5.1.
* client-link-addr-option - One extension defined to alleviate missing
MAC issues is client link-layer address option, defined in RFC 6939.
This is an option that is inserted by a relay and contains information
about client's MAC address. This method requires a relay agent that
supports the option and is configured to insert it. This method is
useless for directly connected clients. This parameter can also be
specified as rfc6939, which is an alias for client-link-addr-option.
* remote-id - RFC 4649 defines a remote-id option that is inserted by a
relay agent. Depending on the relay agent configuration, the inserted
option may convey the client's MAC address information. This parameter
can also be specified as rfc4649, which is an alias for remote-id.
* subscriber-id - Another option that is somewhat similar to the
previous one is subscriber-id, defined in RFC 4580. It is, too,
inserted by a relay agent that is configured to insert it. This
parameter can also be specified as rfc4580, which is an alias for
subscriber-id. This method is currently not implemented.
* docsis-cmts - Yet another possible source of MAC address information
are the DOCSIS options inserted by a CMTS that acts as a DHCPv6 relay
agent in cable networks. This method attempts to extract MAC address
information from suboption 1026 (cm mac) of the vendor specific option
with vendor-id=4491. This vendor option is extracted from the
relay-forward message, not the original client's message.
* docsis-modem - Yet another possible source of MAC address information
are the DOCSIS options inserted by the cable modem itself. This method
attempts to extract MAC address information from suboption 36 (device
id) of the vendor specific option with vendor-id=4491. This vendor
option is extracted from the original client's message, not from any
relay options.
Empty mac-sources is not allowed. If you do not want to specify it, either
simply omit mac-sources definition or specify it with the "any" value
which is the default.
9.11. Duplicate Addresses (DECLINE Support)
The DHCPv6 server is configured with a certain pool of addresses that it
is expected to hand out to the DHCPv6 clients. It is assumed that the
server is authoritative and has complete jurisdiction over those
addresses. However, due to various reasons, such as misconfiguration or a
faulty client implementation that retains its address beyond the valid
lifetime, there may be devices connected that use those addresses without
the server's approval or knowledge.
Such an unwelcome event can be detected by legitimate clients (using
Duplicate Address Detection) and reported to the DHCPv6 server using a
DECLINE message. The server will do a sanity check (if the client
declining an address really was supposed to use it), then will conduct a
clean up operation and confirm it by sending back a REPLY message. Any DNS
entries related to that address will be removed, the fact will be logged
and hooks will be triggered. After that is done, the address will be
marked as declined (which indicates that it is used by an unknown entity
and thus not available for assignment to anyone) and a probation time will
be set on it. Unless otherwise configured, the probation period lasts 24
hours. After that period, the server will recover the lease (i.e. put it
back into the available state) and the address will be available for
assignment again. It should be noted that if the underlying issue of a
misconfigured device is not resolved, the duplicate address scenario will
repeat. On the other hand, it provides an opportunity to recover from such
an event automatically, without any sysadmin intervention.
To configure the decline probation period to a value other than the
default, the following syntax can be used:
"Dhcp6": {
"decline-probation-period": 3600,
"subnet6": [ ... ],
...
}
The parameter is expressed in seconds, so the example above will instruct
the server to recycle declined leases after an hour.
There are several statistics and hook points associated with the Decline
handling procedure. The lease6_decline hook is triggered after the
incoming Decline message has been sanitized and the server is about to
decline the lease. The declined-addresses statistic is increased after the
hook returns (both global and subnet specific variants). (See Section 8.8,
"Statistics in the DHCPv4 Server" and Chapter 14, Hooks Libraries for more
details on DHCPv4 statistics and Kea hook points.)
Once the probation time elapses, the declined lease is recovered using the
standard expired lease reclamation procedure, with several additional
steps. In particular, both declined-addresses statistics (global and
subnet specific) are decreased. At the same time,
reclaimed-declined-addresses statistics (again in two variants, global and
subnet specific) are increased.
Note about statistics: The server does not decrease the assigned-addresses
statistics when a DECLINE message is received and processed successfully.
While technically a declined address is no longer assigned, the primary
usage of the assigned-addresses statistic is to monitor pool utilization.
Most people would forget to include declined-addresses in the calculation,
and simply do assigned-addresses/total-addresses. This would have a bias
towards under-representing pool utilization. As this has a potential for
major issues, we decided not to decrease assigned addresses immediately
after receiving Decline, but to do it later when we recover the address
back to the available pool.
9.12. Statistics in the DHCPv6 Server
Note
This section describes DHCPv6-specific statistics. For a general overview
and usage of statistics, see Chapter 15, Statistics.
The DHCPv6 server supports the following statistics:
Table 9.4. DHCPv6 Statistics
+----------------------------------------------------------------------------+
| Statistic |Data Type|Description |
|---------------------------------------+---------+--------------------------|
| | |Number of DHCPv6 packets |
| | |received. This includes |
| pkt6-received | integer |all packets: valid, bogus,|
| | |corrupted, rejected etc. |
| | |This statistic is expected|
| | |to grow rapidly. |
|---------------------------------------+---------+--------------------------|
| | |Number of incoming packets|
| | |that were dropped. The |
| | |exact reason for dropping |
| | |packets is logged, but the|
| | |most common reasons may |
| | |be: an unacceptable or not|
| pkt6-receive-drop | integer |supported packet type, |
| | |direct responses are |
| | |forbidden, the server-id |
| | |sent by the client does |
| | |not match the server's |
| | |server-id or the packet is|
| | |malformed. |
|---------------------------------------+---------+--------------------------|
| | |Number of incoming packets|
| | |that could not be parsed. |
| | |A non-zero value of this |
| | |statistic indicates that |
| | |the server received a |
| pkt6-parse-failed | integer |malformed or truncated |
| | |packet. This may indicate |
| | |problems in your network, |
| | |faulty clients, faulty |
| | |relay agents or a bug in |
| | |the server. |
|---------------------------------------+---------+--------------------------|
| | |Number of SOLICIT packets |
| | |received. This statistic |
| | |is expected to grow. Its |
| | |increase means that |
| pkt6-solicit-received | integer |clients that just booted |
| | |started their |
| | |configuration process and |
| | |their initial packets |
| | |reached your server. |
|---------------------------------------+---------+--------------------------|
| | |Number of ADVERTISE |
| | |packets received. |
| | |Advertise packets are sent|
| | |by the server and the |
| | |server is never expected |
| | |to receive them. A |
| | |non-zero value of this |
| pkt6-advertise-received | integer |statistic indicates an |
| | |error occurring in the |
| | |network. One likely cause |
| | |would be a misbehaving |
| | |relay agent that |
| | |incorrectly forwards |
| | |ADVERTISE messages towards|
| | |the server rather back to |
| | |the clients. |
|---------------------------------------+---------+--------------------------|
| | |Number of REQUEST packets |
| | |received. This statistic |
| | |is expected to grow. Its |
| | |increase means that |
| pkt6-request-received | integer |clients that just booted |
| | |received the server's |
| | |response (ADVERTISE), |
| | |accepted it and are now |
| | |requesting an address |
| | |(REQUEST). |
|---------------------------------------+---------+--------------------------|
| | |Number of REPLY packets |
| | |received. This statistic |
| | |is expected to remain zero|
| | |at all times, as REPLY |
| | |packets are sent by the |
| | |server and the server is |
| | |never expected to receive |
| pkt6-reply-received | integer |them. A non-zero value |
| | |indicates an error. One |
| | |likely cause would be a |
| | |misbehaving relay agent |
| | |that incorrectly forwards |
| | |REPLY messages towards the|
| | |server, rather back to the|
| | |clients. |
|---------------------------------------+---------+--------------------------|
| | |Number of RENEW packets |
| | |received. This statistic |
| | |is expected to grow. Its |
| pkt6-renew-received | integer |increase means that |
| | |clients received their |
| | |addresses and prefixes and|
| | |are trying to renew them. |
|---------------------------------------+---------+--------------------------|
| | |Number of REBIND packets |
| | |received. A non-zero value|
| | |indicates that clients |
| | |didn't receive responses |
| | |to their RENEW messages |
| | |(regular lease renewal |
| pkt6-rebind-received | integer |mechanism) and are |
| | |attempting to find any |
| | |server that is able to |
| | |take over their leases. It|
| | |may mean that some |
| | |server's REPLY messages |
| | |never reached the clients.|
|---------------------------------------+---------+--------------------------|
| | |Number of RELEASE packets |
| | |received. This statistic |
| | |is expected to grow when a|
| | |device is being shut down |
| | |in the network. It |
| | |indicates that the address|
| | |or prefix assigned is |
| pkt6-release-received | integer |reported as no longer |
| | |needed. Note that many |
| | |devices, especially |
| | |wireless, do not send |
| | |RELEASE packets either |
| | |because of design choice |
| | |or due to the client |
| | |moving out of range. |
|---------------------------------------+---------+--------------------------|
| | |Number of DECLINE packets |
| | |received. This statistic |
| | |is expected to remain |
| | |close to zero. Its |
| | |increase means that a |
| | |client leased an address, |
| | |but discovered that the |
| pkt6-decline-received | integer |address is currently used |
| | |by an unknown device in |
| | |your network. If this |
| | |statistic is growing, it |
| | |may indicate a |
| | |misconfigured server or |
| | |devices that have |
| | |statically assigned |
| | |conflicting addresses. |
|---------------------------------------+---------+--------------------------|
| | |Number of |
| | |INFORMATION-REQUEST |
| | |packets received. This |
| | |statistic is expected to |
| | |grow if there are devices |
| | |that are using stateless |
| pkt6-infrequest-received | integer |DHCPv6. |
| | |INFORMATION-REQUEST |
| | |messages are used by |
| | |clients that request |
| | |stateless configuration, |
| | |i.e. options and |
| | |parameters other than |
| | |addresses or prefixes. |
|---------------------------------------+---------+--------------------------|
| | |Number of DHCPv4-QUERY |
| | |packets received. This |
| | |statistic is expected to |
| | |grow if there are devices |
| | |that are using |
| pkt6-dhcpv4-query-received | integer |DHCPv4-over-DHCPv6. |
| | |DHCPv4-QUERY messages are |
| | |used by DHCPv4 clients on |
| | |an IPv6 only line which |
| | |encapsulates the requests |
| | |over DHCPv6. |
|---------------------------------------+---------+--------------------------|
| | |Number of DHCPv4-RESPONSE |
| | |packets received. This |
| | |statistic is expected to |
| | |remain zero at all times, |
| | |as DHCPv4-RESPONSE packets|
| | |are sent by the server and|
| | |the server is never |
| pkt6-dhcpv4-response-received | integer |expected to receive them. |
| | |A non-zero value indicates|
| | |an error. One likely cause|
| | |would be a misbehaving |
| | |relay agent that |
| | |incorrectly forwards |
| | |DHCPv4-RESPONSE message |
| | |towards the server rather |
| | |back to the clients. |
|---------------------------------------+---------+--------------------------|
| | |Number of packets received|
| | |of an unknown type. A |
| | |non-zero value of this |
| | |statistic indicates that |
| pkt6-unknown-received | integer |the server received a |
| | |packet that it wasn't able|
| | |to recognize: either it |
| | |had an unsupported type or|
| | |was possibly malformed. |
|---------------------------------------+---------+--------------------------|
| | |Number of DHCPv6 packets |
| | |sent. This statistic is |
| | |expected to grow every |
| | |time the server transmits |
| | |a packet. In general, it |
| | |should roughly match |
| | |pkt6-received, as most |
| pkt6-sent | integer |incoming packets cause the|
| | |server to respond. There |
| | |are exceptions (e.g. |
| | |server receiving a REQUEST|
| | |with server-id matching |
| | |other server), so do not |
| | |worry, if it is lesser |
| | |than pkt6-received. |
|---------------------------------------+---------+--------------------------|
| | |Number of ADVERTISE |
| | |packets sent. This |
| | |statistic is expected to |
| | |grow in most cases after a|
| | |SOLICIT is processed. |
| pkt6-advertise-sent | integer |There are certain |
| | |uncommon, but valid cases |
| | |where incoming SOLICIT is |
| | |dropped, but in general |
| | |this statistic is expected|
| | |to be close to |
| | |pkt6-solicit-received. |
|---------------------------------------+---------+--------------------------|
| | |Number of REPLY packets |
| | |sent. This statistic is |
| | |expected to grow in most |
| | |cases after a SOLICIT |
| | |(with rapid-commit), |
| pkt6-reply-sent | integer |REQUEST, RENEW, REBIND, |
| | |RELEASE, DECLINE or |
| | |INFORMATION-REQUEST is |
| | |processed. There are |
| | |certain cases where there |
| | |is no response. |
|---------------------------------------+---------+--------------------------|
| | |Number of DHCPv4-RESPONSE |
| | |packets sent. This |
| | |statistic is expected to |
| pkt6-dhcpv4-response-sent | integer |grow in most cases after a|
| | |DHCPv4-QUERY is processed.|
| | |There are certain cases |
| | |where there is no |
| | |response. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |total number of NA |
| | |addresses available for |
| | |DHCPv6 management for a |
| | |given subnet. In other |
| | |words, this is the sum of |
| | |all addresses in all |
| | |configured pools. This |
| | |statistic changes only |
| | |during configuration |
| subnet[id].total-nas | integer |changes. Note that it does|
| | |not take into account any |
| | |addresses that may be |
| | |reserved due to host |
| | |reservation. The id is the|
| | |subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately and is reset |
| | |during a reconfiguration |
| | |event. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of NA addresses in |
| | |a given subnet that are |
| | |assigned. This statistic |
| | |increases every time a new|
| | |lease is allocated (as a |
| | |result of receiving a |
| | |REQUEST message) and is |
| subnet[id].assigned-nas | integer |decreased every time a |
| | |lease is released (a |
| | |RELEASE message is |
| | |received) or expires. The |
| | |id is the subnet-id of a |
| | |given subnet. This |
| | |statistic is exposed for |
| | |each subnet separately and|
| | |is reset during a |
| | |reconfiguration event. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |total number of PD |
| | |prefixes available for |
| | |DHCPv6 management for a |
| | |given subnet. In other |
| | |words, this is the sum of |
| | |all prefixes in all |
| | |configured pools. This |
| | |statistic changes only |
| | |during configuration |
| subnet[id].total-pds | integer |changes. Note it does not |
| | |take into account any |
| | |prefixes that may be |
| | |reserved due to host |
| | |reservation. The id is the|
| | |subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately and is reset |
| | |during a reconfiguration |
| | |event. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of PD prefixes in a|
| | |given subnet that are |
| | |assigned. This statistic |
| | |increases every time a new|
| | |lease is allocated (as a |
| | |result of receiving a |
| | |REQUEST message) and is |
| subnet[id].assigned-pds | integer |decreased every time a |
| | |lease is released (a |
| | |RELEASE message is |
| | |received) or expires. The |
| | |id is the subnet-id of a |
| | |given subnet. This |
| | |statistic is exposed for |
| | |each subnet separately and|
| | |is reset during a |
| | |reconfiguration event. |
|---------------------------------------+---------+--------------------------|
| | |This statistic is the |
| | |number of expired leases |
| | |that have been reclaimed |
| | |since server startup. It |
| reclaimed-leases | integer |is incremented each time |
| | |an expired lease is |
| | |reclaimed (it counts both |
| | |NA and PD reclamations) |
| | |and is reset when the |
| | |server is reconfigured. |
|---------------------------------------+---------+--------------------------|
| | |This statistic is the |
| | |number of expired leases |
| | |associated with a given |
| | |subnet ("id" is the |
| | |subnet-id) that have been |
| | |reclaimed since server |
| subnet[id].reclaimed-leases | integer |startup. It is incremented|
| | |each time an expired lease|
| | |is reclaimed (it counts |
| | |both NA and PD |
| | |reclamations) and is reset|
| | |when the server is |
| | |reconfigured. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of IPv6 addresses |
| | |that are currently |
| | |declined and so counts the|
| | |number of leases currently|
| | |unavailable. Once a lease |
| | |is recovered, this |
| | |statistic will be |
| | |decreased. Ideally, this |
| declined-addresses | integer |statistic should be zero. |
| | |If this statistic is |
| | |non-zero (or worse, |
| | |increasing), the network |
| | |administrator should |
| | |investigate if there is a |
| | |misbehaving device in the |
| | |network. This is a global |
| | |statistic that covers all |
| | |subnets. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of IPv6 addresses |
| | |that are currently |
| | |declined in a given |
| | |subnet. This statistic |
| | |counts the number of |
| | |leases currently |
| | |unavailable. Once a lease |
| | |is recovered, this |
| | |statistic will be |
| | |decreased. Ideally, this |
| subnet[id].declined-addresses | integer |statistic should be zero. |
| | |If this statistic is |
| | |non-zero (or worse, |
| | |increasing), a network |
| | |administrator should |
| | |investigate if there is a |
| | |misbehaving device in the |
| | |network. The id is the |
| | |subnet-id of a given |
| | |subnet. This statistic is |
| | |exposed for each subnet |
| | |separately. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of IPv6 addresses |
| | |that were declined, but |
| | |have now been recovered. |
| | |Unlike declined-addresses,|
| | |this statistic never |
| reclaimed-declined-addresses | integer |decreases. It can be used |
| | |as a long term indicator |
| | |of how many actual valid |
| | |Declines were processed |
| | |and recovered from. This |
| | |is a global statistic that|
| | |covers all subnets. |
|---------------------------------------+---------+--------------------------|
| | |This statistic shows the |
| | |number of IPv6 addresses |
| | |that were declined, but |
| | |have now been recovered. |
| | |Unlike declined-addresses,|
| | |this statistic never |
| | |decreases. It can be used |
|subnet[id].reclaimed-declined-addresses| integer |as a long term indicator |
| | |of how many actual valid |
| | |Declines were processed |
| | |and recovered from. The id|
| | |is the subnet-id of a |
| | |given subnet. This |
| | |statistic is exposed for |
| | |each subnet separately. |
+----------------------------------------------------------------------------+
9.13. Management API for the DHCPv6 Server
The management API allows the issuing of specific management commands,
such as statistics retrieval, reconfiguration or shutdown. For more
details, see Chapter 16, Management API. Currently the only supported
communication channel type is UNIX stream socket. By default there are no
sockets open. To instruct Kea to open a socket, the following entry in the
configuration file can be used:
"Dhcp6": {
"control-socket": {
"socket-type": "unix",
"socket-name": "/path/to/the/unix/socket"
},
"subnet6": [
...
],
...
}
The length of the path specified by the socket-name parameter is
restricted by the maximum length for the unix socket name on your
operating system, i.e. the size of the sun_path field in the sockaddr_un
structure, decreased by 1. This value varies on different operating
systems between 91 and 107 characters. Typical values are 107 on Linux and
103 on FreeBSD.
Communication over control channel is conducted using JSON structures. See
the Control Channel section in the Kea Developer's Guide for more details.
The DHCPv6 server supports the following operational commands:
* build-report
* config-get
* config-reload
* config-set
* config-test
* config-write
* dhcp-disable
* dhcp-enable
* leases-reclaim
* list-commands
* shutdown
* version-get
as described in Section 16.3, "Commands Supported by Both the DHCPv4 and
DHCPv6 Servers". In addition, it supports the following statistics related
commands:
* statistic-get
* statistic-reset
* statistic-remove
* statistic-get-all
* statistic-reset-all
* statistic-remove-all
as described here Section 15.3, "Commands for Manipulating Statistics".
9.14. User contexts in IPv6
Kea allows loading hook libraries that sometimes could benefit from
additional parameters. If such a parameter is specific to the whole
library, it is typically defined as a parameter for the hook library.
However, sometimes there is a need to specify parameters that are
different for each pool.
User contexts can store arbitrary data as long as it is valid JSON syntax
and its top level element is a map (i.e. the data must be enclosed in
curly brackets). Some hook libraries may expect specific formatting,
though. Please consult specific hook library documentation for details.
User contexts can be specified on either global scope, shared network,
subnet, pool, client class, option data or definition level, and host
reservation. One other useful usage is the ability to store comments or
descriptions.
Let's consider a lightweight 4over6 deployment as an example. It is an
IPv6 transition technology that allows mapping IPv6 prefix into full or
parts of IPv4 addresses. In DHCP context, these are certain parameters
that are supposed to be delivered to clients in form of additional
options. Values of those options are correlated to delegated prefixes, so
it is reasonable to keep those parameters together with the PD pool. On
the other hand, lightweight 4over6 is not a commonly used feature, so it
is not a part of the base Kea code. The solution to this problem is to use
user context. For each PD pool that is expected to be used for lightweight
4over6, user context with extra parameters is defined. Those extra
parameters will be used by hook library that would be loaded only when
dynamic calculation of the lightweight 4over6 option is actually needed.
An example configuration looks as follows:
"Dhcp6": {
"subnet6": [ {
"pd-pools": [
{
"prefix": "2001:db8::",
"prefix-len": 56,
"delegated-len": 64,
// This is a pool specific context.
"user-context": {
"threshold-percent": 85,
"v4-network": "192.168.0.0/16",
"v4-overflow": "10.0.0.0/16",
"lw4over6-sharing-ratio": 64,
"lw4over6-v4-pool": "192.0.2.0/24",
"lw4over6-sysports-exclude": true,
"lw4over6-bind-prefix-len": 56
}
} ],
"subnet": "2001:db8::/32",
// This is a subnet specific context. You can put any type of
// information here as long as it is a valid JSON.
"user-context": {
"comment": "Those v4-v6 migration technologies are tricky.",
"experimental": true,
"billing-department": 42,
"contact-points": [ "Alice", "Bob" ]
}
} ],
...
}
Kea does not interpret or use the content of the user context: it just
stores it, making it available to the hook libraries. It is up to each
hook library to extract the information and make use of it. The parser
translates a "comment" entry into a user-context with the entry, this
allows to attach a comment inside the configuration itself.
For more background information, see Section 14.5, "User contexts".
9.15. Supported DHCPv6 Standards
The following standards are currently supported:
* Dynamic Host Configuration Protocol for IPv6, RFC 3315: Supported
messages are SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND,
INFORMATION-REQUEST, CONFIRM and REPLY.
* IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP)
version 6, RFC 3633: Supported options are IA_PD and IA_PREFIX. Also
supported is the status code NoPrefixAvail.
* DNS Configuration options for Dynamic Host Configuration Protocol for
IPv6 (DHCPv6), RFC 3646: Supported option is DNS_SERVERS.
* The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent
Remote-ID Option, RFC 4649: REMOTE-ID option is supported.
* The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully
Qualified Domain Name (FQDN) Option, RFC 4704: Supported option is
CLIENT_FQDN.
* Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for
Dual-Stack Lite, RFC 6334: the AFTR-Name DHCPv6 Option is supported.
* Relay-Supplied DHCP Options, RFC 6422: Full functionality is
supported: OPTION_RSOO, ability of the server to echo back the
options, checks whether an option is RSOO-enabled, ability to mark
additional options as RSOO-enabled.
* Prefix Exclude Option for DHCPv6-based Prefix Delegation, RFC 6603:
Prefix Exclude option is supported.
* Client Link-Layer Address Option in DHCPv6, RFC 6939: Supported option
is client link-layer address option.
* Issues and Recommendations with Multiple Stateful DHCPv6 Options, RFC
7550: All recommendations related to the DHCPv6 server operation are
supported.
* DHCPv6 Options for Configuration of Softwire Address and Port-Mapped
Clients, RFC 7598: All options specified in this specification are
supported by the DHCPv6 server.
9.16. DHCPv6 Server Limitations
These are the current limitations of the DHCPv6 server software. Most of
them are reflections of the early stage of development and should be
treated as "not implemented yet", rather than actual limitations.
* The server will allocate, renew or rebind a maximum of one lease for a
particular IA option (IA_NA or IA_PD) sent by a client. RFC 3315 and
RFC 3633 allow for multiple addresses or prefixes to be allocated for
a single IA.
* Temporary addresses are not supported.
* Client reconfiguration (RECONFIGURE) is not yet supported.
9.17. Kea DHCPv6 server examples
A collection of simple to use examples for DHCPv6 component of Kea is
available with the sources. It is located in doc/examples/kea6 directory.
At the time of writing this text there were 18 examples, but the number is
growing slowly with each release.
Chapter 10. Lease Expiration in DHCPv4 and DHCPv6
Table of Contents
10.1. Lease Reclamation
10.2. Configuring Lease Reclamation
10.3. Configuring Lease Affinity
10.4. Default Configuration Values for Leases Reclamation
10.5. Reclaiming Expired Leases with Command
The primary role of the DHCP server is to assign addresses and/or delegate
prefixes to DHCP clients. These addresses and prefixes are often referred
to as "leases". Leases are typically assigned to clients for a finite
amount of time, known as the "valid lifetime". DHCP clients who wish to
continue using their assigned leases, will periodically renew them by
sending the appropriate message to the DHCP server. The DHCP server
records the time when these leases are renewed and calculates new
expiration times for them.
If the client does not renew a lease before its valid lifetime elapses,
the lease is considered expired. There are many situations when the client
may cease lease renewals. A common scenario is when the machine running
the client shuts down for an extended period of time.
The process through which the DHCP server makes expired leases available
for reassignment is referred to as "lease reclamation" and expired leases
returned to availability through this process are referred to as
"reclaimed". The DHCP server attempts to reclaim an expired lease as soon
as it detects that it has expired. One way in which the server detects
expiration occurs when it is trying to allocate a lease to a client and
finds this lease already present in the database but expired. Another way
is by periodically querying the lease database for them. Regardless of how
an expired lease is detected, before it may assigned to a client, it must
be reclaimed.
This chapter explains how to configure the server to periodically query
for the expired leases and how to minimize the impact of the periodic
lease reclamation process on the server's responsiveness. Finally, it
explains "lease affinity", which provides the means to assign the same
lease to a returning client after its lease has expired.
Although, all configuration examples in this section are provided for the
DHCPv4 server, the same parameters may be used for the DHCPv6 server
configuration.
10.1. Lease Reclamation
Lease reclamation is the process through which an expired lease becomes
available for assignment to the same or different client. This process
involves the following steps for each reclaimed lease:
* Invoke callouts for the lease4_expire or lease6_expire hook points if
hook libraries supporting those callouts are currently loaded.
* Update DNS, i.e. remove any DNS entries associated with the expired
lease.
* Update lease information in the lease database to indicate that the
lease is now available for re-assignment.
* Update counters on the server, which includes increasing the number of
reclaimed leases and decreasing the number of assigned addresses or
delegated prefixes.
Please refer to Chapter 11, The DHCP-DDNS Server to see how to configure
DNS updates in Kea, and to Chapter 14, Hooks Libraries for information
about using hooks libraries.
10.2. Configuring Lease Reclamation
Kea can be configured to periodically detect and reclaim expired leases.
During this process the lease entries in the database are modified or
removed. While this is happening the server will not process incoming DHCP
messages to avoid issues with concurrent access to database information.
As a result, the server will be unresponsive while lease reclamation is
performed and DHCP queries will accumulate; responses will be sent once
the leases reclamation cycle is complete.
In deployments where response time is critical, administrators may wish to
minimize the interruptions in service caused by lease reclamation. Toward
this end, Kea provides configuration parameters to control: the frequency
of lease reclamation cycles, the maximum number of leases processed in a
single reclamation cycle, and the maximum amount of time a single
reclamation cycle is allowed to run before being interrupted. The
following examples demonstrate how these parameters can be used:
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 5,
"max-reclaim-leases": 0,
"max-reclaim-time": 0,
"flush-reclaimed-timer-wait-time": 0,
},
...
}
The first parameter is expressed in seconds and specifies an interval
between the two consecutive lease reclamation cycles. This is explained by
the following diagram.
| c1 | | c2 | |c3| | c4 |
|<---->|<---------->|<-->|<---------->|<>|<---------->|<-->|
---------------------------------------------------------------->
| | 5s | | 5s | | 5s | | time
This diagram shows four lease reclamation cycles (c1 through c4) of
variable duration. Note that the duration of the reclamation cycle depends
on the number of expired leases detected and processed in the particular
cycle. This duration is also usually significantly shorter than the
interval between the cycles.
According to the reclaim-timer-wait-time the server keeps fixed intervals
of five seconds between the end of one cycle and the start of the next
cycle. This guarantees the presence of 5s long periods during which the
server remains responsive to DHCP queries and does not perform lease
reclamation. The max-reclaim-leases and max-reclaim-time are set to 0,
which sets no restriction on the maximum number of leases reclaimed in the
particular cycle, or on the maximum duration of each cycle.
In deployments with high lease pool utilization, relatively short valid
lifetimes, and frequently disconnecting clients which allow leases to
expire, the number of expired leases requiring reclamation at any given
time may rise significantly. In this case it is often desirable to apply
restrictions on the maximum duration of a reclamation cycle or the maximum
number of leases reclaimed in a cycle. The following configuration
demonstrates how this can be done:
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 3,
"max-reclaim-leases": 100,
"max-reclaim-time": 50,
"unwarned-reclaim-cycles": 10,
},
...
}
The max-reclaim-leases parameter limits the number of leases reclaimed in
a single cycle to 100. The max-reclaim-time limits the maximum duration of
each cycle to 50ms. The lease reclamation cycle will be interrupted if
either of these limitations is reached. The reclamation of all unreclaimed
leases will be attempted in subsequent cycles.
The following diagram illustrates the behavior of the system in the
presence of many expired leases, when the limits are applied for the
reclamation cycles.
| c1 | | c2 | | c3 | | c4 |
|<-->|<-------------->|<-->|<-------------->|<-->|<-------------->|<-->|<--
------------------------------------------------------------------------------>
|50ms| 3s |50ms| 3s |50ms| 3s |50ms| time
The diagram demonstrates the case when each reclamation cycle would take
more than 50ms, and thus is interrupted according to the value of the
max-reclaim-time. This results in equal durations of all reclamation
cycles over time. Note that in this example the limitation of maximum 100
leases is not reached. This may be the case when database transactions are
slow or callouts in the hook libraries attached to the server are slow.
Regardless, the choosing values for either the maximum number of leases or
a maximum cycle time strongly depends on the particular deployment, lease
database backend being used, and any hooks libraries etc. Administrators
may need to experiment to tune the system to suit the dynamics of their
deployment.
It is important to realize that with the use of these limits, there is a
risk that expired leases will accumulate faster than the server can
reclaim them. This should not be the problem if the server is dealing with
a temporary burst of expirations, because it should be able to eventually
deal with them over time. However, if leases expire at a high rate for a
longer period of time, the unreclaimed leases will pile up in the
database. In order to notify the administrator that the current
configuration does not satisfy the needs for reclamation of expired
leases, the server issues a warning message in the log if it was unable to
reclaim all leases within the last couple of reclamation cycles. The
number of cycles after which such warning is issued is specified with the
unwarned-reclaim-cycles configuration parameter.
Setting the reclaim-timer-wait-time to 0 disables periodic reclamation of
the expired leases.
10.3. Configuring Lease Affinity
Suppose that a laptop goes to a sleep mode after a period of user
inactivity. While the laptop is in sleep mode, its DHCP client will not
renew leases obtained from the server and these leases will eventually
expire. When the laptop wakes up, it is often desirable for it to continue
using its previous assigned IP addresses. In order to facilitate this, the
server needs to correlate returning clients with their expired leases When
the client returns, the server will first check for those leases and
re-assign them if they have not been assigned to another client. The
ability of the server to re-assign the same lease to a returning client is
referred to as "lease affinity".
When lease affinity is enabled, the server will still reclaim leases
according to the parameters described in Section 10.2, "Configuring Lease
Reclamation", but the reclaimed leases will be held in the database
(rather than removed) for the specified amount of time. When the client
returns, the server will first check if there are any reclaimed leases
associated with this client and re-assign them if possible. However, it is
important to note that any reclaimed lease may be assigned to another
client if that client specifically asks for it. Therefore, the lease
affinity does not guarantee that the reclaimed lease will be available for
the client who used it before; it merely increases the chances for the
client to be assigned the same lease. If the lease pool is small (this
mostly applies to DHCPv4 for which address space is small), there is an
increased likelihood that the expired lease will be assigned to another
client.
Consider the following configuration:
"Dhcp4": {
...
"expired-leases-processing": {
"reclaim-timer-wait-time": 3,
"hold-reclaimed-time": 1800,
"flush-reclaimed-timer-wait-time": 5
},
...
}
The hold-reclaim-time specifies how many seconds after an expiration a
reclaimed lease should be held in the database for re-assignment to the
same client. In the example given above, reclaimed leases will be held for
30 minutes (1800s) after their expiration. During this time, the server
will likely be able to re-assign the same lease to the returning client,
unless another client requests this lease and the server assigns it.
The server must periodically remove reclaimed leases for which the time
indicated by hold-reclaim-time has elapsed. The
flush-reclaimed-timer-wait-time controls how often the server removes such
leases. In the example provided above, the server will initiate removal of
such leases 5 seconds after the previous removal attempt was completed.
Setting this value to 0 disables lease affinity, in which case leases will
be removed from the lease database when they are reclaimed. If lease
affinity is enabled, it is recommended that hold-reclaim-time be set to a
value significantly higher than the reclaim-timer-wait-time, as timely
removal of expired-reclaimed leases is less critical while the removal
process may impact server responsiveness.
10.4. Default Configuration Values for Leases Reclamation
The following list presents all configuration parameters pertaining to
processing expired leases with their default values:
* reclaim-timer-wait-time = 10 [seconds]
* flush-reclaimed-timer-wait-time = 25 [seconds]
* hold-reclaimed-time = 3600 [seconds]
* max-reclaim-leases = 100
* max-reclaim-time = 250 [milliseconds]
* unwarned-reclaim-cycles = 5
The default value for any parameter is used when this parameter not
explicitly specified in the configuration. Also, the
expired-leases-processing map may be omitted entirely in the
configuration, in which case the default values are used for all
parameters listed above.
10.5. Reclaiming Expired Leases with Command
The leases-reclaim command can be used to trigger leases reclamation at
any time. Please consult the Section 16.3.6, "leases-reclaim" for the
details about using this command.
Chapter 11. The DHCP-DDNS Server
Table of Contents
11.1. Overview
11.1.1. DNS Server selection
11.1.2. Conflict Resolution
11.1.3. Dual Stack Environments
11.2. Starting and Stopping the DHCP-DDNS Server
11.3. Configuring the DHCP-DDNS Server
11.3.1. Global Server Parameters
11.3.2. TSIG Key List
11.3.3. Forward DDNS
11.3.4. Reverse DDNS
11.3.5. User context in DDNS
11.3.6. Example DHCP-DDNS Server Configuration
11.4. DHCP-DDNS Server Limitations
11.1. Overview
The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the
client side of the DDNS protocol (defined in RFC 2136) on behalf of the
DHCPv4 and DHCPv6 servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP
servers construct DDNS update requests, known as NameChangeRequests
(NCRs), based upon DHCP lease change events and then post these to D2. D2
attempts to match each such request to the appropriate DNS server(s) and
carry out the necessary conversation with those servers to update the DNS
data.
11.1.1. DNS Server selection
In order to match a request to the appropriate DNS servers, D2 must have a
catalog of servers from which to select. In fact, D2 has two such
catalogs, one for forward DNS and one for reverse DNS; these catalogs are
referred to as DDNS Domain Lists. Each list consists of one or more named
DDNS Domains. Further, each DDNS Domain has a list of one or more DNS
servers that publish the DNS data for that domain.
When conducting forward domain matching, D2 will compare the FQDN in the
request against the name of each forward DDNS Domain. The domain whose
name matches the longest portion of the FQDN is considered the best match.
For example, if the FQDN is "myhost.sample.example.com.", and there are
two forward domains in the catalog: "sample.example.com." and
"example.com.", the former is regarded as the best match. In some cases,
it may not be possible to find a suitable match. Given the same two
forward domains there would be no match for the FQDN, "bogus.net", so the
request would be rejected. Finally, if there are no forward DDNS Domains
defined, D2 will simply disregard the forward update portion of requests.
When conducting reverse domain matching, D2 constructs a reverse FQDN from
the lease address in the request and compare that against the name of each
reverse DDNS Domain. Again, the domain whose name matches the longest
portion of the FQDN is considered the best match. For instance, if the
lease address is "172.16.1.40" and there are two reverse domains in the
catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the former is
the best match. As with forward matching, it is possible to not find a
suitable match. Given the same two domains, there would be no match for
the lease address, "192.168.1.50", and the request would be rejected.
Finally, if there are no reverse DDNS Domains defined, D2 will simply
disregard the reverse update portion of requests.
11.1.2. Conflict Resolution
D2 implements the conflict resolution strategy prescribed by RFC 4703.
Conflict resolution is intended to prevent different clients from mapping
to the same FQDN at the same time. To make this possible, the RFC requires
that forward DNS entries for a given FQDN must be accompanied by a DHCID
resource record (RR). This record contains a client identifier that
uniquely identifies the client to whom the name belongs. Furthermore, any
DNS updater who wishes to update or remove existing forward entries for an
FQDN may only do so if their client matches that of the DHCID RR.
In other words, the DHCID RR maps an FQDN to the client to whom it belongs
and thereafter only changes to that mapping should only be done by or at
the behest of that client.
Currently, conflict detection is always performed. Future releases may
offer alternative behavior.
11.1.3. Dual Stack Environments
RFC 4703, sec. 5.2, describes issues that may arise with dual stack
clients. These are clients that wish to have have both IPv4 and IPv6
mappings for the same FQDN. In order for this work properly, such clients
are required to embed ther IPv6 DUID within their IPv4 client identifier
option as described in RFC 4703. In this way, DNS upates for both IPv4 and
IPv6 can be managed under the same DHCID RR. Support for this does not yet
exist in Kea but is called for in the ticket,
http://kea.isc.org/ticket/4519, which we hope to include in a future
release.
11.2. Starting and Stopping the DHCP-DDNS Server
kea-dhcp-ddns is the Kea DHCP-DDNS server and, due to the nature of DDNS,
it is run alongside either the DHCPv4 or DHCPv6 components (or both). Like
other parts of Kea, it is a separate binary that can be run on its own or
through keactrl (see Chapter 6, Managing Kea with keactrl). In normal
operation, controlling kea-dhcp-ddns with keactrl is recommended. However,
it is also possible to run the DHCP-DDNS server directly. It accepts the
following command-line switches:
* -c file - specifies the configuration file. This is the only mandatory
switch.
* -d - specifies whether the server logging should be switched to
debug/verbose mode. In verbose mode, the logging severity and
debuglevel specified in the configuration file are ignored and "debug"
severity and the maximum debuglevel (99) are assumed. The flag is
convenient, for temporarily switching the server into maximum
verbosity, e.g. when debugging.
* -v - prints out Kea version and exits.
* -W - prints out the Kea configuration report and exits. The report is
a copy of the config.report file produced by ./configure: it is
embedded in the executable binary.
* -t file specifies the configuration file to be tested. Kea-dhcp-ddns
will attempt to load it, and will conduct sanity checks. Note that
certain checks are possible only while running the actual server. The
actual status is reported with exit code (0 = configuration looks ok,
1 = error encountered). Kea will print out log messages to standard
output and error to standard error when testing configuration.
The config.report may also be accessed more directly. The following
command may be used to extract this information. The binary path may be
found in the install directory or in the .libs subdirectory in the source
tree. For example kea/src/bin/d2/.libs/kea-dhcp-ddns.
strings path/kea-dhcp-ddns | sed -n 's/;;;; //p'
Upon start up the module will load its configuration and begin listening
for NCRs based on that configuration.
During startup the server will attempt to create a PID file of the form:
[localstatedir]/[conf name].kea-dhcp-ddns.pid where:
* localstatedir: The value as passed into the build configure script. It
defaults to "/usr/local/var". Note that this value may be overridden
at run time by setting the environment variable KEA_PIDFILE_DIR. This
is intended primarily for testing purposes.
* conf name: The configuration file name used to start the server, minus
all preceding path and file extension. For example, given a pathname
of "/usr/local/etc/kea/myconf.txt", the portion used would be
"myconf".
If the file already exists and contains the PID of a live process, the
server will issue a DHCP_DDNS_ALREADY_RUNNING log message and exit. It is
possible, though unlikely, that the file is a remnant of a system crash
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
11.3. Configuring the DHCP-DDNS Server
Before starting kea-dhcp-ddns module for the first time, a configuration
file needs to be created. The following default configuration is a
template that can be customized to your requirements.
"DhcpDdns": {
"ip-address": "127.0.0.1",
"port": 53001,
"dns-server-timeout": 100,
"ncr-protocol": "UDP",
"ncr-format": "JSON",
"tsig-keys": [ ],
"forward-ddns": {
"ddns-domains": [ ]
},
"reverse-ddns": {
"ddns-domains": [ ]
}
}
The configuration can be divided as follows, each of which is described in
its own section:
* Global Server Parameters - values which control connectivity and
global server behavior
* TSIG Key Info - defines the TSIG keys used for secure traffic with DNS
servers
* Forward DDNS - defines the catalog of Forward DDNS Domains
* Reverse DDNS - defines the catalog of Forward DDNS Domains
11.3.1. Global Server Parameters
* ip-address - IP address on which D2 listens for requests. The default
is the local loopback interface at address 127.0.0.1. You may specify
either an IPv4 or IPv6 address.
* port - Port on which D2 listens for requests. The default value is
53001.
* dns-server-timeout - The maximum amount of time in milliseconds, that
D2 will wait for a response from a DNS server to a single DNS update
message.
* ncr-protocol - Socket protocol to use when sending requests to D2.
Currently only UDP is supported. TCP may be available in a future
release.
* ncr-format - Packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be
available in future releases.
D2 must listen for change requests on a known address and port. By default
it listens at 127.0.0.1 on port 53001. The following example illustrates
how to change D2's global parameters so it will listen at 192.168.1.10
port 900:
"DhcpDdns": {
"ip-address": "192.168.1.10",
"port": 900,
...
}
}
Warning
It is possible for a malicious attacker to send bogus NameChangeRequests
to the DHCP-DDNS server. Addresses other than the IPv4 or IPv6 loopback
addresses (127.0.0.1 or ::1) should only be used for testing purposes, but
note that local users may still communicate with the DHCP-DDNS server. A
future version of Kea will implement authentication to guard against such
attacks.
Note
If the ip-address and port are changed, it will be necessary to change the
corresponding values in the DHCP servers' "dhcp-ddns" configuration
section.
11.3.2. TSIG Key List
A DDNS protocol exchange can be conducted with or without TSIG (defined in
RFC 2845). This configuration section allows the administrator to define
the set of TSIG keys that may be used in such exchanges.
To use TSIG when updating entries in a DNS Domain, a key must be defined
in the TSIG Key List and referenced by name in that domain's configuration
entry. When D2 matches a change request to a domain, it checks whether the
domain has a TSIG key associated with it. If so, D2 will use that key to
sign DNS update messages sent to and verify responses received from the
domain's DNS server(s). For each TSIG key required by the DNS servers that
D2 will be working with there must be a corresponding TSIG key in the TSIG
Key list.
As one might gather from the name, the tsig-key section of the D2
configuration lists the TSIG keys. Each entry describes a TSIG key used by
one or more DNS servers to authenticate requests and sign responses. Every
entry in the list has three parameters:
* name - a unique text label used to identify this key within the list.
This value is used to specify which key (if any) should be used when
updating a specific domain. So long as it is unique its content is
arbitrary, although for clarity and ease of maintenance it is
recommended that it match the name used on the DNS server(s). It
cannot be blank.
* algorithm - specifies which hashing algorithm should be used with this
key. This value must specify the same algorithm used for the key on
the DNS server(s). The supported algorithms are listed below:
* HMAC-MD5
* HMAC-SHA1
* HMAC-SHA224
* HMAC-SHA256
* HMAC-SHA384
* HMAC-SHA512
This value is not case sensitive.
* digest-bits - is used to specify the minimum truncated length in bits.
The default value 0 means truncation is forbidden, non-zero values
must be an integral number of octets, be greater than 80 and the half
of the full length. Note in BIND9 this parameter is appended after a
dash to the algorithm name.
* secret - is used to specify the shared secret key code for this key.
This value is case sensitive and must exactly match the value
specified on the DNS server(s). It is a base64-encoded text value.
As an example, suppose that a domain D2 will be updating is maintained by
a BIND9 DNS server which requires dynamic updates to be secured with TSIG.
Suppose further that the entry for the TSIG key in BIND9's named.conf file
looks like this:
:
key "key.four.example.com." {
algorithm hmac-sha224;
secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
};
:
By default, the TSIG Key list is empty:
"DhcpDdns": {
"tsig-keys": [ ],
...
}
We must extend the list with a new key:
"DhcpDdns": {
"tsig-keys": [
{
"name": "key.four.example.com.",
"algorithm": "HMAC-SHA224",
"secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
}
],
...
}
These steps would be repeated for each TSIG key needed. Note that the same
TSIG key can be used with more than one domain.
11.3.3. Forward DDNS
The Forward DDNS section is used to configure D2's forward update
behavior. Currently it contains a single parameter, the catalog of forward
DDNS Domains, which is a list of structures.
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [ ]
},
...
}
By default, this list is empty, which will cause the server to ignore the
forward update portions of requests.
11.3.3.1. Adding Forward DDNS Domains
A forward DDNS Domain maps a forward DNS zone to a set of DNS servers
which maintain the forward DNS data (i.e. name to address mapping) for
that zone. You will need one forward DDNS Domain for each zone you wish to
service. It may very well be that some or all of your zones are maintained
by the same servers. You will still need one DDNS Domain per zone.
Remember that matching a request to the appropriate server(s) is done by
zone and a DDNS Domain only defines a single zone.
This section describes how to add Forward DDNS Domains. Repeat these steps
for each Forward DDNS Domain desired. Each Forward DDNS Domain has the
following parameters:
* name - The fully qualified domain name (or zone) that this DDNS Domain
can update. This is value used to compare against the request FQDN
during forward matching. It must be unique within the catalog.
* key-name - If TSIG is used with this domain's servers, this value
should be the name of the key from within the TSIG Key List to use. If
the value is blank (the default), TSIG will not be used in DDNS
conversations with this domain's servers.
* dns-servers - A list of one or more DNS servers which can conduct the
server side of the DDNS protocol for this domain. The servers are used
in a first to last preference. In other words, when D2 begins to
process a request for this domain it will pick the first server in
this list and attempt to communicate with it. If that attempt fails,
it will move to next one in the list and so on until the it achieves
success or the list is exhausted.
To create a new forward DDNS Domain, one must add a new domain element and
set its parameters:
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [
{
"name": "other.example.com.",
"key-name": "",
"dns-servers": [
]
}
]
}
}
It is permissible to add a domain without any servers. If that domain
should be matched to a request, however, the request will fail. In order
to make the domain useful though, we must add at least one DNS server to
it.
11.3.3.1.1. Adding Forward DNS Servers
This section describes how to add DNS servers to a Forward DDNS Domain.
Repeat them for as many servers as desired for a each domain.
Forward DNS Server entries represent actual DNS servers which support the
server side of the DDNS protocol. Each Forward DNS Server has the
following parameters:
* hostname - The resolvable host name of the DNS server. This value is
not yet implemented.
* ip-address - The IP address at which the server listens for DDNS
requests. This may be either an IPv4 or an IPv6 address.
* port - The port on which the server listens for DDNS requests. It
defaults to the standard DNS service port of 53.
To create a new forward DNS Server, one must add a new server element to
the domain and fill in its parameters. If for example the service is
running at "172.88.99.10", then set it as follows:
"DhcpDdns": {
"forward-ddns": {
"ddns-domains": [
{
"name": "other.example.com.",
"key-name": "",
"dns-servers": [
{
"hostname": "",
"ip-address": "172.88.99.10",
"port": 53
}
]
}
]
}
}
Note
As stated earlier, "hostname" is not yet supported so, the parameter
"ip-address" must be set to the address of the DNS server.
11.3.4. Reverse DDNS
The Reverse DDNS section is used to configure D2's reverse update
behavior, and the concepts are the same as for the forward DDNS section.
Currently it contains a single parameter, the catalog of reverse DDNS
Domains, which is a list of structures.
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [ ]
}
...
}
By default, this list is empty, which will cause the server to ignore the
reverse update portions of requests.
11.3.4.1. Adding Reverse DDNS Domains
A reverse DDNS Domain maps a reverse DNS zone to a set of DNS servers
which maintain the reverse DNS data (address to name mapping) for that
zone. You will need one reverse DDNS Domain for each zone you wish to
service. It may very well be that some or all of your zones are maintained
by the same servers; even then, you will still need one DDNS Domain entry
for each zone. Remember that matching a request to the appropriate
server(s) is done by zone and a DDNS Domain only defines a single zone.
This section describes how to add Reverse DDNS Domains. Repeat these steps
for each Reverse DDNS Domain desired. Each Reverse DDNS Domain has the
following parameters:
* name - The fully qualified reverse zone that this DDNS Domain can
update. This is the value used during reverse matching which will
compare it with a reversed version of the request's lease address. The
zone name should follow the appropriate standards: for example, to to
support the IPv4 subnet 172.16.1, the name should be.
"1.16.172.in-addr.arpa.". Similarly, to support an IPv6 subnet of
2001:db8:1, the name should be "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
Whatever the name, it must be unique within the catalog.
* key-name - If TSIG should be used with this domain's servers, then
this value should be the name of that key from the TSIG Key List. If
the value is blank (the default), TSIG will not be used in DDNS
conversations with this domain's servers. Currently this value is not
used as TSIG has not been implemented.
* dns-servers - a list of one or more DNS servers which can conduct the
server side of the DDNS protocol for this domain. Currently the
servers are used in a first to last preference. In other words, when
D2 begins to process a request for this domain it will pick the first
server in this list and attempt to communicate with it. If that
attempt fails, it will move to next one in the list and so on until
the it achieves success or the list is exhausted.
To create a new reverse DDNS Domain, one must add a new domain element and
set its parameters. For example, to support subnet 2001:db8:1::, the
following configuration could be used:
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [
{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
]
}
]
}
}
It is permissible to add a domain without any servers. If that domain
should be matched to a request, however, the request will fail. In order
to make the domain useful though, we must add at least one DNS server to
it.
11.3.4.1.1. Adding Reverse DNS Servers
This section describes how to add DNS servers to a Reverse DDNS Domain.
Repeat them for as many servers as desired for each domain.
Reverse DNS Server entries represents a actual DNS servers which support
the server side of the DDNS protocol. Each Reverse DNS Server has the
following parameters:
* hostname - The resolvable host name of the DNS server. This value is
currently ignored.
* ip-address - The IP address at which the server listens for DDNS
requests.
* port - The port on which the server listens for DDNS requests. It
defaults to the standard DNS service port of 53.
To create a new reverse DNS Server, one must first add a new server
element to the domain and fill in its parameters. If for example the
service is running at "172.88.99.10", then set it as follows:
"DhcpDdns": {
"reverse-ddns": {
"ddns-domains": [
{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
{
"hostname": "",
"ip-address": "172.88.99.10",
"port": 53
}
]
}
]
}
}
Note
As stated earlier, "hostname" is not yet supported so, the parameter
"ip-address" must be set to the address of the DNS server.
11.3.5. User context in DDNS
Note
User contexts were designed for hook libraries which are not yet supported
for DHCP-DDNS server configuration.
User contexts can store arbitrary data as long as it is valid JSON syntax
and its top level element is a map (i.e. the data must be enclosed in
curly brackets).
User contexts can be specified on either global scope, ddns domain, dns
server, tsig key and loggers. One other useful usage is the ability to
store comments or descriptions: the parser translates a "comment" entry
into a user-context with the entry, this allows to attach a comment inside
the configuration itself.
11.3.6. Example DHCP-DDNS Server Configuration
This section provides an example DHCP-DDNS server configuration based on a
small example network. Let's suppose our example network has three
domains, each with their own subnet.
Table 11.1. Our example network
+------------------------------------------------------------------------+
| Domain | Subnet | Forward DNS Servers | Reverse DNS |
| | | | Servers |
|------------------+-----------------+---------------------+-------------|
| four.example.com | 192.0.2.0/24 | 172.16.1.5, | 172.16.1.5, |
| | | 172.16.2.5 | 172.16.2.5 |
|------------------+-----------------+---------------------+-------------|
| six.example.com | 2001:db8:1::/64 | 3001:1::50 | 3001:1::51 |
|------------------+-----------------+---------------------+-------------|
| example.com | 192.0.0.0/16 | 172.16.2.5 | 172.16.2.5 |
+------------------------------------------------------------------------+
We need to construct three forward DDNS Domains:
Table 11.2. Forward DDNS Domains Needed
+-------------------------------------------------+
| # | DDNS Domain Name | DNS Servers |
|----+-------------------+------------------------|
| 1. | four.example.com. | 172.16.1.5, 172.16.2.5 |
|----+-------------------+------------------------|
| 2. | six.example.com. | 3001:1::50 |
|----+-------------------+------------------------|
| 3. | example.com. | 172.16.2.5 |
+-------------------------------------------------+
As discussed earlier, FQDN to domain matching is based on the longest
match. The FQDN, "myhost.four.example.com.", will match the first domain
("four.example.com") while "admin.example.com." will match the third
domain ("example.com"). The FQDN, "other.example.net." will fail to match
any domain and would be rejected.
The following example configuration specified the Forward DDNS Domains.
"DhcpDdns": {
"comment": "example configuration: forward part",
"forward-ddns": {
"ddns-domains": [
{
"name": "four.example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.1.5" },
{ "ip-address": "172.16.2.5" }
]
},
{
"name": "six.example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "2001:db8::1" }
]
},
{
"name": "example.com.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.2.5" }
],
"user-context": { "backup": false }
},
]
}
}
Similarly, we need to construct the three reverse DDNS Domains:
Table 11.3. Reverse DDNS Domains Needed
+-----------------------------------------------------------------+
| # | DDNS Domain Name | DNS Servers |
|----+-----------------------------------+------------------------|
| 1. | 2.0.192.in-addr.arpa. | 172.16.1.5, 172.16.2.5 |
|----+-----------------------------------+------------------------|
| 2. | 1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa. | 3001:1::50 |
|----+-----------------------------------+------------------------|
| 3. | 0.182.in-addr.arpa. | 172.16.2.5 |
+-----------------------------------------------------------------+
An address of "192.0.2.150" will match the first domain, "2001:db8:1::10"
will match the second domain, and "192.0.50.77" the third domain.
These Reverse DDNS Domains are specified as follows:
"DhcpDdns": {
"comment": "example configuration: reverse part",
"reverse-ddns": {
"ddns-domains": [
{
"name": "2.0.192.in-addr.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.1.5" },
{ "ip-address": "172.16.2.5" }
]
}
{
"name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "2001:db8::1" }
]
}
{
"name": "0.192.in-addr.arpa.",
"key-name": "",
"dns-servers": [
{ "ip-address": "172.16.2.5" }
]
}
]
}
}
11.4. DHCP-DDNS Server Limitations
The following are the current limitations of the DHCP-DDNS Server.
* Requests received from the DHCP servers are placed in a queue until
they are processed. Currently all queued requests are lost when the
server shuts down.
Chapter 12. The LFC process
Table of Contents
12.1. Overview
12.2. Command Line Options
12.1. Overview
kea-lfc is a service process that removes redundant information from the
files used to provide persistent storage for the memfile data base
backend. This service is written to run as a stand alone process.
While kea-lfc can be started externally, there is usually no need to do
this. kea-lfc is run on a periodic basis by the Kea DHCP servers.
The process operates on a set of files, using them for input and output of
the lease entries and to indicate where it is in the process in case of an
interruption. Currently the caller must supply names for all of the files,
in the future this requirement may be relaxed with the process getting the
names from either the configuration file or from defaults.
12.2. Command Line Options
kea-lfc is run as follows:
kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file
The argument -4 or -6 selects the protocol version of the lease files.
The -c argument specifies the configuration file. This is required, but
not currently used by the process.
The -p argument specifies the PID file. When the kea-lfc process starts it
attempts to determine if another instance of the process is already
running by examining the pid file. If one is already running the new
process is terminated. If one isn't running it writes its pid into the pid
file.
The other filenames specify where the kea-lfc process should look for
input, write its output and use for bookkeeping.
* previous -- When kea-lfc starts this is the result of any previous run
of kea-lfc. When kea-lfc finishes it is the result of this run. If
kea-lfc is interrupted before completing, this file may not exist.
* input -- Before the DHCP server invokes kea-lfc it will move the
current lease file here and then call kea-lfc with this file.
* output -- The temporary file kea-lfc should use to write the leases.
Upon completion of writing this file, it will be moved to the finish
file (see below).
* finish -- Another temporary file kea-lfc uses for bookkeeping. When
kea-lfc completes writing the outputfile it moves it to this file
name. After kea-lfc finishes deleting the other files (previous and
input) it moves this file to previous lease file. By moving the files
in this fashion the kea-lfc and the DHCP server processes can
determine the correct file to use even if one of the processes was
interrupted before completing its task.
There are several additional arguments mostly for debugging purposes. -d
Sets the logging level to debug. -v and -V print out version stamps with
-V providing a longer form. -h prints out the usage string.
Chapter 13. Client Classification
Table of Contents
13.1. Client Classification Overview
13.2. Builtin Client Classes
13.3. Using Expressions In Classification
13.3.1. Logical operators
13.3.2. Substring
13.3.3. Concat
13.3.4. Ifelse
13.4. Configuring Classes
13.5. Using Static Host Reservations In Classification
13.6. Configuring Subnets With Class Information
13.7. Configuring Pools With Class Information
13.8. Using Classes
13.9. Classes and Hooks
13.10. Debugging Expressions
13.1. Client Classification Overview
In certain cases it is useful to differentiate between different types of
clients and treat them accordingly. Common reasons include:
* The clients represent different pieces of topology, e.g. a cable modem
is different to the clients behind that modem.
* The clients have different behavior, e.g. a smart phone behaves
differently to a laptop.
* The clients require different values for some options, e.g. a
docsis3.0 cable modem requires different settings to docsis2.0 cable
modem.
Conversely, different clients can be grouped into a client class to get a
common option.
An incoming packet can be associated with a client class in serveral ways:
* Implicitly, using a vendor class option or another builtin condition.
* Using an expression which evaluates to true.
* Using static host reservations, a shared network, a subnet, etc.
* Using a hook.
It is envisaged that client classification will be used for changing the
behavior of almost any part of the DHCP message processing. In the current
release of the software however, there are only five mechanisms that take
advantage of client classification: subnet selection, pool selection,
definition of DHCPv4 private (codes 224-254) and code 43 options,
assignment of different options and, for DHCPv4 cable modems, the setting
of specific options for use with the TFTP server address and the boot file
field.
The process of doing classification is conducted in several steps:
1. The ALL class is associated with the incoming packet.
2. Vendor class options are processed.
3. Classes with matching expressions and not marked for later ("on
request" or depending on the KNOWN/UNKNOWN builtin classes) evaluation
are processed in the order they are defined in the configuration: the
boolean expression is evaluated and when it returns true ("match") the
incoming packet is associated to the class.
4. If a private or code 43 DHCPv4 option is received, decoding it
following its client class or global (or for option 43 last resort)
definition.
5. Choose a subnet, possibly based on the class information when some
subnets are guarded. More precisely: when choosing a subnet, the
server will iterate over all of the subnets that are feasible given
the information found in the packet (client address, relay address
etc). It will use the first subnet it finds that either doesn't have a
class associated with it or that has a class which matches one of the
packet's classes.
6. Host reservations are looked for. If an identifier from the incoming
packet matches a host reservation in the subnet or shared network, the
packet is associated with the KNOWN class and all classes of the host
reservation. If a reservation is not found, the packet is assigned to
UNKNOWN class.
7. Classes with matching expressions using directly or indirectly the
KNOWN/UNKNOWN builtin classes and not marked for later ("on request")
evaluation are processed in the order they are defined in the
configuration: the boolean expression is evaluated and when it returns
true ("match") the incoming packet is associated to the class. The
determination whether there is a reservation for a given client is
made after a subnet is selected. As such, it is not possible to use
KNOWN/UNKNOWN classes to select a shared network or a subnet.
8. If needed, addresses and prefixes from pools are assigned, possibly
based on the class information when some pools are reserved to class
members.
9. Evaluate classes marked as "required" in the order in which they are
listed as required: first shared network, then the subnet and to
finally pools assigned resources belong too.
10. Assign options, again possibly based on the class information in order
classes were associated with the incoming packet. For DHCPv4 private
and code 43 options this includes class local option definitions.
Note
Beginning with Kea 1.4.0 release, client classes follow the order in which
they are specified in the configuration (vs. alphabetical order in
previous releases). Required classes follow the order in which they are
required.
When determining which options to include in the response, the server will
examine the union of options from all of the assigned classes. In case
when two or more classes include the same option, the value from the first
class examined will be used, and classes are examined in the order they
were associated so ALL is always the first class and matching required
classes are last.
As an example, imagine that an incoming packet matches two classes. Class
"foo" defines values for an NTP server (option 42 in DHCPv4) and an SMTP
server (option 69 in DHCPv4) while class "bar" defines values for an NTP
server and a POP3 server (option 70 in DHCPv4). The server will examine
the three options NTP, SMTP and POP3 and return any of them that the
client requested. As the NTP server was defined twice the server will
choose only one of the values for the reply: the class from which the
value is obtained is unspecified.
Note
Care should be taken with client classification as it is easy for clients
that do not meet class criteria to be denied any service altogether.
13.2. Builtin Client Classes
Some classes are builtin so do not need to be defined. The main example
uses Vendor Class information: The server checks whether an incoming
DHCPv4 packet includes the vendor class identifier option (60) or an
incoming DHCPv6 packet includes the vendor class option (16). If it does,
the content of that option is prepended with "VENDOR_CLASS_" and the
result is interpreted as a class. For example, modern cable modems will
send this option with value "docsis3.0" and so the packet will belong to
class "VENDOR_CLASS_docsis3.0".
The "HA_" prefix is used by the High Availability hooks library to
designate certain servers to process DHCP packets as a result of load
balancing. The class name is constructed by prepending the "HA_" prefix to
the name of the server which should process the DHCP packet. This server
will use appropriate pool or subnet to allocate IP addresses (and/or
prefixes) from, based on the assigned client classes. The details can be
found in Section 14.4.7, "ha: High Availability".
Other examples are: the ALL class which all incoming packets belong to,
and the KNOWN class assigned when host reservations exist for the
particular client. By convention, builtin classes' names begin with all
capital letters.
Currently recognized builtin class names are ALL, KNOWN and UNKNOWN, and
prefixes VENDOR_CLASS_, HA_, AFTER_ and EXTERNAL_. The AFTER_ prefix is a
provision for a not yet written hook, the EXTERNAL_ prefix can be freely
used: builtin classes are implicitly defined so never raise warnings if
they do not appear in the configuration.
13.3. Using Expressions In Classification
The expression portion of classification contains operators and values.
All values are currently strings and operators take a string or strings
and return another string. When all the operations have completed the
result should be a value of "true" or "false". The packet belongs to the
class (and the class name is added to the list of classes) if the result
is "true". Expressions are written in standard format and can be nested.
Expressions are pre-processed during the parsing of the configuration file
and converted to an internal representation. This allows certain types of
errors to be caught and logged during parsing. Examples of these errors
include an incorrect number or types of arguments to an operator. The
evaluation code will also check for this class of error and generally
throw an exception, though this should not occur in a normally functioning
system.
Other issues, for example the starting position of a substring being
outside of the substring or an option not existing in the packet, result
in the operator returning an empty string.
Expressions are a work in progress and the supported operators and values
are limited. The expectation is that additional operators and values will
be added over time, however the basic mechanisms will remain the same.
Dependencies between classes are checked too: for instance forward
dependencies are rejected when the configuration is parsed: an expression
can only depend on already defined classes (including builtin classes) and
which are evaluated in a previous or the same evaluation phase. This does
not apply to the KNOWN or UNKNOWN classes.
Table 13.1. List of Classification Values
+----------------------------------------------------------------------------------+
| Name | Example expression | Example value | Description |
|---------------+-----------------------------+----------------+-------------------|
|String literal |'example' |'example' |A string |
|---------------+-----------------------------+----------------+-------------------|
|Hexadecimal |0x5a7d |'Z}' |A hexadecimal |
|string literal | | |string |
|---------------+-----------------------------+----------------+-------------------|
|IP address |10.0.0.1 |0x0a000001 |An IP address |
|literal | | | |
|---------------+-----------------------------+----------------+-------------------|
|Integer literal|123 |'123' |A 32 bit unsigned |
| | | |integer value |
|----------------------------------------------------------------------------------|
|----------------------------------------------------------------------------------|
| | | |The value of the |
|Binary content |option[123].hex |'(content of the|option with given |
|of the option | |option)' |code from the |
| | | |packet as hex |
|---------------+-----------------------------+----------------+-------------------|
| | | |If the option with |
|Option | | |given code is |
|existence |option[123].exists |'true' |present in the |
| | | |packet "true" else |
| | | |"false" |
|---------------+-----------------------------+----------------+-------------------|
| | | |If the packet |
|Client class |member('foobar') |'true' |belongs to the |
|membership | | |given client class |
| | | |"true" else "false"|
|---------------+-----------------------------+----------------+-------------------|
| | | |If there is a host |
|Known client |known |member('KNOWN') |reservation for the|
| | | |client "true" else |
| | | |"false" |
|---------------+-----------------------------+----------------+-------------------|
| | | |If there is a host |
|Unknown client |unknown |not |reservation for the|
| | |member('KNOWN') |client "false" else|
| | | |"true" |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of |
|DHCPv4 relay | | |sub-option with |
|agent |relay4[123].hex |'(content of the|given code from the|
|sub-option | |RAI sub-option)'|DHCPv4 Relay Agent |
| | | |Information option |
| | | |(option 82) |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|DHCPv6 Relay | |(value of the |option with code |
|Options |relay6[nest].option[code].hex|option) |"code" from the |
| | | |relay encapsulation|
| | | |"nest" |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|DHCPv6 Relay | | |peer address field |
|Peer Address |relay6[nest].peeraddr |2001:DB8::1 |from the relay |
| | | |encapsulation |
| | | |"nest" |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|DHCPv6 Relay | | |link address field |
|Link Address |relay6[nest].linkaddr |2001:DB8::1 |from the relay |
| | | |encapsulation |
| | | |"nest" |
|---------------+-----------------------------+----------------+-------------------|
|Interface name | | |The name of the |
|of packet |pkt.iface |eth0 |incoming interface |
| | | |of a DHCP packet. |
|---------------+-----------------------------+----------------+-------------------|
|Source address | | |The IP source |
|of packet |pkt.src |10.1.2.3 |address of a DHCP |
| | | |packet. |
|---------------+-----------------------------+----------------+-------------------|
|Destination | | |The IP destination |
|address of |pkt.dst |10.1.2.3 |address of a DHCP |
|packet | | |packet. |
|---------------+-----------------------------+----------------+-------------------|
| | | |The length of a |
| | | |DHCP packet (UDP |
|Length of |pkt.len |513 |header field), |
|packet | | |expressed as a 32 |
| | | |bit unsigned |
| | | |integer. |
|---------------+-----------------------------+----------------+-------------------|
|Hardware | | |The value of the |
|address in |pkt4.mac |0x010203040506 |chaddr field of the|
|DHCPv4 packet | | |DHCPv4 packet, hlen|
| | | |(0 to 16) bytes |
|---------------+-----------------------------+----------------+-------------------|
|Hardware length| | |The value of the |
|in DHCPv4 |pkt4.hlen |6 |hlen field of the |
|packet | | |DHCPv4 packet |
| | | |padded to 4 bytes |
|---------------+-----------------------------+----------------+-------------------|
|Hardware type | | |The value of the |
|in DHCPv4 |pkt4.htype |6 |htype field of the |
|packet | | |DHCPv4 packet |
| | | |padded to 4 bytes |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|ciaddr field in|pkt4.ciaddr |192.0.2.1 |ciaddr field of the|
|DHCPv4 packet | | |DHCPv4 packet (IPv4|
| | | |address, 4 bytes) |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|giaddr field in|pkt4.giaddr |192.0.2.1 |giaddr field of the|
|DHCPv4 packet | | |DHCPv4 packet (IPv4|
| | | |address, 4 bytes) |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|yiaddr field in|pkt4.yiaddr |192.0.2.1 |yiaddr field of the|
|DHCPv4 packet | | |DHCPv4 packet (IPv4|
| | | |address, 4 bytes) |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|siaddr field in|pkt4.siaddr |192.0.2.1 |siaddr field of the|
|DHCPv4 packet | | |DHCPv4 packet (IPv4|
| | | |address, 4 bytes) |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
| | | |message type field |
|Message Type in|pkt4.msgtype |1 |in the DHCPv4 |
|DHCPv4 packet | | |packet (expressed |
| | | |as a 32 bit |
| | | |unsigned integer). |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|Transaction ID | | |transaction id in |
|(xid) in DHCPv4|pkt4.transid |12345 |the DHCPv4 packet |
|packet | | |(expressed as a 32 |
| | | |bit unsigned |
| | | |integer). |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
| | | |message type field |
|Message Type in|pkt6.msgtype |1 |in the DHCPv6 |
|DHCPv6 packet | | |packet (expressed |
| | | |as a 32 bit |
| | | |unsigned integer). |
|---------------+-----------------------------+----------------+-------------------|
| | | |The value of the |
|Transaction ID | | |transaction id in |
|in DHCPv6 |pkt6.transid |12345 |the DHCPv6 packet |
|packet | | |(expressed as a 32 |
| | | |bit unsigned |
| | | |integer). |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns whether a |
|Vendor option | | |vendor option from |
|existence (any |vendor[*].exists |true |any vendor is |
|vendor) | | |present ('true') or|
| | | |absent ('false'). |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns whether a |
|Vendor option | | |vendor option from |
|existence | | |specified vendor |
|(specific |vendor[4491].exists |true |(determined by its |
|vendor) | | |enterprise-id) is |
| | | |present ('true') or|
| | | |absent ('false'). |
|---------------+-----------------------------+----------------+-------------------|
| | | |If the vendor |
| | | |option is present, |
|Enterprise-id | | |it returns the |
|from vendor |vendor.enterprise |4491 |value of the |
|option | | |enterprise-id field|
| | | |padded to 4 bytes. |
| | | |Returns "" |
| | | |otherwise. |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns 'true' if |
| | | |there is vendor |
|Vendor | | |option with |
|sub-option |vendor[4491].option[1].exists|true |specified |
|existence | | |enterprise-id and |
| | | |given sub-option is|
| | | |present. Returns |
| | | |'false' otherwise. |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns content of |
| | | |the specified |
| | | |sub-option of a |
|Vendor | | |vendor option with |
|sub-option |vendor[4491].option[1].hex |docsis3.0 |specified |
|content | | |enterprise id. |
| | | |Returns '' if no |
| | | |such option or |
| | | |sub-option is |
| | | |present. |
|---------------+-----------------------------+----------------+-------------------|
|Vendor class | | |Returns whether a |
|option | | |vendor class option|
|existence (any |vendor-class[*].exists |true |from any vendor is |
|vendor) | | |present ('true') or|
| | | |absent ('false'). |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns whether a |
|Vendor class | | |vendor class option|
|option | | |from specified |
|existence |vendor-class[4491].exists |true |vendor (determined |
|(specific | | |by its |
|vendor) | | |enterprise-id) is |
| | | |present ('true') or|
| | | |absent ('false'). |
|---------------+-----------------------------+----------------+-------------------|
| | | |If the vendor |
| | | |option is present, |
|Enterprise-id | | |it returns the |
|from vendor |vendor-class.enterprise |4491 |value of the |
|class option | | |enterprise-id field|
| | | |padded to 4 bytes. |
| | | |Returns "" |
| | | |otherwise. |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns content of |
| | | |the first data |
|First data | | |chunk from the |
|chunk from |vendor-class[4491].data |docsis3.0 |vendor class option|
|vendor class | | |with specified |
|option | | |enterprise-id. |
| | | |Returns "" if |
| | | |missing. |
|---------------+-----------------------------+----------------+-------------------|
| | | |Returns content of |
| | | |the specified data |
|Specific data | | |chunk of a vendor |
|chunk from | | |class option with |
|vendor class |vendor-class[4491].data[3] |docsis3.0 |specified |
|option | | |enterprise id. |
| | | |Returns '' if no |
| | | |such option or data|
| | | |chunk is present. |
+----------------------------------------------------------------------------------+
Notes:
* Hexadecimal strings are converted into a string as expected. The
starting "0X" or "0x" is removed and if the string is an odd number of
characters a "0" is prepended to it.
* IP addresses are converted into strings of length 4 or 16. IPv4, IPv6,
and IPv4 embedded IPv6 (e.g., IPv4 mapped IPv6) addresses are
supported.
* Integers in an expression are converted to 32 bit unsigned integers
and are represented as four-byte strings. For example 123 is
represented as 0x0000007b. All expressions that return numeric values
use 32-bit unsigned integers, even if the field in the packet is
smaller. In general it is easier to use decimal notation to represent
integers, but it is also possible to use hex notation. When using hex
notation to represent an integer care should be taken to make sure the
value is represented as 32 bits, e.g. use 0x00000001 instead of 0x1 or
0x01. Also, make sure the value is specified in network order, e.g. 1
is represented as 0x00000001.
* "option[code].hex" extracts the value of the option with the code
"code" from the incoming packet. If the packet doesn't contain the
option, it returns the empty string. The string is presented as a byte
string of the option payload without the type code or length fields.
* "option[code].exists" checks if an option with the code "code" is
present in the incoming packet. It can be used with empty options.
* "member('foobar')" checks if the packet belongs to the client class
"foobar". To avoid dependency loops the configuration file parser
checks if client classes were already defined or are built-in, i.e.,
beginning by "VENDOR_CLASS_", "AFTER__" (for the to come "after" hook)
and "EXTERNAL_" or equal to "ALL", "KNOWN", "UNKNOWN"etc.
"known" and "unknown" are short hands for "member('KNOWN')" and "not
member('KNOWN')". Note the evaluation of any expression using directly
or indirectly the "KNOWN" class is deferred after the host reservation
lookup (i.e. when the "KNOWN" or "UNKNOWN" partition is determined).
* "relay4[code].hex" attempts to extract the value of the sub-option
"code" from the option inserted as the DHCPv4 Relay Agent Information
(82) option. If the packet doesn't contain a RAI option, or the RAI
option doesn't contain the requested sub-option, the expression
returns an empty string. The string is presented as a byte string of
the option payload without the type code or length fields. This
expression is allowed in DHCPv4 only.
* "relay4" shares the same representation types as "option", for
instance "relay4[code].exists" is supported.
* "relay6[nest]" allows access to the encapsulations used by any DHCPv6
relays that forwarded the packet. The "nest" level specifies the relay
from which to extract the information, with a value of 0 indicating
the relay closest to the DHCPv6 server. Negative values allow to
specify relays counted from the DHCPv6 client, -1 indicating the relay
closest to the client. In general negative "nest" level is the same as
the number of relays + "nest" level. If the requested encapsulation
doesn't exist an empty string "" is returned. This expression is
allowed in DHCPv6 only.
* "relay6[nest].option[code]" shares the same representation types as
"option", for instance "relay6[nest].option[code].exists" is
supported.
* Expressions starting with "pkt4" can be used only in DHCPv4. They
allows access to DHCPv4 message fields.
* "pkt6" refers to information from the client request. To access any
information from an intermediate relay use "relay6". "pkt6.msgtype"
and "pkt6.transid" output a 4 byte binary string for the message type
or transaction id. For example the message type SOLICIT will be
"0x00000001" or simply 1 as in "pkt6.msgtype == 1".
* Vendor option means Vendor-Identifying Vendor-specific Information
option in DHCPv4 (code 125, see Section 4 of RFC 3925) and
Vendor-specific Information Option in DHCPv6 (code 17, defined in
Section 22.17 of RFC 3315). Vendor class option means
Vendor-Identifying Vendor Class Option in DHCPv4 (code 124, see
Section 3 of RFC 3925) in DHCPv4 and Class Option in DHCPv6 (code 16,
see Section 22.16 of RFC 3315). Vendor options may have sub-options
that are referenced by their codes. Vendor class options do not have
sub-options, but rather data chunks, which are referenced by index
value. Index 0 means the first data chunk, Index 1 is for the second
data chunk (if present), etc.
* In the vendor and vendor-class constructs Asterisk (*) or 0 can be
used to specify a wildcard enterprise-id value, i.e. it will match any
enterprise-id value.
* Vendor Class Identifier (option 60 in DHCPv4) can be accessed using
option[60] expression.
* RFC3925 and RFC3315 allow for multiple instances of vendor options to
appear in a single message. The client classification code currently
examines the first instance if more than one appear. For
vendor.enterprise and vendor-class.enterprise expressions, the value
from the first instance is returned. Please submit a feature request
on Kea website if you need support for multiple instances.
Table 13.2. List of Classification Expressions
+------------------------------------------------------------------------+
| Name | Example | Description |
|-----------+--------------------------------+---------------------------|
| | | Compare the two values |
| Equal | 'foo' == 'bar' | and return "true" or |
| | | "false" |
|-----------+--------------------------------+---------------------------|
| Not | not ('foo' == 'bar') | Logical negation |
|-----------+--------------------------------+---------------------------|
| And | ('foo' == 'bar') and ('bar' == | Logical and |
| | 'foo') | |
|-----------+--------------------------------+---------------------------|
| Or | ('foo' == 'bar') or ('bar' == | Logical or |
| | 'foo') | |
|-----------+--------------------------------+---------------------------|
| Substring | substring('foobar',0,3) | Return the requested |
| | | substring |
|-----------+--------------------------------+---------------------------|
| Concat | concat('foo','bar') | Return the concatenation |
| | | of the strings |
|-----------+--------------------------------+---------------------------|
| | ifelse('foo' == | Return the branch value |
| Ifelse | 'bar','us','them') | according to the |
| | | condition |
+------------------------------------------------------------------------+
13.3.1. Logical operators
The Not, And and Or logical operators are the common operators. Not has
the highest precedence and Or the lowest. And and Or are (left)
associative, parentheses around a logical expression can be used to
enforce a specific grouping, for instance in "A and (B or C)" (without
parentheses "A and B or C" means "(A and B) or C").
13.3.2. Substring
The substring operator "substring(value, start, length)" accepts both
positive and negative values for the starting position and the length. For
"start", a value of 0 is the first byte in the string while -1 is the last
byte. If the starting point is outside of the original string an empty
string is returned. "length" is the number of bytes to extract. A negative
number means to count towards the beginning of the string but doesn't
include the byte pointed to by "start". The special value "all" means to
return all bytes from start to the end of the string. If length is longer
than the remaining portion of the string then the entire remaining portion
is returned. Some examples may be helpful:
substring('foobar', 0, 6) == 'foobar'
substring('foobar', 3, 3) == 'bar'
substring('foobar', 3, all) == 'bar'
substring('foobar', 1, 4) == 'ooba'
substring('foobar', -5, 4) == 'ooba'
substring('foobar', -1, -3) == 'oba'
substring('foobar', 4, -2) == 'ob'
substring('foobar', 10, 2) == ''
13.3.3. Concat
The concat function "concat(string1, string2)" returns the concatenation
of its two arguments. For instance:
concat('foo', 'bar') == 'foobar'
13.3.4. Ifelse
The ifelse function "ifelse(cond, iftrue, ifelse)" returns the "iftrue" or
"ifelse" branch value following the boolean condition "cond". For
instance:
ifelse(option[230].exists, option[230].hex, 'none')
Note
The expression for each class is executed on each packet received. If the
expressions are overly complex, the time taken to execute them may impact
the performance of the server. If you need complex or time consuming
expressions you should write a hook to perform the necessary work.
13.4. Configuring Classes
A class contains five items: a name, a test expression, option data,
option definition and only-if-required flag. The name must exist and must
be unique amongst all classes. The test expression, option data and
definition, and only-if-required flag are optional.
The test expression is a string containing the logical expression used to
determine membership in the class. The entire expression is in double
quotes.
The option data is a list which defines any options that should be
assigned to members of this class.
The option definition is for DHCPv4 option 43 (Section 8.2.11, "DHCPv4
Vendor Specific Options" and DHCPv4 private options (Section 8.2.10,
"DHCPv4 Private Options").
Usually the test expression is evaluated before subnet selection but in
some cases it is useful to evaluate it later when the subnet,
shared-network or pools are known but output option processing not yet
done. The only-if-required flag, false by default, allows to perform the
evaluation of the test expression only when it was required, i.e. in a
require-client-classes list of the selected subnet, shared-network or
pool.
The require-client-classes list which is valid for shared-network, subnet
and pool scope specifies the classes which are evaluated in the second
pass before output option processing. The list is built in the reversed
precedence order of option data, i.e. an option data in a subnet takes
precedence on one in a shared-network but required class in a subnet is
added after one in a shared-network. The mechanism is related to the
only-if-required flag but it is not mandatory that the flag was set to
true.
In the following example the class named "Client_foo" is defined. It is
comprised of all clients whose client ids (option 61) start with the
string "foo". Members of this class will be given 192.0.2.1 and 192.0.2.2
as their domain name servers.
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],
...
}
This example shows a client class being defined for use by the DHCPv6
server. In it the class named "Client_enterprise" is defined. It is
comprised of all clients who's client identifiers start with the given hex
string (which would indicate a DUID based on an enterprise id of
0xAABBCCDD). Members of this class will be given an 2001:db8:0::1 and
2001:db8:2::1 as their domain name servers.
"Dhcp6": {
"client-classes": [
{
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
],
...
}
13.5. Using Static Host Reservations In Classification
Classes can be statically assigned to the clients using techniques
described in Section 8.3.6, "Reserving Client Classes in DHCPv4" and
Section 9.3.5, "Reserving Client Classes in DHCPv6".
13.6. Configuring Subnets With Class Information
In certain cases it beneficial to restrict access to certain subnets only
to clients that belong to a given class, using the "client-class" keyword
when defining the subnet.
Let's assume that the server is connected to a network segment that uses
the 192.0.2.0/24 prefix. The Administrator of that network has decided
that addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed
by the DHCP4 server. Only clients belonging to client class Client_foo are
allowed to use this subnet. Such a configuration can be achieved in the
following way:
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
"client-class": "Client_foo"
},
...
],,
...
}
The following example shows restricting access to a DHCPv6 subnet. This
configuration will restrict use of the addresses 2001:db8:1::1 to
2001:db8:1::FFFF to members of the "Client_enterprise" class.
"Dhcp6": {
"client-classes": [
{
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
"client-class": "Client_enterprise"
}
],
...
}
13.7. Configuring Pools With Class Information
Similar to subnets in certain cases access to certain address or prefix
pools must be restricted to only clients that belong to a given class,
using the "client-class" when defining the pool.
Let's assume that the server is connected to a network segment that uses
the 192.0.2.0/24 prefix. The Administrator of that network has decided
that addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed
by the DHCP4 server. Only clients belonging to client class Client_foo are
allowed to use this pool. Such a configuration can be achieved in the
following way:
"Dhcp4": {
"client-classes": [
{
"name": "Client_foo",
"test": "substring(option[61].hex,0,3) == 'foo'",
"option-data": [
{
"name": "domain-name-servers",
"code": 6,
"space": "dhcp4",
"csv-format": true,
"data": "192.0.2.1, 192.0.2.2"
}
]
},
...
],
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{
"pool": "192.0.2.10 - 192.0.2.20",
"client-class": "Client_foo"
}
]
},
...
],,
}
The following example shows restricting access to an address pool. This
configuration will restrict use of the addresses 2001:db8:1::1 to
2001:db8:1::FFFF to members of the "Client_enterprise" class.
"Dhcp6": {
"client-classes": [
{
"name": "Client_enterprise_",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff",
"client-class": "Client_foo"
}
]
},
...
],
...
}
13.8. Using Classes
Currently classes can be used for two functions. They can supply options
to the members of the class and they can be used to choose a subnet from
which an address will be assigned to the class member.
When supplying options, options defined as part of the class definition
are considered "class globals". They will override any global options that
may be defined and in turn will be overridden by any options defined for
an individual subnet.
13.9. Classes and Hooks
You may use a hook to classify your packets. This may be useful if the
expression would either be complex or time consuming and be easier or
better to write as code. Once the hook has added the proper class name to
the packet the rest of the classification system will work as normal in
choosing a subnet and selecting options. For a description of hooks see
Chapter 14, Hooks Libraries, for a description on configuring classes see
Section 13.4, "Configuring Classes" and Section 13.6, "Configuring Subnets
With Class Information".
13.10. Debugging Expressions
While you are constructing your classification expressions you may find it
useful to enable logging see Chapter 18, Logging for a more complete
description of the logging facility.
To enable the debug statements in the classification system you will need
to set the severity to "DEBUG" and the debug level to at least 55. The
specific loggers are "kea-dhcp4.eval" and "kea-dhcp6.eval".
In order to understand the logging statements one must understand a bit
about how expressions are evaluated, for a more complete description refer
to the design document at http://kea.isc.org/wiki/KeaDesigns. In brief
there are two structures used during the evaluation of an expression: a
list of tokens which represent the expressions and a value stack which
represents the values being manipulated.
The list of tokens is created when the configuration file is processed
with most expressions and values being converted to a token. The list is
organized in reverse Polish notation. During execution, the list will be
traversed in order. As each token is executed it will be able to pop
values from the top of the stack and eventually push its result on the top
of the stack. Imagine the following expression:
"test": "substring(option[61].hex,0,3) == 'foo'",
This will result in the following tokens:
option, number (0), number (3), substring, text ('foo'), equals
In this example the first three tokens will simply push values onto the
stack. The substring token will then remove those three values and compute
a result that it places on the stack. The text option also places a value
on the stack and finally the equals token removes the two tokens on the
stack and places its result on the stack.
When debug logging is enabled, each time a token is evaluated it will emit
a log message indicating the values of any objects that were popped off of
the value stack and any objects that were pushed onto the value stack.
The values will be displayed as either text if the command is known to use
text values or hexadecimal if the command either uses binary values or can
manipulate either text or binary values. For expressions that pop multiple
values off the stack, the values will be displayed in the order they were
popped. For most expressions this won't matter but for the concat
expression the values are displayed in reverse order from how they are
written in the expression.
Let us assume that the following test has been entered into the
configuration. This example skips most of the configuration to concentrate
on the test.
"test": "substring(option[61].hex,0,3) == 'foo'",
The logging might then resemble this:
2016-05-19 13:35:04.163 DEBUG [kea.eval/44478] EVAL_DEBUG_OPTION Pushing option 61 with value 0x666F6F626172
2016-05-19 13:35:04.164 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '0'
2016-05-19 13:35:04.165 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '3'
2016-05-19 13:35:04.166 DEBUG [kea.eval/44478] EVAL_DEBUG_SUBSTRING Popping length 3, start 0, string 0x666F6F626172 pushing result 0x666F6F
2016-05-19 13:35:04.167 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string 'foo'
2016-05-19 13:35:04.168 DEBUG [kea.eval/44478] EVAL_DEBUG_EQUAL Popping 0x666F6F and 0x666F6F pushing result 'true'
Note
The debug logging may be quite verbose if you have a number of expressions
to evaluate. It is intended as an aid in helping you create and debug your
expressions. You should plan to disable debug logging when you have your
expressions working correctly. You also may wish to include only one set
of expressions at a time in the configuration file while debugging them in
order to limit the log statements. For example when adding a new set of
expressions you might find it more convenient to create a configuration
file that only includes the new expressions until you have them working
correctly and then add the new set to the main configuration file.
Chapter 14. Hooks Libraries
Table of Contents
14.1. Introduction
14.2. Installing Hook packages
14.3. Configuring Hooks Libraries
14.4. Available Hooks Libraries
14.4.1. user_chk: Checking User Access
14.4.2. legal_log: Forensic Logging Hooks
14.4.3. flex_id: Flexible Identifiers for Host Reservations
14.4.4. host_cmds: Host Commands
14.4.5. lease_cmds: Lease Commands
14.4.6. subnet_cmds: Subnet Commands
14.4.7. ha: High Availability
14.4.8. radius: RADIUS server support
14.4.9. host_cache: Caching Host Reservations
14.4.10. stat_cmds: Supplemental Statistics Commands
14.5. User contexts
14.1. Introduction
Although Kea offers a lot of flexibility, there may be cases where its
behavior needs customization. To accommodate this possibility, Kea
includes the idea of "Hooks". This feature lets Kea load one or more
dynamically-linked libraries (known as "hooks libraries") and, at various
points in its processing ("hook points"), call functions in them. Those
functions perform whatever custom processing is required.
The hooks concept also allows keeping the core Kea code reasonably small
by moving features that some, but not all users find useful to external
libraries. People who don't need specific functionality simply don't load
the libraries.
Hooks libraries are loaded by individual Kea processes, not to Kea as a
whole. This means (for example) that it is possible to associate one set
of libraries with the DHCP4 server and a different set to the DHCP6
server.
Another point to note is that it is possible for a process to load
multiple libraries. When processing reaches a hook point, Kea calls the
hooks library functions attached to it. If multiple libraries have
attached a function to a given hook point, Kea calls all of them, in the
order in which the libraries are specified in the configuration file. The
order may be important: consult the documentation of the libraries to see
if this is the case.
The next section describes how to configure hooks libraries. If you are
interested in writing your own hooks library, information can be found in
the Kea Developer's Guide.
Note that some libraries are available under different licenses.
Note that some libraries may require additional dependencies and/or
compilation switches to be enabled, e.g. Radius library introduced in Kea
1.4 requires FreeRadius-client library to be present. If
--with-free-radius option is not specified, the Radius library will not be
built.
14.2. Installing Hook packages
Note
The installation procedure has changed in 1.4.0. Kea 1.3.0 and earlier
needed special switches passed to configure script to detect the hook
libraries. Please see this KB article: https://kb.isc.org/article/AA-01587
.
Some hook packages are included in the base Kea sources. There is no need
to do anything special to compile or install them, they are covered by the
usual building and installation procedure. ISC also provides several
additional hooks in form of various packages. All of those packages follow
the same installation procedure that is similar to base Kea, but has
several additional steps. For your convenience, the whole procedure is
described here. Please refer to Chapter 3, Installation for general
overview.
1. Download the package. You will receive detailed instructions how to get
it separately. This will be a file with a name similar to
kea-premium-1.4.0.tar.gz. Your name may differ depending on which package
you got.
2. If you have the sources for the corresponding version of the
open-source Kea package still on your system (from when you installed
Kea), skip this step. Otherwise extract the Kea source from the original
tarball you downloaded. For example, if you downloaded Kea 1.4.0., you
should have a tarball called kea-1.4.0.tar.gz on your system. Unpack this
tarball:
$ tar zxvf kea-1.4.0.tar.gz
This will unpack the tarball into the kea-1.4.0 subdirectory of your
current working directory.
3. Unpack the Kea premium tarball into the directory into which Kea was
unpacked. For example, assuming that you followed step 2 and that Kea
1.4.0 has been unpacked into a kea-1.4.0 subdirectory and that the Kea
premium tarball is in your current directory, the following steps will
unpack the premium tarball into the correct location:
$ cd kea-1.4.0
$ tar xvf ../kea-premium-1.4.0.tar.gz
Note that unpacking the Kea premium package will put the files into a
directory named premium. Regardless of the name of your package, the
directory will always be called premium, just its content may vary.
4. Run autoreconf tools. This step is necessary to update Kea's build
script to include additional directory. If this tool is not already
available on your system, you need to install automake and autoconf tools.
To generate configure script, please use:
$ autoreconf -i
5. Rerun configure, using the same configure options as you used when
originally building Kea. You can check if configure has detected the
premium package by inspecting the summary printed when it exits. The first
section of the output should look something like:
Package:
Name: kea
Version: 1.4.0
Extended version:1.4.0 (tarball)
OS Family: Linux
Using GNU sed: yes
Premium package: yes
Included Hooks: forensic_log flex_id host_cmds
The last line indicates which specific hooks were detected. Note that some
hooks may require its own dedicated switches, e.g. radius hook requires
extra switches for FreeRADIUS. Please consult later sections of this
chapter for details.
6. Rebuild Kea
$ make
If your machine has multiple CPU cores, interesting option to consider
here is -j X, where X is the number of available cores.
7. Install Kea sources together with hooks:
$ sudo make install
Note that as part of the installation procedure, the install script will
eventually venture into premium/ directory and will install additional
hook libraries and associated files.
The installation location of the hooks libraries depends whether you
specified --prefix parameter to the configure script. If you did not, the
default location will be /usr/local/lib/hooks. You can verify the
libraries are installed properly with this command:
$ ls -l /usr/local/lib/hooks/*.so
/usr/local/lib/hooks/libdhcp_flex_id.so
/usr/local/lib/hooks/libdhcp_host_cmds.so
/usr/local/lib/hooks/libdhcp_lease_cmds.so
/usr/local/lib/hooks/libdhcp_legal_log.so
/usr/local/lib/hooks/libdhcp_subnet_cmds.so
The exact list you see will depend on the packages you have. If you
specified directory via --prefix, the hooks libraries will be located in
{prefix directory}/lib/hooks.
14.3. Configuring Hooks Libraries
The hooks libraries for a given process are configured using the
hooks-libraries keyword in the configuration for that process. (Note that
the word "hooks" is plural). The value of the keyword is an array of map
structures, each structure corresponding to a hooks library. For example,
to set up two hooks libraries for the DHCPv4 server, the configuration
would be:
"Dhcp4": {
:
"hooks-libraries": [
{
"library": "/opt/charging.so"
},
{
"library": "/opt/local/notification.so",
"parameters": {
"mail": "spam@example.com",
"floor": 13,
"debug": false,
"users": [ "alice", "bob", "charlie" ],
"languages": {
"french": "bonjour",
"klingon": "yl'el"
}
}
}
]
:
}
Note
This is a change to the syntax used in Kea 0.9.2 and earlier, where
hooks-libraries was a list of strings, each string being the name of a
library. The change was made in Kea 1.0 to facilitate the specification of
library-specific parameters, a capability available in Kea 1.1.0 onwards.
Libraries should allow a parameter entry where to put comments as it is
done for many configuration scopes with comment and user context.
Note
The library reloading behavior has changed in Kea 1.1. Libraries are
reloaded, even if their list hasn't changed. Kea does that, because the
parameters specified for the library (or the files those parameters point
to) may have changed.
Libraries may have additional parameters. Those are not mandatory in the
sense that there may be libraries that don't require them. However, for
specific library there is often specific requirement for specify certain
set of parameters. Please consult the documentation for your library for
details. In the example above, the first library has no parameters. The
second library has five parameters, specifying mail (string parameter),
floor (integer parameter), debug (boolean parameter) and even lists (list
of strings) and maps (containing strings). Nested parameters could be used
if the library supports it. This topic is explained in detail in the Hooks
Developer's Guide in the "Configuring Hooks Libraries" section.
Notes:
* The full path to each library should be given.
* As noted above, order may be important - consult the documentation for
each library.
* An empty list has the same effect as omitting the hooks-libraries
configuration element all together.
Note
There is one case where this is not true: if Kea is running with a
configuration that contains a hooks-libraries item, and that item is
removed and the configuration reloaded, the removal will be ignored
and the libraries remain loaded. As a workaround, instead of removing
the hooks-libraries item, change it to an empty list. This will be
fixed in a future version of Kea.
At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
hooks libraries.
14.4. Available Hooks Libraries
As described above, the hooks functionality provides a way to customize a
Kea server without modifying the core code. ISC has chosen to take
advantage of this feature to provide functions that may only be useful to
a subset of Kea users. To this end ISC has created some hooks libraries;
these discussed in the following sections.
Note
Some of these libraries will be available with the base code while others
will be shared with organizations supporting development of Kea , possibly
as a 'benefit' or 'thank you' for helping to sustain the larger Kea
project. If you would like to get access to those libraries, please
consider taking out a support contract: this includes professional
support, advance security notifications, input into our roadmap planning,
and many other benefits, while helping making Kea sustainable in the long
term.
The following table provides a list of libraries currently available from
ISC. It is important to pay attention to which libraries may be loaded by
which Kea processes. It is a common mistake to configure the
kea-ctrl-agent process to load libraries that should, in fact, be loaded
by the kea-dhcp4 or kea-dhcp6 processes. If a library from ISC doesn't
work as expected, please make sure that it has been loaded by the correct
process per the table below.
Warning
While the Kea Control Agent includes the "hooks" functionality, (i.e.
hooks libraries can be loaded by this process), none of ISC's current
hooks libraries should be loaded by the Control Agent.
Table 14.1. List of available hooks libraries
+----------------------------------------------------------------------------------------+
| Name |Availability| Since | Load by | Description |
| | | | process | |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |Reads known users list from a file. |
| | | | |Unknown users will be assigned a lease |
| | | | |from the last subnet defined in the |
| | | | |configuration file, e.g. to redirect them |
|user_chk |Kea sources |Kea 0.8|kea-dhcp4|a captive portal. This demonstrates how an|
| | | |kea-dhcp6|external source of information can be used|
| | | | |to influence the Kea allocation engine. |
| | | | |This hook is part of the Kea source code |
| | | | |and is available in the |
| | | | |src/hooks/dhcp/user_chk directory. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |This library provides hooks that record a |
| | | | |detailed log of lease assignments and |
| | | | |renewals into a set of log files. In many |
| | | | |legal jurisdictions companies, especially |
| | | | |ISPs, must record information about the |
| | | | |addresses they have leased to DHCP |
|Forensic |Support |Kea |kea-dhcp4|clients. This library is designed to help |
|Logging |customers |1.1.0 |kea-dhcp6|with that requirement. If the information |
| | | | |that it records is sufficient it may be |
| | | | |used directly. If your jurisdiction |
| | | | |requires that you save a different set of |
| | | | |information, you may use it as a template |
| | | | |or example and create your own custom |
| | | | |logging hooks. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |Kea software provides a way to handle host|
| | | | |reservations that include addresses, |
| | | | |prefixes, options, client classes and |
| | | | |other features. The reservation can be |
| | | | |based on hardware address, DUID, |
| | | | |circuit-id or client-id in DHCPv4 and |
| | | | |using hardware address or DUID in DHCPv6. |
| | | | |However, there are sometimes scenarios |
| | | | |where the reservation is more complex, |
|Flexible |Support |Kea |kea-dhcp4|e.g. uses other options that mentioned |
|Identifier |customers |1.2.0 |kea-dhcp6|above, uses part of specific options or |
| | | | |perhaps even a combination of several |
| | | | |options and fields to uniquely identify a |
| | | | |client. Those scenarios are addressed by |
| | | | |the Flexible Identifiers hook application.|
| | | | |It allows defining an expression, similar |
| | | | |to the one used in client classification, |
| | | | |e.g. substring(relay6[0].option[37],0,6). |
| | | | |Each incoming packet is evaluated against |
| | | | |that expression and its value is then |
| | | | |searched in the reservations database. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |Kea provides a way to store host |
| | | | |reservations in a database. In many larger|
| | | | |deployments it is useful to be able to |
| | | | |manage that information while the server |
| | | | |is running. This library provides |
| | | | |management commands for adding, querying |
| | | | |and deleting host reservations in a safe |
| | | | |way without restarting the server. In |
|Host Commands |Support |Kea |kea-dhcp4|particular, it validates the parameters, |
| |customers |1.2.0 |kea-dhcp6|so an attempt to insert incorrect data, |
| | | | |e.g. add a host with conflicting |
| | | | |identifier in the same subnet will be |
| | | | |rejected. Those commands are exposed via |
| | | | |command channel (JSON over unix sockets) |
| | | | |and Control Agent (JSON over RESTful |
| | | | |interface). Additional commands and |
| | | | |capabilities related to host reservations |
| | | | |will be added in the future. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |In deployments in which subnet |
| | | | |configuration needs to be frequently |
| | | | |updated, it is a hard requirement that |
| | | | |such updates be performed without the need|
| | | | |for a full DHCP server reconfiguration or |
| | | | |restart. This hooks library allows for |
|Subnet |Support |Kea |kea-dhcp4|incremental changes to the subnet |
|Commands |customers |1.3.0 |kea-dhcp6|configuration such as: adding a subnet, |
| | | | |removing a subnet. It also allows for |
| | | | |listing all available subnets and fetching|
| | | | |detailed information about a selected |
| | | | |subnet. The commands exposed by this |
| | | | |library do not affect other subnets or |
| | | | |configuration parameters currently used by|
| | | | |the server. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |The lease commands hook library offers a |
| | | | |number of new commands used to manage |
| | | | |leases. Kea provides a way to store lease |
| | | | |information in various backends: memfile, |
| | | | |MySQL, PostgreSQL and Cassandra. This |
| | | | |library provides a unified interface that |
| | | | |can manipulate leases in an unified, safe |
| | |Kea |kea-dhcp4|way. In particular, it allows: manipulate |
|Lease Commands|Kea sources |1.3.0 |kea-dhcp6|leases in memfile while Kea is running, |
| | | | |sanity check changes, check lease |
| | | | |existence and remove all leases belonging |
| | | | |to specific subnet. It can also catch more|
| | | | |obscure errors, like adding a lease with |
| | | | |subnet-id that does not exist in the |
| | | | |configuration or configuring a lease to |
| | | | |use an address that is outside of the |
| | | | |subnet to which it is supposed to belong. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |Minimizing a risk of DHCP service |
| | | | |unavailability is achieved by setting up a|
| | | | |pair of the DHCP servers in a network. Two|
| | | | |modes of operation are supported. The |
| | | | |first one is called load balancing and is |
| | | | |sometimes referred to as active-active. |
| | | | |Each server can handle selected group of |
| | | | |clients in this network or all clients, if|
| | | | |it detects that its partner has became |
| | | | |unavailable. It is also possible to |
| | | | |designate one server to serve all DHCP |
| | | | |clients, and leave another server as |
| | | | |"standby". This mode is called hot standby|
|High |Kea sources |Kea |kea-dhcp4|and is sometimes referenced to as |
|Availability | |1.4.0 |kea-dhcp6|active-passive. This server will activate |
| | | | |its DHCP function when it detects that its|
| | | | |partner is not available. Such cooperation|
| | | | |between the DHCP servers requires that |
| | | | |these servers constantly communicate with |
| | | | |each other to send updates about allocated|
| | | | |leases and to periodically test whether |
| | | | |their partners are still operational. The |
| | | | |hook library also provides an ability to |
| | | | |send lease updates to external backup |
| | | | |server, making it much easier to have a |
| | | | |replacement that is almost up to date. The|
| | | | |"libdhcp_ha" library provides such |
| | | | |functionality for Kea DHCP servers. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |The RADIUS Hook library allows Kea to |
| | | | |interact with the RADIUS servers using |
| | | | |access and accounting mechanisms. The |
| | | | |access mechanism may be used for access |
| |Support |Kea |kea-dhcp4|control, assigning specific IPv4 or IPv6 |
|Radius |customers |1.4.0 |kea-dhcp6|addresses reserved by RADIUS, dynamically |
| | | | |assigning addresses from designated pools |
| | | | |chosen by RADIUS or rejecting the client's|
| | | | |messages altogether. The accounting |
| | | | |mechanism allows RADIUS server to keep |
| | | | |track of device activity over time. |
|--------------+------------+-------+---------+------------------------------------------|
| | | | |Some of the database backends, such as |
| | | | |RADIUS, are considered slow and may take a|
| | | | |long time to respond. Since Kea in general|
| | | | |is synchronous, the backend performance |
| | | | |directly affects the DHCP performance. To |
|Host Cache |Support |Kea |kea-dhcp4|minimize the impact and improve |
| |customers |1.4.0 |kea-dhcp6|performance, the Host Cache library |
| | | | |provides a way to cache responses from |
| | | | |other hosts. This includes negative |
| | | | |caching, i.e. the ability to remember that|
| | | | |there is no client information in the |
| | | | |database. |
+----------------------------------------------------------------------------------------+
ISC hopes to see more hooks libraries become available as time progresses,
both developed internally and externally. Since this list may evolve
dynamically, we decided to keep it on a wiki page, available at this link:
http://kea.isc.org/wiki/Hooks. If you are a developer or are aware of any
hooks libraries not listed there, please send a note to the kea-users or
kea-dev mailing lists and someone will update it.
The libraries developed by ISC are described in detail in the following
sections.
14.4.1. user_chk: Checking User Access
The user_chk library is the first hooks library published by ISC. It
attempts to serve several purposes:
* To assign "new" or "unregistered" users to a restricted subnet, while
"known" or "registered" users are assigned to unrestricted subnets.
* To allow DHCP response options or vendor option values to be
customized based upon user identity.
* To provide a real time record of the user registration activity which
can be sampled by an external consumer.
* To serve as a demonstration of various capabilities possible using the
hooks interface.
Once loaded, the library allows segregating incoming requests into known
and unknown clients. For known clients, the packets are processed mostly
as usual, except it is possible to override certain options being sent.
That can be done on a per host basis. Clients that are not on the known
hosts list will be treated as unknown and will be assigned to the last
subnet defined in the configuration file.
As an example of use, this behavior may be used to put unknown users into
a separate subnet that leads to a walled garden, where they can only
access a registration portal. Once they fill in necessary data, their
details are added to the known clients file and they get a proper address
after their device is restarted.
Note
This library was developed several years before the host reservation
mechanism has become available. Currently host reservation is much more
powerful and flexible, but nevertheless the user_chk capability to consult
and external source of information about clients and alter Kea's behavior
is useful and remains of educational value.
The library reads the /tmp/user_chk_registry.txt file while being loaded
and each time an incoming packet is processed. The file is expected to
have each line contain a self-contained JSON snippet which must have the
following two entries:
* type, whose value is "HW_ADDR" for IPv4 users or "DUID" for IPv6 users
* id, whose value is either the hardware address or the DUID from the
request formatted as a string of hex digits, with or without ":"
delimiters.
and may have the zero or more of the following entries:
* bootfile whose value is the pathname of the desired file
* tftp_server whose value is the hostname or IP address of the desired
server
A sample user registry file is shown below:
{ "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:04", "bootfile" : "/tmp/v4bootfile" }
{ "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:06", "tftp_server" : "tftp.v4.example.com" }
{ "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:04", "bootfile" : "/tmp/v6bootfile" }
{ "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:06", "tftp_server" : "tftp.v6.example.com" }
As with any other hooks libraries provided by ISC, internals of the
user_chk code are well documented. You can take a look at the Kea
Developer's Guide section dedicated to the user_chk library that discusses
how the code works internally. That, together with our general entries in
Hooks Framework section should give you some pointers how to extend this
library and perhaps even write your own from scratch.
14.4.2. legal_log: Forensic Logging Hooks
This section describes the forensic log hooks library. This library
provides hooks that record a detailed log of lease assignments and
renewals into a set of log files. Currently this library is only available
to ISC customers with a support contract.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
In many legal jurisdictions companies, especially ISPs, must record
information about the addresses they have leased to DHCP clients. This
library is designed to help with that requirement. If the information that
it records is sufficient it may be used directly. If your jurisdiction
requires that you save a different set of information you may use it as a
template or example and create your own custom logging hooks.
This logging is done as a set of hooks to allow it to be customized to any
particular need. Modifying a hooks library is easier and safer than
updating the core code. In addition by using the hooks features those
users who don't need to log this information can leave it out and avoid
any performance penalties.
14.4.2.1. Log File Naming
The names for the log files have the following form:
path/base-name.CCYYMMDD.txt
The "path" and "base-name" are supplied in the configuration as described
below see Section 14.4.2.4, "Configuring the Forensic Log Hooks". The next
part of the name is the date the log file was started, with four digits
for year, two digits for month and two digits for day. The file is rotated
on a daily basis.
Note
When running Kea servers for both DHCPv4 and DHCPv6 the log names must be
distinct. See the examples in Section 14.4.2.4, "Configuring the Forensic
Log Hooks".
14.4.2.2. DHCPv4 Log Entries
For DHCPv4 the library creates entries based on DHCPREQUEST messages and
corresponding DHCPv4 leases intercepted by lease4_select (for new leases)
and lease4_renew (for renewed leases) hooks.
An entry is a single string with no embedded end-of-line markers, a
prepended timestamp and has the following sections:
timestamp address duration device-id {client-info} {relay-info}
Where:
* timestamp - the current date and time the log entry was written in
"%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).
* address - the leased IPv4 address given out and whether it was
assigned or renewed.
* duration - the lease lifetime expressed in days (if present), hours,
minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
with the text "infinite duration".
* device-id - the client's hardware address shown as numerical type and
hex digit string.
* client-info - the DHCP client id option (61) if present, shown as a
hex string.
* relay-info - for relayed packets the giaddr and the RAI circuit-id,
remote-id and subscriber-id options (option 82 sub options: 1, 2 and
6) if present. The circuit id and remote id are presented as hex
strings
For instance (line breaks added for readability, they would not be present
in the log file).
2018-01-06 01:02:03 CET Address: 192.2.1.100 has been renewed for 1 hrs 52 min 15 secs to a device with hardware address:
hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33,
identified by circuit-id: 68:6f:77:64:79 and remote-id: 87:f6:79:77:ef
In addition to logging lease activity driven by DHCPv4 client traffic, it
also logs entries for the following lease management control channel
commands: lease4-add, lease4-update, and lease4-del. Each entry is a
single string with no embedded end-of-line markers and they will typically
have the following forms:
lease4-add:
*timestamp* Administrator added a lease of address: *address* to a device with hardware address: *device-id*
Dependent on the arguments of the add command, it may also include the
client-id and duration.
Example:
2018-01-06 01:02:03 CET Administrator added a lease of address: 192.0.2.202 to a device with hardware address:
1a:1b:1c:1d:1e:1f for 1 days 0 hrs 0 mins 0 secs
lease4-update:
*timestamp* Administrator updated information on the lease of address: *address* to a device with hardware address: *device-id*
Dependent on the arguments of the update command, it may also include the
client-id and lease duration.
Example:
2018-01-06 01:02:03 CET Administrator updated information on the lease of address: 192.0.2.202 to a device
with hardware address: 1a:1b:1c:1d:1e:1f, client-id: 1234567890
lease4-del: Deletes have two forms, one by address and one by identifier
and identifier type:
*timestamp* Administrator deleted the lease for address: *address*
or
*timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*
Currently only a type of @b hw-address (hardware address) is supported.
Examples:
2018-01-06 01:02:03 CET Administrator deleted the lease for address: 192.0.2.202
2018-01-06 01:02:12 CET Administrator deleted a lease for a device identified by: hw-address of 1a:1b:1c:1d:1e:1f
14.4.2.3. DHCPv6 Log Entries
For DHCPv6 the library creates entries based on lease management actions
intercepted by the lease6_select (for new leases), lease6_renew (for
renewed leases) and lease6_rebind (for rebound leases).
An entry is a single string with no embedded end-of-line markers, a
prepended timestamp and has the following sections:
timestamp address duration device-id {relay-info}*
Where:
* timestamp - the current date and time the log entry was written in
"%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).
* address - the leased IPv6 address or prefix given out and whether it
was assigned or renewed.
* duration - the lease lifetime expressed in days (if present), hours,
minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
with the text "infinite duration".
* device-id - the client's DUID and hardware address (if present).
* relay-info - for relayed packets the content of relay agent messages,
remote-id (code 37), subscriber-id (code 38) and interface-id (code
18) options if present. Note that interface-id option, if present,
identifies the whole interface the relay agent received the message
on. This typically translates to a single link in your network, but it
depends on your specific network topology. Nevertheless, this is
useful information to better scope down the location of the device, so
it is being recorded, if present.
For instance (line breaks added for readability, they would not be present
in the log file).
2018-01-06 01:02:03 PST Address:2001:db8:1:: has been assigned for 0 hrs 11 mins 53 secs
to a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e
(from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1,
hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f
In addition to logging lease activity driven by DHCPv6 client traffic, it
also logs entries for the following lease management control channel
commands: lease6-add, lease6-update, and lease6-del. Each entry is a
single string with no embedded end-of-line markers and they will typically
have the following forms:
lease6-add:
*timestamp* Administrator added a lease of address: *address* to a device with DUID: *DUID*
Dependent on the arguments of the add command, it may also include the
hardware address and duration.
Example:
2018-01-06 01:02:03 PST Administrator added a lease of address: 2001:db8::3 to a device with DUID:
1a:1b:1c:1d:1e:1f:20:21:22:23:24 for 1 days 0 hrs 0 mins 0 secs
lease6-update:
*timestamp* Administrator updated information on the lease of address: *address* to a device with DUID: *DUID*
Dependent on the arguments of the update command, it may also include the
hardware address and lease duration.
Example:
2018-01-06 01:02:03 PST Administrator updated information on the lease of address: 2001:db8::3 to a device with
DUID: 1a:1b:1c:1d:1e:1f:20:21:22:23:24, hardware address: 1a:1b:1c:1d:1e:1f
lease6-del: Deletes have two forms, one by address and one by identifier
and identifier type:
*timestamp* Administrator deleted the lease for address: *address*
or
*timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*
Currently only a type of DUID is supported.
Examples:
2018-01-06 01:02:03 PST Administrator deleted the lease for address: 2001:db8::3
2018-01-06 01:02:11 PST Administrator deleted a lease for a device identified by: duid of 1a:1b:1c:1d:1e:1f:20:21:22:23:24
14.4.2.4. Configuring the Forensic Log Hooks
To use this functionality the hook library must be included in the
configuration of the desired DHCP server modules. The legal_log library is
installed alongside the Kea libraries in [kea-install-dir]/lib where
kea-install-dir is determined by the "--prefix" option of the configure
script. It defaults to /usr/local. Assuming the default value then,
configuring kea-dhcp4 to load the legal_log library could be done with the
following Kea4 configuration:
"Dhcp4": {
"hooks-libraries": [
{
"library": "/usr/local/lib/libdhcp_legal_log.so",
"parameters": {
"path": "/var/kea/var",
"base-name": "kea-forensic4"
}
},
...
]
}
To configure it for kea-dhcp6, the commands are simply as shown below:
"Dhcp6": {
"hooks-libraries": [
{
"library": "/usr/local/lib/libdhcp_legal_log.so",
"parameters": {
"path": "/var/kea/var",
"base-name": "kea-forensic6"
}
},
...
]
}
Two Hook Library parameters are supported:
* path - the directory in which the forensic file(s) will be written.
The default value is [prefix]/kea/var. The directory must exist.
* base-name - an arbitrary value which is used in conjunction with the
current system date to form the current forensic file name. It
defaults to kea-legal.
If it is desired to restrict forensic logging to certain subnets, the
"legal-logging" boolean parameter can be specified within a user context
of these subnets. For example:
"Dhcpv4" {
"subnet4": [
{
"subnet": "192.0.2.0/24",
"pools": [
{
"pool": "192.0.2.1 - 192.0.2.200"
}
],
"user-context": {
"legal-logging": false
}
}
]
}
disables legal logging for the subnet "192.0.2.0/24". If this parameter is
not specified, it defaults to 'true', which enables legal logging for the
subnet.
The following example demonstrates how to selectively disable legal
logging for an IPv6 subnet.
"Dhcpv6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
"user-context": {
"legal-logging": false
}
}
]
}
See Section 8.11, "User contexts in IPv4" and Section 9.14, "User contexts
in IPv6" to learn more about user contexts in Kea configuration.
14.4.2.5. Database backend
Log entries can be inserted into a database when Kea is configured with
database backend support: a table named 'logs' is used with a timestamp
(timeuuid for Cassandra CQL) generated by the database software and a text
log with the same format than for files without the timestamp.
Please refer to Section 4.3.2, "MySQL" for MySQL, to Section 4.3.3,
"PostgreSQL" for PostgreSQL or to Section 4.3.4, "CQL (Cassandra)" for
Cassandra CQL. Scripts are in path-to-kea/share/kea/legal_log/scripts
directory, for instance the PostgreSQL create schema command is:
$ psql -d database-name -U user-name -f path-to-kea/share/kea/legal_log/scripts/pgsql/legldb_create.pgsql
Password for user user-name:
START TRANSACTION
CREATE TABLE
CREATE INDEX
CREATE TABLE
INSERT 0 1
COMMIT
$
Configuration parameters are extended by standard lease database
parameters as defined in Section 8.2.2.2, "Lease Database Configuration".
The "type" parameter should be "mysql", "postgresql", "cql" or be
"logfile". When it is absent or set to "logfile" files are used.
This database feature is experimental and will be likely improved, for
instance to add an address / prefix index (currently the only index is the
timestamp). No specific tools is provided to operate the database but
standard tools are applicable, for instance to dump the logs table from a
CQL database:
$ echo 'SELECT dateOf(timeuuid), log FROM logs;' | cqlsh -k database-name
system.dateof(timeuuid) | log
---------------------------------+---------------------------------------
2018-01-06 01:02:03.227000+0000 | Address: 192.2.1.100 has been renewed ...
...
(12 rows)
$
14.4.3. flex_id: Flexible Identifiers for Host Reservations
This section describes a hook application dedicated to generate flexible
identifiers for host reservation. Kea software provides a way to handle
host reservations that include addresses, prefixes, options, client
classes and other features. The reservation can be based on hardware
address, DUID, circuit-id or client-id in DHCPv4 and using hardware
address or DUID in DHCPv6. However, there are sometimes scenarios where
the reservation is more complex, e.g. uses other options that mentioned
above, uses part of specific options or perhaps even a combination of
several options and fields to uniquely identify a client. Those scenarios
are addressed by the Flexible Identifiers hook application.
Currently this library is only available to ISC customers with a support
contract.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
The library allows for defining an expression, using notation initially
used for client classification only. See Section 13.3, "Using Expressions
In Classification" for detailed description of the syntax available. One
notable difference is that for client classification the expression
currently has to evaluate to either true or false, while the flexible
identifier expression is expected to evaluate to a string that will be
used as identifier. It is a valid case for the expression to evaluate to
empty string (e.g. in cases where a client does not sent specific
options). This expression is then evaluated for each incoming packet. This
evaluation generates an identifier that is used to identify the client. In
particular, there may be host reservations that are tied to specific
values of the flexible identifier.
The library can be loaded in similar way as other hook libraries. It takes
a mandatory parameter identifier-expression and optional boolean parameter
replace-client-id:
"Dhcp6": {
"hooks-libraries": [
{
"library": "/path/libdhcp_flex_id.so",
"parameters": {
"identifier-expression": "expression",
"replace-client-id": "false"
}
},
...
]
}
The flexible identifier library supports both DHCPv4 and DHCPv6.
EXAMPLE: Let's consider a case of an IPv6 network that has an independent
interface for each of the connected customers. Customers are able to plug
in whatever device they want, so any type of identifier (e.g. a client-id)
is unreliable. Therefore the operator may decide to use an option inserted
by a relay agent to differentiate between clients. In this particular
deployment, the operator verified that the interface-id is unique for each
customer facing interface. Therefore it is suitable for usage as
reservation. However, only the first 6 bytes of the interface-id are
interesting, because remaining bytes are either randomly changed or not
unique between devices. Therefore the customer decided to use first 6
bytes of the interface-id option inserted by the relay agent. After adding
"flex-id" host-reservation-identifiers goal can be achieved by using the
following configuration:
"Dhcp6": {
"subnet6": [{ ..., // subnet definition starts here
"reservations": [
"flex-id": "'port1234'", // value of the first 8 bytes of the interface-id
"ip-addresses": [ "2001:db8::1" ]
],
}], // end of subnet definitions
"host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
"hooks-libraries": [
{
"library": "/path/libdhcp_flex_id.so",
"parameters": {
"identifier-expression": "substring(relay6[0].option[18].hex,0,8)"
}
},
...
]
}
NOTE: Care should be taken when adjusting the expression. If the
expression changes, then all the flex-id values may change, possibly
rendering all reservations based on flex-id unusable until they're
manually updated. Therefore it is strongly recommended to start with the
expression and a handful reservations, adjust the expression as needed and
only after it was confirmed the expression does exactly what is expected
out of it go forward with host reservations on any broader scale.
flex-id values in host reservations can be specified in two ways. First,
they can be expressed as hex string, e.g. bar string can be represented as
626174. Alternatively, it can be expressed as quoted value (using double
and single quotes), e.g. "'bar'". The former is more convenient for
printable characters, while hex string values are more convenient for
non-printable characters.
"Dhcp6": {
"subnet6": [{ ..., // subnet definition starts here
"reservations": [
"flex-id": "01:02:03:04:05:06", // value of the first 8 bytes of the interface-id
"ip-addresses": [ "2001:db8::1" ]
],
}], // end of subnet definitions
"host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
"hooks-libraries": [
{
"library": "/path/libdhcp_flex_id.so",
"parameters": {
"identifier-expression": "vendor[4491].option[1026].hex"
}
},
...
]
}
When "replace-client-id" is set to false (which is the default setting),
the flex-id hook library uses evaluated flexible identifier solely for
identifying host reservations, i.e. searching for reservations within a
database. This is a functional equivalent of other identifiers, similar to
hardware address or circuit-id. However, this mode of operation has an
implication that if a client device is replaced, it may cause a conflict
between an existing lease (allocated for old device) and the new lease
being allocated for the new device. The conflict arises because the same
flexible identifier is computed for the replaced device and the server
will try to allocate the same lease. The mismatch between client
identifiers sent by new device and old device causes the server to refuse
this new allocation until the old lease expires. A manifestation of this
problem is dependant on specific expression used as flexible identifier
and is likely to appear if you only use options and other parameters that
are identifying where the device is connected (e.g. circuit-id), rather
than the device identification itself (e.g. MAC address).
The flex-id library offers a way to overcome the problem with lease
conflicts by dynamically replacing client identifier (or DUID in DHCPv6
case) with a value derived from flexible identifier. The server processes
the client's query as if flexible identifier was sent in the client
identifier (or DUID) option. This guarantees that returning client (for
which the same flexible identifier is evaluated) will be assigned the same
lease despite the client identifier and/or MAC address change.
The following is a stub configuration that enables this behavior:
"Dhcp4": {
"hooks-libraries": [
{
"library": "/path/libdhcp_flex_id.so",
"parameters": {
"identifier-expression": "expression",
"replace-client-id": "true"
}
},
...
]
}
In the DHCPv4 case, the value derived from the flexible identifier is
formed by prepending 1 byte with a value of zero to flexible identifier.
In the IPv6 case, it is formed by prepanding two zero bytes before the
flexible identifier.
Note that for this mechanism to take effect, the DHCPv4 server must be
configured to respect the client identifier option value during lease
allocation, i.e. "match-client-id" must be set to true. See
Section 8.2.19, "Using Client Identifier and Hardware Address" for
details. No additional settings are required for DHCPv6.
If "replace-client-id" option is set to true, the value of
"echo-client-id" parameter (that governs whether to send back a client-id
option or not) is ignored.
The Section 14.4.5, "lease_cmds: Lease Commands" section describes
commands used to retrieve, update and delete leases using various
identifiers, e.g. "hw-address", "client-id". The lease_cmds library
doesn't natively support querying for leases by flexible identifier.
However, when "replace-client-id" is set to true, it makes it possible to
query for leases using a value derived from the flexible identifier. In
the DHCPv4 case, the query will look similar to this:
{
"command": "lease4-get",
"arguments": {
"identifier-type": "client-id",
"identifier": "00:54:64:45:66",
"subnet-id": 44
}
}
where hexadecimal value of "54:64:45:66" is a flexible identifier computed
for the client.
In the DHCPv6 case, the corresponding query will look similar to this:
{
"command": "lease6-get",
"arguments": {
"identifier-type": "duid",
"identifier": "00:00:54:64:45:66",
"subnet-id": 10
}
}
14.4.4. host_cmds: Host Commands
This section describes a hook application that offers a number of new
commands used to query and manipulate host reservations. Kea provides a
way to store host reservations in a database. In many larger deployments
it is useful to be able to manage that information while the server is
running. This library provides management commands for adding, querying
and deleting host reservations in a safe way without restarting the
server. In particular, it validates the parameters, so an attempt to
insert incorrect data e.g. add a host with conflicting identifier in the
same subnet will be rejected. Those commands are exposed via command
channel (JSON over unix sockets) and Control Agent (JSON over RESTful
interface). Additional commands and capabilities related to host
reservations will be added in the future.
Currently this library is only available to ISC customers with a support
contract.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
Currently three commands are supported: reservation-add (which adds new
host reservation), reservation-get (which returns existing reservation if
specified criteria are matched) and reservation-del (which attempts to
delete a reservation matching specified criteria). To use commands that
change the reservation information (currently these are reservation-add
and reservation-del, but this rule applies to other commands that may be
implemented in the future), hosts database must be specified (see
hosts-databases description in Section 8.2.3.1, "DHCPv4 Hosts Database
Configuration" and Section 9.2.3.1, "DHCPv6 Hosts Database Configuration")
and it must not operate in read-only mode. If the hosts-databases are not
specified or are running in read-only mode, the host_cmds library will
load, but any attempts to use reservation-add or reservation-del will
fail.
Additional host reservation commands are planned in the future. For a
description of envisaged commands, see Control API Requirements document.
All commands are using JSON syntax. They can be issued either using
control channel (see Chapter 16, Management API) or via Control Agent (see
Chapter 7, Kea Control Agent).
The library can be loaded in similar way as other hook libraries. It does
not take any parameters. It supports both DHCPv4 and DHCPv6 servers.
"Dhcp6": {
"hooks-libraries": [
{
"library": "/path/libdhcp_host_cmds.so"
}
...
]
}
14.4.4.1. reservation-add command
reservation-add allows for the insertion of a new host. It takes a set of
arguments that vary depending on the nature of the host reservation. Any
parameters allowed in the configuration file that pertain to host
reservation are permitted here. For details regarding IPv4 reservations,
see Section 8.3, "Host Reservation in DHCPv4" and Section 9.3, "Host
Reservation in DHCPv6". There is one notable addition. A subnet-id must be
specified. This parameter is mandatory, because reservations specified in
the configuration file are always defined within a subnet, so the subnet
they belong to is clear. This is not the case with reservation-add,
therefore the subnet-id must be specified explicitly. An example command
can be as simple as:
{
"command": "reservation-add",
"arguments": {
"reservation": {
"subnet-id": 1,
"hw-address": "1a:1b:1c:1d:1e:1f",
"ip-address": "192.0.2.202"
}
}
}
but can also take many more parameters, for example:
{
"command": "reservation-add",
"arguments": {
"reservation":
{
"subnet-id":1,
"client-id": "01:0a:0b:0c:0d:0e:0f",
"ip-address": "192.0.2.205",
"next-server": "192.0.2.1",
"server-hostname": "hal9000",
"boot-file-name": "/dev/null",
"option-data": [
{
"name": "domain-name-servers",
"data": "10.1.1.202,10.1.1.203"
}
],
"client-classes": [ "special_snowflake", "office" ]
}
}
}
Here is an example of complex IPv6 reservation:
{
"command": "reservation-add",
"arguments": {
"reservation":
{
"subnet-id":1,
"duid": "01:02:03:04:05:06:07:08:09:0A",
"ip-addresses": [ "2001:db8:1:cafe::1" ],
"prefixes": [ "2001:db8:2:abcd::/64" ],
"hostname": "foo.example.com",
"option-data": [
{
"name": "vendor-opts",
"data": "4491"
},
{
"name": "tftp-servers",
"space": "vendor-4491",
"data": "3000:1::234"
}
]
}
}
}
The command returns a status that indicates either a success (result 0) or
a failure (result 1). Failed command always includes text parameter that
explains the cause of failure. Example results:
{ "result": 0, "text": "Host added." }
Example failure:
{ "result": 1, "text": "Mandatory 'subnet-id' parameter missing." }
As reservation-add is expected to store the host, hosts-databases
parameter must be specified in your configuration and databases must not
run in read-only mode. In the future versions it will be possible to
modify the reservations read from a configuration file. Please contact ISC
if you are interested in this functionality.
14.4.4.2. reservation-get command
reservation-get can be used to query the host database and retrieve
existing reservations. There are two types of parameters this command
supports: (subnet-id, address) or (subnet-id, identifier-type,
identifier). The first type of query is used when the address (either IPv4
or IPv6) is known, but the details of the reservation aren't. One common
use case of this type of query is to find out whether a given address is
reserved or not. The second query uses identifiers. For maximum
flexibility, Kea stores the host identifying information as a pair of
values: type and the actual identifier. Currently supported identifiers
are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but
additional types may be added in the future. If any new identifier types
are defined in the future, reservation-get command will support them
automatically.
An example command for getting a host reservation by (subnet-id, address)
pair looks as follows:
{
"command": "reservation-get",
"arguments": {
"subnet-id": 1,
"ip-address": "192.0.2.202"
}
}
An example query by (subnet-id, identifier-type, identifier) looks as
follows:
{
"command": "reservation-get",
"arguments":
"subnet-id": 4,
"identifier-type": "hw-address",
"identifier": "01:02:03:04:05:06"
}
}
reservation-get typically returns result 0 when the query was conducted
properly. In particular, 0 is returned when the host was not found. If the
query was successful a number of host parameters will be returned. An
example of a query that did not find the host looks as follows:
{ "result": 0, "text": "Host not found." }
An example result returned when the host was found:
{
"arguments": {
"boot-file-name": "bootfile.efi",
"client-classes": [
],
"hostname": "somehost.example.org",
"hw-address": "01:02:03:04:05:06",
"ip-address": "192.0.2.100",
"next-server": "192.0.0.2",
"option-data": [
],
"server-hostname": "server-hostname.example.org"
},
"result": 0,
"text": "Host found."
}
An example result returned when the query was malformed:
{ "result": 1, "text": "No 'ip-address' provided and 'identifier-type'
is either missing or not a string." }
14.4.4.3. reservation-del command
reservation-del can be used to delete a reservation from the host
database. There are two types of parameters this command supports:
(subnet-id, address) or (subnet-id, identifier-type, identifier). The
first type of query is used when the address (either IPv4 or IPv6) is
known, but the details of the reservation aren't. One common use case of
this type of query is to remove a reservation (e.g. you want a specific
address to no longer be reserved). The second query uses identifiers. For
maximum flexibility, Kea stores the host identifying information as a pair
of values: type and the actual identifier. Currently supported identifiers
are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but
additional types may be added in the future. If any new identifier types
are defined in the future, reservation-get command will support them
automatically.
An example command for deleting a host reservation by (subnet-id, address)
pair looks as follows:
{
"command": "reservation-del",
"arguments": {
"subnet-id": 1,
"ip-address": "192.0.2.202"
}
}
An example deletion by (subnet-id, identifier-type, identifier) looks as
follows:
{
"command": "reservation-del",
"arguments":
"subnet-id": 4,
"identifier-type": "hw-address",
"identifier": "01:02:03:04:05:06"
}
}
reservation-del returns result 0 when the host deletion was successful or
1 if it was not. A descriptive text is provided in case of error. Example
results look as follows:
{
"result": 1,
"text": "Host not deleted (not found)."
}
{
"result": 0,
"text": "Host deleted."
}
{
"result": 1,
"text": "Unable to delete a host because there is no hosts-database
configured."
}
14.4.5. lease_cmds: Lease Commands
This section describes the hook library that offers a number of new
commands used to manage leases. Kea provides a way to store lease
information in several backends (memfile, MySQL, PostgreSQL and
Cassandra). This library provides a unified interface that can manipulate
leases in an unified, safe way. In particular, it allows things previously
impossible: manipulate leases in memfile while Kea is running, sanity
check changes, check lease existence and remove all leases belonging to
specific subnet. It can also catch more obscure errors, like adding a
lease with subnet-id that does not exist in the configuration or
configuring a lease to use an address that is outside of the subnet to
which it is supposed to belong.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
There are many use cases when an administrative command may be useful:
during migration between servers (possibly even between different
vendors), when a certain network is being retired, when a device has been
disconnected and the sysadmin knows for sure that it will not be coming
back. The "get" queries may be useful for automating certain management
and monitoring tasks. They can also act as preparatory steps for lease
updates and removals.
This library provides the following commands:
* lease4-add - adds new IPv4 lease;
* lease6-add - adds new IPv6 lease;
* lease4-get - checks if an IPv4 lease with the specified parameters
exists and returns it if it does;
* lease6-get - checks if an IPv6 lease with the specified parameters
exists and returns it if it does;
* lease4-get-all - returns all IPv4 leases or IPv4 leases for specified
subnets;
* lease6-get-all - returns all IPv6 leases or IPv6 leases for specified
subnets;
* lease4-del - attempts to delete an IPv4 lease with the specified
parameters;
* lease6-del - attempts to delete an IPv6 lease with the specified
parameters;
* lease4-update - updates an IPv4 lease;
* lease6-update - updates an IPv6 lease;
* lease4-wipe - removes all leases from a specific IPv4 subnet or all
subnets;
* lease6-wipe - removes all leases from a specific IPv6 subnet or all
subnets;
Lease commands library is part of the open source code and is available to
every Kea user.
All commands are using JSON syntax. They can be issued either using
control channel (see Chapter 16, Management API) or via Control Agent (see
Chapter 7, Kea Control Agent).
The library can be loaded in the same way as other hook libraries. It does
not take any parameters. It supports both DHCPv4 and DHCPv6 servers.
"Dhcp6": {
"hooks-libraries": [
{
"library": "/path/libdhcp_lease_cmds.so"
}
...
]
}
14.4.5.1. lease4-add, lease6-add commands
lease4-add and lease6-add commands allow for the creation of a new lease.
Typically Kea creates a lease on its own, when it first sees a new device.
However, sometimes it may be convenient to create the lease
administratively. The lease4-add command requires at least three
parameters: an IPv4 address, a subnet-id and an identifier: hardware (MAC)
address. The simplest successful call might look as follows:
{
"command": "lease4-add",
"arguments": {
"subnet-id": 44,
"ip-address": "192.0.2.202",
"hw-address": "1a:1b:1c:1d:1e:1f"
}
}
lease6-add command requires four parameters: an IPv6 address, a subnet-id,
and IAID value (identity association identifier, a value sent by clients)
and a DUID:
{
"command": "lease6-add",
"arguments": {
"subnet-id": 66,
"ip-address": "2001:db8::3",
"duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
"iaid": 1234
}
}
lease6-add can be also used to add leases for IPv6 prefixes. In this case
there are two parameters that must be specified: type (set to value of
"IA_PD") and a prefix length. The actual prefix is set using ip-address
field. For example, to configure a lease for prefix 2001:db8:abcd::/48,
the following command can be used:
{
"command": "lease6-add",
"arguments": {
"subnet-id": 66,
"type": "IA_PD",
"ip-address": "2001:db8:abcd::",
"prefix-len": 48,
"duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
"iaid": 1234
}
}
The commands can take a number of additional optional parameters:
* valid-lft - specifies the lifetime of the lease, expressed in seconds.
If not specified, the value configured in the subnet related to
specified subnet-id is used.
* expire - timestamp of the lease expiration time, expressed in unix
format (seconds since 1 Jan 1970). If not specified, the default value
is now + valid lifetime.
* fqdn-fwd - specifies whether the lease should be marked as if forward
DNS update was conducted. Note this only affects the lease parameter
and the actual DNS update will not be conducted at the lease insertion
time. If configured, a DNS update to remove the A or AAAA records will
be conducted when the lease is removed due to expiration or being
released by a client. If not specified, the default value is false.
Hostname parameter must be specified in fqdn-fwd is set to true.
* fqdn-rev - specifies whether the lease should be marked as if reverse
DNS update was conducted. Note this only affects the lease parameter
and the actual DNS update will not be conducted at the lease insertion
time. If configured, a DNS update to remove the PTR record will be
conducted when the lease is removed due to expiration or being
released by a client. If not specified, the default value is false.
Hostname parameter must be specified in fqdn-fwd is set to true.
* hostname - specifies the hostname to be associated with this lease.
Its value must be non-empty if either fqdn-fwd or fwdn-rev are set to
true. If not specified, the default value is an empty string.
* hw-address - hardware (MAC) address can be optionally specified for
IPv6 lease. It is mandatory parameter for IPv4 lease.
* client-id - client identifier is an optional parameter that can be
specified for IPv4 lease.
* preferred-lft - Preferred lifetime is an optional parameter for IPv6
leases. If not specified, the value configured for the subnet
corresponding to the specified subnet-id is used. This parameter is
not used in IPv4.
Here's an example of more complex lease addition:
{
"command": "lease6-add",
"arguments": {
"subnet-id": 66,
"ip-address": "2001:db8::3",
"duid": "01:02:03:04:05:06:07:08",
"iaid": 1234,
"hw-address": "1a:1b:1c:1d:1e:1f",
"preferred-lft": 500,
"valid-lft": 1000,
"expire": 12345678,
"fqdn-fwd": true,
"fqdn-rev": true,
"hostname": "urania.example.org"
}
}
The command returns a status that indicates either a success (result 0) or
a failure (result 1). Failed command always includes text parameter that
explains the cause of failure. Example results:
{ "result": 0, "text": "Lease added." }
Example failure:
{ "result": 1, "text": "missing parameter 'ip-address' (<string>:3:19)" }
14.4.5.1.1. lease4-get, lease6-get commands
lease4-get or lease6-get can be used to query the lease database and
retrieve existing leases. There are two types of parameters the lease4-get
supports: (address) or (subnet-id, identifier-type, identifier). There are
two types for lease6-get: (address,type) or (subnet-id, identifier-type,
identifier, IAID, type). The first type of query is used when the address
(either IPv4 or IPv6) is known, but the details of the lease aren't. One
common use case of this type of query is to find out whether a given
address is being used or not. The second query uses identifiers. Currently
supported identifiers for leases are: "hw-address" (IPv4 only),
"client-id" (IPv4 only) and "duid" (IPv6 only).
An example lease4-get command for getting a lease by an IPv4 address looks
as follows:
{
"command": "lease4-get",
"arguments": {
"ip-address": "192.0.2.1"
}
}
An example of the lease6-get query looks as follows:
{
"command": "lease6-get",
"arguments": {
"ip-address": "2001:db8:1234:ab::",
"type": "IA_PD"
}
}
An example query by "hw-address" for IPv4 lease looks as follows:
{
"command": "lease4-get",
"arguments": {
"identifier-type": "hw-address",
"identifier": "08:08:08:08:08:08",
"subnet-id": 44
}
}
An example query by "client-id" for IPv4 lease looks as follows:
{
"command": "lease4-get",
"arguments": {
"identifier-type": "client-id",
"identifier": "01:01:02:03:04:05:06",
"subnet-id": 44
}
}
An example query by (subnet-id, identifier-type, identifier, iaid, type)
for IPv6 lease looks as follows:
{
"command": "lease4-get",
"arguments": {
"identifier-type": "duid",
"identifier": "08:08:08:08:08:08",
"iaid": 1234567,
"type": "IA_NA",
"subnet-id": 44
}
}
The type is an optional parameter. Supported values are: IA_NA
(non-temporary address) and IA_PD (IPv6 prefix) are supported. If not
specified, IA_NA is assumed.
leaseX-get returns a result that indicates a result of the operation and
lease details, if found. It has one of the following values: 0 (success),
1 (error) or 2 (empty). The empty result means that a query has been
completed properly, but the object (a lease in this case) has not been
found. The lease parameters, if found, are returned as arguments.
An example result returned when the host was found:
{
"arguments": {
"client-id": "42:42:42:42:42:42:42:42",
"cltt": 12345678,
"fqdn-fwd": false,
"fqdn-rev": true,
"hostname": "myhost.example.com.",
"hw-address": "08:08:08:08:08:08",
"ip-address": "192.0.2.1",
"state": 0,
"subnet-id": 44,
"valid-lft": 3600
},
"result": 0,
"text": "IPv4 lease found."
}
14.4.5.1.2. lease4-get-all, lease6-get-all commands
lease4-get-all and lease6-get-all are used to retrieve all IPv4 or IPv6
leases or all leases for the specified set of subnets. All leases are
returned when there are no arguments specified with the command as in the
following example:
{
"command": "lease4-get-all"
}
If the arguments are provided, it is expected that they contain "subnets"
parameter, being a list of subnet identifiers for which the leases should
be returned. For example, in order to retrieve all IPv6 leases belonging
to the subnets with identifiers 1, 2, 3 and 4:
{
"command": "lease6-get-all",
"arguments": {
"subnets": [ 1, 2, 3, 4 ]
}
}
The returned response contains a detailed list of leases in the following
format:
{
"arguments": {
"leases": [
{
"cltt": 12345678,
"duid": "42:42:42:42:42:42:42:42",
"fqdn-fwd": false,
"fqdn-rev": true,
"hostname": "myhost.example.com.",
"hw-address": "08:08:08:08:08:08",
"iaid": 1,
"ip-address": "2001:db8:2::1",
"preferred-lft": 500,
"state": 0,
"subnet-id": 44,
"type": "IA_NA",
"valid-lft": 3600
},
{
"cltt": 12345678,
"duid": "21:21:21:21:21:21:21:21",
"fqdn-fwd": false,
"fqdn-rev": true,
"hostname": "",
"iaid": 1,
"ip-address": "2001:db8:0:0:2::",
"preferred-lft": 500,
"prefix-len": 80,
"state": 0,
"subnet-id": 44,
"type": "IA_PD",
"valid-lft": 3600
}
]
},
"result": 0,
"text": "2 IPv6 lease(s) found."
}
Warning
The lease4-get and lease6-get commands may result in very large responses.
This may have negative impact on the DHCP server responsiveness while the
response is generated and transmitted over the control channel, as the
server imposes no restriction on the number of leases returned as a result
of this command.
14.4.5.1.3. lease4-del, lease6-del commands
leaseX-del can be used to delete a lease from the lease database. There
are two types of parameters this command supports, similar to leaseX-get
commands: (address) for both v4 and v6, (subnet-id, identifier-type,
identifier) for v4 and (subnet-id, identifier-type, identifier, type,
IAID) for v6. The first type of query is used when the address (either
IPv4 or IPv6) is known, but the details of the lease are not. One common
use case of this type of query is to remove a lease (e.g. you want a
specific address to no longer be used, no matter who may use it). The
second query uses identifiers. For maximum flexibility, this interface
uses identifiers as a pair of values: type and the actual identifier.
Currently supported identifiers are "hw-address" (IPv4 only), "client-id"
(IPv4 only) and "duid" (IPv6 only), but additional types may be added in
the future.
An example command for deleting a host reservation by address looks as
follows:
{
"command": "lease4-del",
"arguments": {
"ip-address": "192.0.2.202"
}
}
An example IPv4 lease deletion by "hw-address" looks as follows:
{
"command": "lease4-del",
"arguments": {
"identifier": "08:08:08:08:08:08",
"identifier-type": "hw-address",
"subnet-id": 44
}
}
leaseX-del returns a result that indicates a outcome of the operation. It
has one of the following values: 0 (success), 1 (error) or 3 (empty). The
empty result means that a query has been completed properly, but the
object (a lease in this case) has not been found.
14.4.5.1.4. lease4-update, lease6-update commands
lease4-update and lease6-update commands can be used to update existing
leases. Since all lease database backends are indexed by IP addresses, it
is not possible to update an address. All other fields may be updated. If
an address needs to be changed, please use leaseX-del followed by
leaseX-add commands.
The optional boolean parameter "force-create" specifies if the lease
should be created if it doesn't exist in the database. It defaults to
false, which indicates that the lease is not created if it doesn't exist.
In such case, an error is returned as a result of trying to update a
non-existing lease. If the "force-create" parameter is set to true and the
updated lease doesn't exist, the new lease is created as a result of
receiving the leaseX-update.
An example command updating IPv4 lease looks as follows:
{
"command": "lease4-update",
"arguments": {
"ip-address": "192.0.2.1",
"hostname": "newhostname.example.org",
"hw-address": "1a:1b:1c:1d:1e:1f",
"subnet-id": 44,
"force-create": true
}
}
An example command updating IPv6 lease looks as follows:
{
"command": "lease6-update",
"arguments": {
"ip-address": "2001:db8::1",
"duid": "88:88:88:88:88:88:88:88",
"iaid": 7654321,
"hostname": "newhostname.example.org",
"subnet-id": 66,
"force-create": false
}
}
14.4.5.1.5. lease4-wipe, lease6-wipe commands
lease4-wipe and lease6-wipe are designed to remove all leases associated
with a given subnet. This administrative task is expected to be used when
existing subnet is being retired. Note that the leases are not properly
expired, there are no DNS updates conducted, no log messages and hooks are
not called for leases being removed.
An example of lease4-wipe looks as follows:
{
"command": "lease4-wipe",
"arguments": {
"subnet-id": 44
}
}
An example of lease6-wipe looks as follows:
{
"command": "lease6-wipe",
"arguments": {
"subnet-id": 66
}
}
The commands return a textual description of the number of leases removed
and 0 (success) status code if any leases were removed and 2 (empty) if
there were no leases. Status code 1 (error) may be returned in case the
parameters are incorrect or some other exception is encountered.
The subnet-id 0 has special meaning. It tells Kea to delete leases from
all configured subnets. Also, the subnet-id parameter may be omitted. If
not specified, leases from all subnets are wiped.
Note: not all backends support this command.
14.4.6. subnet_cmds: Subnet Commands
This section describes a hook application that offers a number of new
commands used to query and manipulate subnet and shared network
configurations in Kea. This application is very useful in deployments with
a large number of subnets being managed by the DHCP servers and when the
subnets are frequently updated. The commands offer lightweight approach
for manipulating subnets without a need to fully reconfigure the server
and without affecting existing servers' configurations. An ability to
manage shared networks (listing, retrieving details, adding new ones,
removing existing ones, adding subnets to and removing from shared
networks) is also provided.
Currently this library is only available to ISC customers with a support
contract.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
The following commands are currently supported:
* subnet4-list/subnet6-list: lists all configured subnets
* subnet4-get/subnet6-get: retrieves detailed information about a
specified subnet
* subnet4-add/subnet6-add: adds new subnet into server's configuration
* subnet4-del/subnet6-del: removes a subnet from the server's
configuration
* network4-list/network6-list: lists all configured shared networks
* network4-get/network6-get: retrieves detailed information about
specified shared network
* network4-add/network6-add: adds a new shared network to the server's
configuration
* network4-del/network6-del: removes a shared network from the server's
configuration
* network4-subnet-add/network6-subnet-add: adds existing subnet to
existing shared network
* network4-subnet-del/network6-subnet-del: removes a subnet from
existing shared network and demotes it to a plain subnet.
14.4.6.1. subnet4-list command
This command is used to list all currently configured subnets. The subnets
are returned in a brief form, i.e. a subnet identifier and subnet prefix
is included for each subnet. In order to retrieve the detailed information
about the subnet the subnet4-get should be used.
This command has the simple structure:
{
"command": "subnet4-list"
}
The list of subnets returned as a result of this command is returned in
the following format:
{
"result": 0,
"text": "2 IPv4 subnets found",
"arguments": {
"subnets": [
{
"id": 10,
"subnet": "10.0.0.0/8"
},
{
"id": 100,
"subnet": "192.0.2.0/24"
}
]
}
If no IPv4 subnets are found, an error code is returned along with the
error description.
14.4.6.2. subnet6-list command
This command is used to list all currently configured subnets. The subnets
are returned in a brief form, i.e. a subnet identifier and subnet prefix
is included for each subnet. In order to retrieve the detailed information
about the subnet the subnet6-get should be used.
This command has the simple structure:
{
"command": "subnet6-list"
}
The list of subnets returned as a result of this command is returned in
the following format:
{
"result": 0,
"text": "2 IPv6 subnets found",
"arguments": {
"subnets": [
{
"id": 11,
"subnet": "2001:db8:1::/64"
},
{
"id": 233,
"subnet": "3000::/16"
}
]
}
If no IPv6 subnets are found, an error code is returned along with the
error description.
14.4.6.3. subnet4-get command
This command is used to retrieve detailed information about the specified
subnet. This command usually follows the subnet4-list, which is used to
discover available subnets with their respective subnet identifiers and
prefixes. Any of those parameters can be then used in subnet4-get to fetch
subnet information:
{
"command": "subnet4-get",
"arguments": {
"id": 10
}
}
or
{
"command": "subnet4-get",
"arguments": {
"subnet": "10.0.0.0/8"
}
}
If the subnet exists the response will be similar to this:
{
"result": 0,
"text": "Info about IPv4 subnet 10.0.0.0/8 (id 10) returned",
"arguments": {
"subnets": [
{
"subnet": "10.0.0.0/8",
"id": 1,
"option-data": [
....
]
...
}
]
}
}
14.4.6.4. subnet6-get command
This command is used to retrieve detailed information about the specified
subnet. This command usually follows the subnet6-list, which is used to
discover available subnets with their respective subnet identifiers and
prefixes. Any of those parameters can be then used in subnet6-get to fetch
subnet information:
{
"command": "subnet6-get",
"arguments": {
"id": 11
}
}
or
{
"command": "subnet6-get",
"arguments": {
"subnet": "2001:db8:1::/64"
}
}
If the subnet exists the response will be similar to this:
{
"result": 0,
"text": "Info about IPv6 subnet 2001:db8:1::/64 (id 11) returned",
"arguments": {
"subnets": [
{
"subnet": "2001:db8:1::/64",
"id": 1,
"option-data": [
...
]
....
}
]
}
}
14.4.6.5. subnet4-add
This command is used to create and add new subnet to the existing server
configuration. This operation has no impact on other subnets. The subnet
identifier must be specified and must be unique among all subnets. If the
identifier or a subnet prefix is not unique an error is reported and the
subnet is not added.
The subnet information within this command has the same structure as the
subnet information in the server configuration file with the exception
that static host reservations must not be specified within subnet4-add.
The commands described in Section 14.4.4, "host_cmds: Host Commands"
should be used to add, remove and modify static reservations.
{
"command": "subnet4-add",
"arguments": {
"subnets": [ {
"id": 123,
"subnet": "10.20.30.0/24",
...
} ]
}
}
The response to this command has the following structure:
{
"result": 0,
"text": "IPv4 subnet added",
"arguments": {
"subnets": [
{
"id": 123,
"subnet": "10.20.30.0/24"
}
]
}
}
14.4.6.6. subnet6-add
This command is used to create and add new subnet to the existing server
configuration. This operation has no impact on other subnets. The subnet
identifier must be specified and must be unique among all subnets. If the
identifier or a subnet prefix is not unique an error is reported and the
subnet is not added.
The subnet information within this command has the same structure as the
subnet information in the server configuration file with the exception
that static host reservations must not be specified within subnet6-add.
The commands described in Section 14.4.4, "host_cmds: Host Commands"
should be used to add, remove and modify static reservations.
{
"command": "subnet6-add",
"arguments": {
"subnet6": [ {
"id": 234,
"subnet": "2001:db8:1::/64",
...
} ]
}
}
The response to this command has the following structure:
{
"result": 0,
"text": "IPv6 subnet added",
"arguments": {
"subnet6": [
{
"id": 234,
"subnet": "2001:db8:1::/64"
}
]
}
}
It is recommended, but not mandatory to specify subnet id. If not
specified, Kea will try to assign the next subnet-id value. This automatic
ID value generator is simple. It returns a previously automatically
assigned value increased by 1. This works well, unless you manually create
a subnet with a value bigger than previously used. For example, if you
call subnet4-add five times, each without id, Kea will assign IDs: 1,2,3,4
and 5 and it will work just fine. However, if you try to call subnet4-add
five times, with the first subnet having subnet-id of value 3 and
remaining ones having no subnet-id, it will fail. The first command (with
explicit value) will use subnet-id 3, the second command will create a
subnet with id of 1, the third will use value of 2 and finally the fourth
will have the subnet-id value auto-generated as 3. However, since there is
already a subnet with that id, it will fail.
The general recommendation is to either: never use explicit values (so the
auto-generated values will always work) or always use explicit values (so
the auto-generation is never used). You can mix those two approaches only
if you understand how the internal automatic subnet-id generation works.
14.4.6.7. subnet4-del command
This command is used to remove a subnet from the server's configuration.
This command has no effect on other configured subnets but removing a
subnet has certain implications which the server's administrator should be
aware of.
In most cases the server has assigned some leases to the clients belonging
to the subnet. The server may also be configured with static host
reservations which are associated with this subnet. The current
implementation of the subnet4-del removes neither the leases nor host
reservations associated with a subnet. This is the safest approach because
the server doesn't loose track of leases assigned to the clients from this
subnet. However, removal of the subnet may still cause configuration
errors and conflicts. For example: after removal of the subnet, the server
administrator may add a new subnet with the ID used previously for the
removed subnet. This means that the existing leases and static
reservations will be in conflict with this new subnet. Thus, we recommend
that this command is used with extreme caution.
This command can also be used to completely delete an IPv4 subnet that is
part of a shared network. If you want to simply remove the subnet from a
shared network and keep the subnet configuration, use network4-subnet-del
command instead.
The command has the following structure:
{
"command": "subnet4-del",
"arguments": {
"id": 123
}
}
The example successful response may look like this:
{
"result": 0,
"text": "IPv4 subnet 192.0.2.0/24 (id 123) deleted",
"arguments": {
"subnets": [
{
"id": 123,
"subnet": "192.0.2.0/24"
}
]
}
}
14.4.6.8. subnet6-del command
This command is used to remove a subnet from the server's configuration.
This command has no effect on other configured subnets but removing a
subnet has certain implications which the server's administrator should be
aware of.
In most cases the server has assigned some leases to the clients belonging
to the subnet. The server may also be configured with static host
reservations which are associated with this subnet. The current
implementation of the subnet6-del removes neither the leases nor host
reservations associated with a subnet. This is the safest approach because
the server doesn't loose track of leases assigned to the clients from this
subnet. However, removal of the subnet may still cause configuration
errors and conflicts. For example: after removal of the subnet, the server
administrator may add a new subnet with the ID used previously for the
removed subnet. This means that the existing leases and static
reservations will be in conflict with this new subnet. Thus, we recommend
that this command is used with extreme caution.
This command can also be used to completely delete an IPv6 subnet that is
part of a shared network. If you want to simply remove the subnet from a
shared network and keep the subnet configuration, use network6-subnet-del
command instead.
The command has the following structure:
{
"command": "subnet6-del",
"arguments": {
"id": 234
}
}
The example successful response may look like this:
{
"result": 0,
"text": "IPv6 subnet 2001:db8:1::/64 (id 234) deleted",
"subnets": [
{
"id": 234,
"subnet": "2001:db8:1::/64"
}
]
}
14.4.6.9. network4-list, network6-list commands
These commands are used to retrieve full list of currently configured
shared networks. The list contains only very basic information about each
shared network. If more details are needed, please use network4-get or
network6-get to retrieve all information available. This command does not
require any parameters and its invocation is very simple:
{
"command": "network4-list"
}
An example response for network4-list looks as follows:
{
"arguments": {
"shared-networks": [
{ "name": "floor1" },
{ "name": "office" }
]
},
"result": 0,
"text": "2 IPv4 network(s) found"
}
network6-list follows exactly the same syntax for both the query and the
response.
14.4.6.10. network4-get, network6-get commands
These commands are used to retrieve detailed information about shared
networks, including subnets currently being part of a given network. Both
commands take one mandatory parameter name, which specify the name of
shared network. An example command to retrieve details about IPv4 shared
network with a name "floor13" looks as follows:
{
"command": "network4-get",
"arguments": {
"name": "floor13"
}
}
An example response could look as follows:
{
"result": 0,
"text": "Info about IPv4 shared network 'floor13' returned",
"arguments": {
"shared-networks": [
{
"match-client-id": true,
"name": "floor13",
"option-data": [ ],
"rebind-timer": 90,
"relay": {
"ip-address": "0.0.0.0"
},
"renew-timer": 60,
"reservation-mode": "all",
"subnet4": [
{
"subnet": "192.0.2.0/24",
"id": 5,
// many other subnet specific details here
},
{
"id": 6,
"subnet": "192.0.3.0/31",
// many other subnet specific details here
}
],
"valid-lifetime": 120
}
]
}
}
Note that actual response contains many additional fields that are omitted
here for clarity. The response format is exactly the same as used in
config-get, just is limited to returning shared networks information.
14.4.6.11. network4-add, network6-add commands
These commands are used to add a new shared network. New network has to
have unique name. This command requires one parameter shared-networks,
which is a list and should contain exactly one entry that defines the
network. The only mandatory element for a network is its name. Although it
does not make operational sense, it is allowed to add an empty shared
network that does not have any subnets in it. That is allowed for testing
purposes, but having empty networks (or with only one subnet) is
discouraged in production environments. For details regarding syntax, see
Section 8.4, "Shared networks in DHCPv4" and Section 9.4, "Shared networks
in DHCPv6".
Note
As opposed to parameter inheritance during full new configuration
processing, this command does not fully handle parameter inheritance and
any missing parameters will be filled with default values, rather than
inherited from global scope.
An example that showcases how to add a new IPv4 shared network looks as
follows:
{
"command": "network4-add",
"arguments": {
"shared-networks": [ {
"name": "floor13",
"subnet4": [
{
"id": 100,
"pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
"subnet": "192.0.2.0/24",
"option-data": [
{
"name": "routers",
"data": "192.0.2.1"
}
]
},
{
"id": 101,
"pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
"subnet": "192.0.3.0/24",
"option-data": [
{
"name": "routers",
"data": "192.0.3.1"
}
]
} ]
} ]
}
}
Assuming there was no shared network with a name floor13 and no subnets
with id 100 and 101 previously configured, the command will be successful
and will return the following response:
{
"arguments": {
"shared-networks": [ { "name": "floor13" } ]
},
"result": 0,
"text": "A new IPv4 shared network 'floor13' added"
}
The network6-add uses the same syntax for both the query and the response.
However, there are some parameters that are IPv4-only (e.g.
match-client-id) and some are IPv6-only (e.g. interface-id). The same
applies to subnets within the network.
14.4.6.12. network4-del, network6-del commands
These commands are used to delete existing shared networks. Both commands
take exactly one parameter 'name' that specifies the name of the network
to be removed. An example invocation of network4-del command looks as
follows:
{
"command": "network4-del",
"arguments": {
"name": "floor13"
}
}
Assuming there was such a network configured, the response will look
similar to the following:
{
"arguments": {
"shared-networks": [
{
"name": "floor13"
}
]
},
"result": 0,
"text": "IPv4 shared network 'floor13' deleted"
}
The network6-del command uses exactly the same syntax for both the command
and the response.
If there are any subnets belonging to the shared network being deleted,
they will be demoted to a plain subnet. There is an optional parameter
called subnets-action that, if specified, takes one of two possible
values: keep (which is the default) and delete. It controls whether the
subnets be demoted to plain subnets or removed. An example usage in
network6-del command that deletes the shared network and all subnets in it
could looks like as follows:
{
"command": "network4-del",
"arguments": {
"name": "floor13",
"subnets-action": "delete"
}
}
Alternatively, if you want to completely remove the subnets, you may use
subnet4-del or subnet6-del commands.
14.4.6.13. network4-subnet-add, network6-subnet-add commands
These commands are used to add existing subnets to existing shared
networks. There are several ways to add new shared network. System
administrator can add the whole shared network at once, either by editing
a configuration file or by calling network4-add or network6-add commands
with desired subnets in it. This approach works better for completely new
shared subnets. However, there may be cases when an existing subnet is
running out of addresses and needs to be extended with additional address
space. In other words another subnet has to be added on top of it. For
this scenario, a system administrator can use network4-add or network6-add
and then add existing subnet to this newly created shared network using
network4-subnet-add or network6-subnet-add.
The network4-subnet-add and network6-subnet-add commands take two
parameters: id, which is an integer and specifies subnet-id of existing
subnet to be added to a shared network; and name, which specifies name of
the shared network the subnet will be added to. The subnet must not belong
to any existing network. In case you want to reassign a subnet from one
shared network to another, please use network4-subnet-del or
network6-subnet-del commands first.
An example invocation of network4-subnet-add command looks as follows:
{
"command": "network4-subnet-add",
"arguments": {
"name": "floor13",
"id": 5
}
}
Assuming there is a network named 'floor13', there is a subnet with
subnet-id 5 and it is not a part of existing network, the command will
return a response similar to the following:
{
"result": 0,
"text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor1'"
}
The network6-subnet-add command uses exactly the same syntax for both the
command and the response.
Note
As opposed to parameter inheritance during full new configuration
processing or when adding a new shared network with new subnets, this
command does not fully handle parameter inheritance and any missing
parameters will be filled with default values, rather than inherited from
global scope or from the shared network.
14.4.6.14. network4-subnet-del, network6-subnet-del commands
These commands are used to remove a subnet that is part of existing shared
network and demote it to a plain, stand-alone subnet. If you want to
remove a subnet completely, use subnet4-del or subnet6-del commands
instead. The network4-subnet-del and network6-subnet-del commands take two
parameters: id, which is an integer and specifies subnet-id of existing
subnet to be removed from a shared network; and name, which specifies name
of the shared network the subnet will be removed from.
An example invocation of the network4-subnet-del command looks as follows:
{
"command": "network4-subnet-del",
"arguments": {
"name": "floor13",
"id": 5
}
}
Assuming there was a subnet with subnet-id equal to 5 that was part of a
shared network named 'floor13', the response would look similar to the
following:
{
"result": 0,
"text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
}
The network6-subnet-del command uses exactly the same syntax for both the
command and the response.
14.4.7. ha: High Availability
This section describes the High Availability hooks library, which can be
loaded on a pair of DHCPv4 or DHCPv6 servers to increase reliability of
the DHCP service in case of outage of one of the servers. This library
used to be only available to ISC customers, but is now part of the open
source Kea, available to all users.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
High Availability (HA) of the DHCP service is provided by running multiple
cooperating server instances. If any of these instances becomes
unavailable for whatever reason (DHCP software crash, Control Agent
software crash, power outage, hardware failure), a surviving server
instance can continue providing the reliable service to the clients. Many
DHCP servers implementations include "DHCP Failover" protocol, which most
significant features are: communication between the servers, partner
failure detection and leases synchronization between the servers. However,
the DHCPv4 failover standardization process was never completed at IETF.
The DHCPv6 failover standard (RFC 8156) was published, but it is complex,
difficult to use, has significant operational constraints and is different
than its v4 counterpart. Although it may be useful for some users to use a
"standard" failover protocol, it seems that most of the Kea users are
simply interested in a working solution which guarantees high availability
of the DHCP service. Therefore, Kea HA hook library derives major concepts
from the DHCP Failover protocol but uses its own solutions for
communication, configuration and its own state machine, which greatly
simplifies its implementation and generally better fits into Kea. Also, it
provides the same features in both DHCPv4 and DHCPv6. This document
purposely uses the term "High Availability" rather than "Failover" to
emphasize that it is not the Failover protocol implementation.
The following sections describe the configuration and operation of the Kea
HA hook library.
14.4.7.1. Supported Configurations
The Kea HA hook library supports two configurations also known as HA
modes: load balancing and hot standby. In the load balancing mode, there
are two servers responding to the DHCP requests. The load balancing
function is implemented as described in RFC3074, with each server
responding to 1/2 of received DHCP queries. When one of the servers
allocates a lease for a client, it notifies the partner server over the
control channel (RESTful API), so as the partner can save the lease
information in its own database. If the communication with the partner is
unsuccessful, the DHCP query is dropped and the response is not returned
to the DHCP client. If the lease update is successful, the response is
returned to the DHCP client by the server which has allocated the lease.
By exchanging the lease updates, both servers get a copy of all leases
allocated by the entire HA setup and any of the servers can be switched to
handle the entire DHCP traffic if its partner becomes unavailable.
In the load balancing configuration, one of the servers must be designated
as "primary" and the other server is designated as "secondary".
Functionally, there is no difference between the two during the normal
operation. This distniction is required when the two servers are started
at (nearly) the same time and have to synchronize their lease databases.
The primary server synchronizes the database first. The secondary server
waits for the primary server to complete the lease database
synchronization before it starts the synchronization.
In the hot standby configuration one of the servers is designated as
"primary" and the second server is designated as "secondary". During the
normal operation, the primary server is the only one that responds to the
DHCP requests. The secodary server receives lease updates from the primary
over the control channel. However, it does not respond to any DHCP queries
as long as the primary is running or, more accurately, until the secondary
considers the primary to be offline. When the secondary server detects the
failure of the primary, it starts responding to all DHCP queries.
In the configurations described above, the primary, secondary and standby
are referred to as "active" servers, because they receive lease updates
and can automatically react to the partner's failures by responding to the
DHCP queries which would normally be handled by the partner. The HA hook
library supports another server type (role) - backup server. The use of
the backup servers is optional. They can be used in both load balancing
and hot standby setup, in addition to the active servers. There is no
limit on the number of backup servers in the HA setup. However, the
presence of the backup servers increases latency of the DHCP responses,
because not only do active servers send lease updates to each other, but
also to the backup servers.
14.4.7.2. Clocks on Active Servers
Synchronized clocks are essential for the HA setup to operate reliably.
The servers share lease information via lease updates and during
synchronization of the databases. The lease information includes the time
when the lease has been allocated and when it expires. Some clock skew
between the servers participating the HA setup would usually exist. This
is acceptable as long as the clock skew is relatively low, comparing to
the lease lifetimes. However, if the clock skew becomes too high, the
different notions of time for the lease expiration by different servers
may cause the HA system to malfuction. For example, one server may
consider a valid lease to be expired. As a consequence, the lease
reclamation process may remove a name associated with this lease from the
DNS, even though the lease may later get renewed by a client.
Each active server monitors the clock skew by comparing its current time
with the time returned by its partner in response to the heartbeat
command. This gives a good approximation of the clock skew, although it
doesn't take into account the time between sending the response by the
partner and receiving this response by the server which sent the heartbeat
command. If the clock skew exceeds 30 seconds, a warning log message is
issued. The administrator may correct this problem by synchronizing the
clocks (e.g. using NTP). The servers should notice the clock skew
correction and stop issuing the warning
If the clock skew is not corrected and it exceeds 60 seconds, the HA
service on each of the servers is terminated, i.e. the state machine
enters the terminated state. The servers will continue to respond to the
DHCP clients (as in the load-balancing or hot-standby mode), but will
neither exchange lease updates nor heartbeats and their lease databases
will diverge. In this case, the administrator should synchronize the
clocks and restart the servers.
14.4.7.3. Server States
The DHCP server operating within an HA setup runs a state machine and the
state of the server can be retrieved by its peers using the ha-heartbeat
command sent over the RESTful API. If the partner server doesn't respond
to the ha-heartbeat command longer than configured amount of time, the
communication is considered interrupted and the server may (depending on
the configuration) use additional measures (desribed further in this
document) to verify if the partner is still operating. If it finds that
the partner is not operating, the server transitions to the partner-down
state to handle the entire DHCP traffic directed to the system.
In this case, the surviving server continues to send the ha-heartbeat
command to detect when the partner wakes up. The partner synchronizes the
lease database and when it is finally ready to operate, the surviving
server returns to the normal operation, i.e. load-balancing or hot-standby
state.
The following is the list of all possible states into which the servers
may transition:
* backup - normal operation of the backup server. In this state it
receives lease updates from the active servers.
* hot-standby - normal operation of the active server running in the hot
standby mode. Both primary and standby server are in this state during
their normal operation. The primary server is responding to the DHCP
queries and sends lease updates to the standby server and to the
backup servers, if any backup servers are present.
* load-balancing - normal operation of the active server running in the
load balancing mode. Both primary and secondary server are in this
state during their normal operation. Both servers are responding to
the DHCP queries and send lease updates to each other and to the
backup servers, if any backup servers are present.
* partner-down - an active server transitions to this state after
detecting that its partner (another active server) is offline. The
server doesn't transition to this state if any of the backup servers
is unavailable. In the partner-down state the server responds to all
DHCP queries, so also those queries which are normally handled by the
active server which is now unavailable.
* ready - an active server transitions to this state after synchronizing
its lease database with an active partner. This state is to indicate
to the partner (likely being in the partner-down state that it may
return to the normal operation. When it does, the server being in the
ready state will also start normal operation.
* syncing - an active server transitions to this state to fetch leases
from the active partner and update the local lease database. When it
this state, it issues the dhcp-disable to disable the DHCP service of
the partner from which the leases are fetched. The DHCP servie is
disabled for the maximum time of 60 seconds, after which it is
automatically enabled, in case the syncing partner has died again
failing to re-enable the service. If the synchronization is completed
the syncing server issues the dhcp-enable to re-enable the DHCP
service of the partner. The syncing operation is synchronous. The
server is waiting for an answer from the partner and is not doing
anything else while the leases synchronization takes place. A server
which is configured to not synchronize its database with the partner,
i.e. when the sync-leases configuration parameter is set to false,
will never transition to this state. Instead, it will transition
directly from the waiting to ready state.
* terminated - an active server transitions to this state when the High
Availability hooks library is unable to further provide reliable
service and a manual intervention of the administrator is required to
correct the problem. It is envisaged that various issues with the HA
setup may cause the server to transition to this state in the future.
As of Kea 1.4.0 release, the only issue causing the HA service to
terminate is unacceptably high clock skew between the active servers,
i.e. if the clocks on respective servers are more than 60 seconds
apart. While in this state, the server will continue responding to the
DHCP clients based on the HA mode selected (load balancing or hot
standby), but the lease updates won't be exchanged and the heartbeats
won't be sent. Once a server has entered the "terminated" state it
will remain in this state until it is restarted. The administrator
must correct the issue which caused this situation prior to restarting
the server (e.g. synchronize clocks). Otherwise, the server will
return to the "terminated" state as soon as it finds that the clock
skew is still too high.
* waiting - each started server instance enters this state. The backup
server will transition directly from this state to the backup state.
An active server will send heartbeat to its partner to check its
state. If the partner appears to be unavailable the server will
transition to the partner-down, otherwise it will transition to the
syncing or ready state (depending on the setting of the sync-leases
configuration parameter). If both servers appear to be in the waiting
state (concurrent startup) the primary server will transition to the
next state first. The secondary or standby server will remain in the
waiting state until the primary transitions to the ready state.
Note
Currently, restarting the HA service being in the terminated state
requires restarting the DHCP server or reloading its configuration. In the
future, we will provide a command to restart the HA service.
Whether the server responds to the DHCP queries and which queries it
responds to is a matter of the server's state, if no administrative action
is performed to configure the server otherwise. The following table
provides the default behavior for various states.
The DHCP Server Scopes denotes what group of received DHCP queries the
server responds to in the given state. The in-depth explanation what the
scopes are can be found below.
Table 14.2. Default behavior of the server in various HA states
+------------------------------------------------------------------------+
| State | Server Type | DHCP Service | DHCP Service Scopes |
|----------------+-----------------+--------------+----------------------|
| backup | backup server | disabled | none |
|----------------+-----------------+--------------+----------------------|
| | primary or | | HA_server1 if |
| hot-standby | standby (hot | enabled | primary, none |
| | standby mode) | | otherwise |
|----------------+-----------------+--------------+----------------------|
| | primary or | | HA_server1 or |
| load-balancing | secondary (load | enabled | HA_server2 |
| | balancing mode) | | |
|----------------+-----------------+--------------+----------------------|
| partner-down | active server | enabled | all scopes |
|----------------+-----------------+--------------+----------------------|
| ready | active server | disabled | none |
|----------------+-----------------+--------------+----------------------|
| syncing | active server | disabled | none |
|----------------+-----------------+--------------+----------------------|
| | | | same as in the |
| terminated | active server | enabled | load-balancing or |
| | | | hot-standby state |
|----------------+-----------------+--------------+----------------------|
| waiting | any server | disabled | none |
+------------------------------------------------------------------------+
The DHCP service scopes require some explanation. The HA configuration
must specify a unique name for each server within the HA setup. This
document uses the following convention within provided examples: server1
for a primary server, server2 for the secondary or standby server and
server3 for the backup server. In the real life any names can be used as
long as they remain unique.
In the load balancing mode there are two scopes named after the active
servers: HA_server1 and HA_server2. The DHCP queries load balanced to the
server1 belong to the HA_server1 scope and the queries load balanced to
the server2 belong to the HA_server2 scope. If any of the servers is in
the partner-down state, it is responsible for serving both scopes.
In the hot standby mode, there is only one scope HA_server1 because only
the server1 is responding to the DHCP queries. If that server becomes
unavailable, the server2 becomes responsible for this scope.
The backup servers do not have their own scopes. In some cases they can be
used to respond to the queries belonging to the scopes of the active
servers. Also, a server which is neither in the partner-down state nor in
the normal operation serves no scopes.
The scope names can be used to associate pools, subnets and networks with
certain servers, so as only these servers can allocate addresses or
prefixes from those pools, subnets or network. This is done via the client
classification mechanism (see below).
14.4.7.4. Scope Transition in Partner Down Case
When one of the servers finds that its partner is unavailble, it will
start serving clients from its own scope and the scope of the partner
which is considered unavailable. This is straight forward for the new
clients, i.e. sending DHCPDISCOVER (DHCPv4) or Solicit (DHCPv6), because
those requests are not sent to any particular server. The available server
will respond to all such queries when it is in the partner-down state.
When the client is renewing a lease, it will send its DHCPREQUEST (DHCPv4)
or Renew (DHCPv6) message directly to the server which has allocated the
lease being renewed. Because this server is unavailable, the client will
not get any response. In that case, the client continues to use its lease
and re-tries to renew until the rebind timer (T2) elapses. The client will
now enter the rebinding phase, in which it will send DHCPREQUEST (DHCPv4)
or Rebind (DHCPv6) message to any available server. The surviving server
will receive the rebinding request and will (typically) extend the
lifetime of the lease. The client will continue to contact that new server
to renew its lease as appropriate.
When the other server becomes available, both active servers will
eventually transition to the load-balancing or hot-standby state, in which
they will be responsible for their own scopes. Some clients belonging to
the scope of the started server will be trying to renew their leases via
the surviving server. This server will not respond to them anymore and the
client will eventually transition back to the right server via rebinding
mechanism again.
14.4.7.5. Load Balancing Configuration
The following is the configuration snippet which enables high availability
on the primary server within the load balancing configuration. The same
configuration should be applied on the secondary and the backup server,
with the only difference that the this-server-name should be set to
server2 and server3 on those servers respectively.
{
"Dhcp4": {
...
"hooks-libraries": [
{
"library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
"parameters": { }
},
{
"library": "/usr/lib/hooks/libdhcp_ha.so",
"parameters": {
"high-availability": [ {
"this-server-name": "server1",
"mode": "load-balancing",
"heartbeat-delay": 10000,
"max-response-delay": 10000,
"max-ack-delay": 5000,
"max-unacked-clients": 5,
"peers": [
{
"name": "server1",
"url": "http://192.168.56.33:8080/",
"role": "primary",
"auto-failover": true
},
{
"name": "server2",
"url": "http://192.168.56.66:8080/",
"role": "secondary",
"auto-failover": true
},
{
"name": "server3",
"url": "http://192.168.56.99:8080/",
"role": "backup",
"auto-failover": false
}
]
} ]
}
}
],
"subnet4": [
{
"subnet": "192.0.3.0/24",
"pools": [
{
"pool": "192.0.3.100 - 192.0.3.150",
"client-class": "HA_server1"
},
{
"pool": "192.0.3.200 - 192.0.3.250",
"client-class": "HA_server2"
}
],
"option-data": [
{
"name": "routers",
"data": "192.0.3.1"
}
],
"relay": { "ip-address": "10.1.2.3" }
}
],
...
}
}
Two hook libraries must be loaded to enable HA: libdhcp_lease_cmds.so and
libdhcp_ha.so. The latter provides the implemenation of the HA feature.
The former enables control commands required by HA to fetch and manipulate
leases on the remote servers. In the example provided above, it is assumed
that Kea libraries are installed in the /usr/lib directory. If Kea is not
installed in the /usr directory, the hook libraries locations must be
updated accordingly.
The HA configuration is specified within the scope of the libdhcp_ha.so.
Note that the top level parameter high-availability is a list, even though
it currently contains only one entry. In the future this configuration is
likely to be extended to contain more entries, if the particular server
can participate in more than one HA relationships.
The following are the global parameters which control the server's
behavior with respect to HA:
* this-server-name - is a unique identifier of the server within this HA
setup. It must match with one of the servers specified within peers
list.
* mode - specifies a HA mode of operation. Currently supported modes are
load-balancing and hot-standby.
* heartbeat-delay - specifies a duration in milliseconds between the
last heartbeat (or other command sent to the partner) and sending the
next heartbeat. The heartbeats are sent periodically to gather the
status of the partner and to verify whether the partner is still
operating. The default value of this parameter is 10000 ms.
* max-response-delay - specifies a duration in milliseconds since the
last successful communication with the partner, after which the server
assumes that the communication with the partner is interrupted. This
duration should be greater than the heartbeat-delay. Usually it is a
greater than the duration of multiple heartbeat-delay values. When the
server detects that the communication is interrupted, it may
transition to the partner-down state (when max-unacked-clients is 0)
or trigger failure detection procedure using the values of the two
parameters below. The default value of this parameter is 60000.
* max-ack-delay - is one of the parameters controlling partner failure
detection. When the communication with the partner is interrupted, the
server examines values of the secs field (DHCPv4) or Elapsed Time
option (DHCPv6) which denote how long the DHCP client has been trying
to communicate with the DHCP server. This parameter specifies the
maximum time in milliseconds for the client to try to communicate with
the DHCP server, after which this server assumes that the client
failed to communicate with the DHCP server (is "unacked"). The default
value of this parameter is 10000.
* max-unacked-clients - specifies how many "unacked" clients are allowed
(see max-ack-delay) before this server assumes that the partner is
offline and transitions to the partner-down state. The special value
of 0 is allowed for this parameter which disables failure detection
mechanism. In this case, the server which can't communicate with the
partner over the control channel assumes that the partner server is
down and transitions to the partner-down state immediately. The
default value of this parameter is 10.
The values of max-ack-delay and max-unacked-clients must be selected
carefully, taking into account specifics of the network in which DHCP
servers are operating. Note that the server in question may not respond to
some of the DHCP clients because these clients are not to be serviced by
this server (per administrative policy). The server may also drop
malformed queries from the clients. Therefore, selecting too low value for
the max-unacked-clients may result in transitioning to the partner-down
state even though the partner is still operating. On the other hand,
selecting too high value may result in never transitioning to the
partner-down state if the DHCP traffic in the network is very low (e.g.
night time), because the number of distinct clients trying to communicate
with the server could be lower than max-unacked-clients.
In some cases it may be useful to disable the failure detection mechanism
altogether, if the servers are located very close to each other and the
network partitioning is unlikely, i.e. failure to respond to heartbeats is
only possible when the partner is offline. In such cases, set the
max-unacked-clients to 0.
The peers parameter contains a list of servers within this HA setup. In
this configuration it must contain at least one primary and one secondary
server. It may also contain unlimited number of backup servers. In this
example there is one backup server which receives lease updates from the
active servers.
There are the following parameters specified for each of the peers within
this list:
* name - specifies unique name for the server.
* url - specifies URL to be used to contact this server over the control
channel. Other servers use this URL to send control commands to that
server.
* role - denotes the role of the server in the HA setup. The following
roles are supported in the load balancing configuration: primary,
secondary and backup. There must be exactly one primary and one
secondary server in the load balancing setup.
* auto-failover - a boolean value which denotes whether the server
detecting a partner's failure should automatically start serving
partner's clients. The default value of this parameter is true.
In our example configuration, both active servers can allocate leases from
the subnet "192.0.3.0/24". This subnet contains two address pools:
"192.0.3.100 - 192.0.3.150" and "192.0.3.200 - 192.0.3.250", which are
associated with HA servers scopes using client classification. When the
server1 processes a DHCP query it will use the first pool for the lease
allocation. Conversely, when the server2 is processing the DHCP query it
will use the second pool. When any of the servers is in the partner-down
state, it can serve leases from both pools and it will select the pool
which is appropriate for the received query. In other words, if the query
would normally be processed by the server2, but this server is not
available, the server1 will allocate the lease from the pool of
"192.0.3.200 - 192.0.3.250".
14.4.7.6. Load Balancing with Advanced Classification
In the previous section we have provided an example which demonstrated the
load balancing configuration with the client classification limited to the
use of HA_server1 and HA_server2 classes, which are dynamically assigned
to the received DHCP queries. In many cases it will be required to use HA
in deployments which already use some client classification.
Suppose there is a system which classifies devices into two groups: phones
and laptops, based on some classification criteria specified in Kea
configuration file. Both types of devices are allocated leases from
different address pools. Introducing HA in the load balancing mode is
expected to result in further split of each of those pools, so as each of
the servers can allocate leases for some part of the phones and part of
the laptops. This requires that each of the existing pools should be split
between the HA_server1 and HA_server2, so we end up with the following
classes:
* phones_server1
* laptops_server1
* phones_server2
* laptops_server2
The corresponding server configuration using advanced classification (and
member expression) is provided below. For brevity the HA hook library
configuration has been removed from this example.
{
"Dhcp4": {
"client-classes": [
{
"name": "phones",
"test": "substring(option[60].hex,0,6) == 'Aastra'",
},
{
"name": "laptops",
"test": "not member('phones')"
},
{
"name": "phones_server1",
"test": "member('phones') and member('HA_server1')"
},
{
"name": "phones_server2",
"test": "member('phones') and member('HA_server2')"
},
{
"name": "laptops_server1",
"test": "member('laptops') and member('HA_server1')"
},
{
"name": "laptops_server2",
"test": "member('laptops') and member('HA_server2')"
}
],
"hooks-libraries": [
{
"library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
"parameters": { }
},
{
"library": "/usr/lib/hooks/libdhcp_ha.so",
"parameters": {
"high-availability": [ {
...
} ]
}
}
],
"subnet4": [
{
"subnet": "192.0.3.0/24",
"pools": [
{
"pool": "192.0.3.100 - 192.0.3.125",
"client-class": "phones_server1"
},
{
"pool": "192.0.3.126 - 192.0.3.150",
"client-class": "laptops_server1"
},
{
"pool": "192.0.3.200 - 192.0.3.225",
"client-class": "phones_server2"
},
{
"pool": "192.0.3.226 - 192.0.3.250",
"client-class": "laptops_server2"
}
],
"option-data": [
{
"name": "routers",
"data": "192.0.3.1"
}
],
"relay": { "ip-address": "10.1.2.3" }
}
],
...
}
}
The configuration provided above splits the address range into four pools.
Two pools are dedicated to server1 and two are dedicated for server2. Each
server can assign leases to both phones and laptops. Both groups of
devices are assigned addresses from different pools. The HA_server1 and
HA_server2 are builtin classes (see Section 13.2, "Builtin Client
Classes") and they don't need to be declared. They are assigned
dynamically by the HA hook library as a result of load balancing
algorithm. The phones_* and laptop_* evaluate to "true" when the query
belongs to a given combination of other classes, e.g. HA_server1 and
phones. The pool will be selected accordingly as a result of such
evaluation.
Consult Chapter 13, Client Classification for details on how to use member
expression and about class dependencies.
14.4.7.7. Hot Standby Configuration
The following is the example configuration of the primary server in the
hot standby configuration:
{
"Dhcp4": {
...
"hooks-libraries": [
{
"library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
"parameters": { }
},
{
"library": "/usr/lib/hooks/libdhcp_ha.so",
"parameters": {
"high-availability": [ {
"this-server-name": "server1",
"mode": "hot-standby",
"heartbeat-delay": 10000,
"max-response-delay": 10000,
"max-ack-delay": 5000,
"max-unacked-clients": 5,
"peers": [
{
"name": "server1",
"url": "http://192.168.56.33:8080/",
"role": "primary",
"auto-failover": true
},
{
"name": "server2",
"url": "http://192.168.56.66:8080/",
"role": "standby",
"auto-failover": true
},
{
"name": "server3",
"url": "http://192.168.56.99:8080/",
"role": "backup",
"auto-failover": false
}
]
} ]
}
}
],
"subnet4": [
{
"subnet": "192.0.3.0/24",
"pools": [
{
"pool": "192.0.3.100 - 192.0.3.250",
"client-class": "HA_server1"
}
],
"option-data": [
{
"name": "routers",
"data": "192.0.3.1"
}
],
"relay": { "ip-address": "10.1.2.3" }
}
],
...
}
}
This configuration is very similar to the load balancing configuration
described Section 14.4.7.5, "Load Balancing Configuration", with a few
notable differences.
The mode is now set to hot-standby, in which only one server is responding
to the DHCP clients. If the primary server is online, the primary server
is responding to all DHCP queries. The standby server takes over the
entire DHCP traffic when it discovers that the primary is unavailable.
In this mode, the non-primary active server is called standby and that's
what the role of the second active server is set to.
Finally, because there is always one server responding to the DHCP
queries, there is only one scope HA_server1 in use within pools
definitions. In fact, the client-class parameter could be removed from
this configuration without harm, because there are no conflicts in lease
allocations by different servers as they do not allocate leases
concurrently. The client-class is left in this example mostly for
demonstration purposes, to highlight the differences between the hot
standby and load balancing mode of operation.
14.4.7.8. Lease Information Sharing
The HA enabled server informs its active partner about allocated or
renewed leases by sending appropriate control commands. The partner
updates the lease information in its own database. When the server starts
up for the first time or recovers after a failure it synchronizes its
lease database with the partner. These two mechanisms guarantee
consistency of the lease information between the servers and allow for
designating one of the servers to handle the entire DHCP traffic in case
the other server becomes unavailable.
In some cases, though, it is desired to disable lease updates and/or
database synchronization between the active servers if the exchange of
information about the allocated leases is performed using some other
mechanism. Kea supports various types of databases to be used as a storage
for leases, e.g. MySQL, Postgres, Cassandra. Those databases include
builtin solutions for data replication which are often used by Kea users
to provide redundancy.
The HA hook library supports such scenarios by allowing to disable lease
updates over the control channel and/or lease database synchronization,
leaving the server to rely on the database replication mechanism. This is
controlled by the two boolean parameters: send-lease-updates and
sync-leases, which values default to true:
{
"Dhcp4": {
...
"hooks-libraries": [
{
"library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
"parameters": { }
},
{
"library": "/usr/lib/hooks/libdhcp_ha.so",
"parameters": {
"high-availability": [ {
"this-server-name": "server1",
"mode": "load-balancing",
"send-lease-updates": false,
"sync-leases": false,
"peers": [
{
"name": "server1",
"url": "http://192.168.56.33:8080/",
"role": "primary"
},
{
"name": "server2",
"url": "http://192.168.56.66:8080/",
"role": "secondary"
}
]
} ]
}
}
],
...
}
In the most typical use case, both parameters are set to the same value,
i.e. both are false if the database replication is in use, or both are
true otherwise. Introducing two separate parameters to control lease
updates and lease database synchronization is aimed at possible special
use cases, e.g. synchronization is performed by copying a lease file
(therefore the sync-leases is set to false), but lease updates should be
conducted as usual (send-lease-updates set to true). It should be noted
that Kea doesn't natively support such use case, but users may develop
their own scripts and tools around Kea to provide such mechanisms. The HA
hooks library configuration is designed to maximize the administration
flexibility.
14.4.7.9. Discussion about Timeouts
In deployments with large number of clients connected to the network,
lease database synchronization after the server failure may be a time
consuming operation. The synchronizing server needs to gather all leases
from the partner which yields a large response over the RESTful interface.
The time required for generating the response and sending it to the
synchronizing server may take from several seconds to tens of seconds. The
default timeout value for such communication is set to 60 seconds.
However, the server administrator may need to extend this timeout if
necessary. The following configuration snippet demonstrates how to extend
this timeout to 90 seconds with the sync-timeout parameter:
{
"Dhcp4": {
...
"hooks-libraries": [
{
"library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
"parameters": { }
},
{
"library": "/usr/lib/hooks/libdhcp_ha.so",
"parameters": {
"high-availability": [ {
"this-server-name": "server1",
"mode": "load-balancing",
"sync-timeout": 90000,
"peers": [
{
"name": "server1",
"url": "http://192.168.56.33:8080/",
"role": "primary"
},
{
"name": "server2",
"url": "http://192.168.56.66:8080/",
"role": "secondary"
}
]
} ]
}
}
],
...
}
It is important to note that extending this value may sometimes be
insufficient to prevent issues with timeouts during lease database
synchronization. The control commands travel via Control Agent, which also
monitors incoming (with synchronizing server) and outgoing (with DHCP
server) connections for timeouts. The DHCP server also monitors the
connection from the Control Agent for timeouts. Those timeouts can't be
currently modified via configuration. Extending these timeouts is only
possible by modifing them in the Kea code and recompiling the server. The
relevant constants are located in the Kea sources:
src/lib/config/timeouts.h.
14.4.7.10. Control Agent Configuration
The Chapter 7, Kea Control Agent describes in detail the Kea deamon which
provides RESTful interface to control Kea servers. The same functionality
is used by High Availability hook library to establish communication
between the HA peers. Therefore, the HA library requires that Control
Agent is started for each DHCP instance within HA setup. If the Control
Agent is not started the peers will not be able to communicate with the
particular DHCP server (even if the DHCP server itself is online) and may
eventually consider this server to be offline.
The following is the example configuration for the CA running on the same
machine as the primary server. This configuration is valid for both load
balancing and hot standby cases presented in previous sections.
{
"Control-agent": {
"http-host": "192.168.56.33",
"http-port": 8080,
"control-sockets": {
"dhcp4": {
"socket-type": "unix",
"socket-name": "/tmp/kea-dhcp4-ctrl.sock"
},
"dhcp6": {
"socket-type": "unix",
"socket-name": "/tmp/kea-dhcp6-ctrl.sock"
}
}
}
}
14.4.7.11. Control Commands for High Availability
Even though the HA hook library is designed to automatically resolve
issues with DHCP service interruptions by redirecting the DHCP traffic to
a surviving server and synchronizing the lease database when required, it
may be useful for the administrator to have control over the server
behavior. In particular, it may be useful be able to trigger lease
database synchronization on demand. It may also be useful to manually set
the HA scopes that are being served.
Note that the backup server can sometimes be used to handle the DHCP
traffic in case if both active servers are down. The backup servers do not
perform failover function automatically. Hence, in order to use the backup
server to respond to the DHCP queries, the server administrator must
enable this function manually.
The following sections describe commands supported by the HA hook library
which are available for the administrator.
14.4.7.11.1. ha-sync command
The ha-sync is issued to instruct the server to synchronize its local
lease database with the selected peer. The server fetches all leases from
the peer and updates those locally stored leases which are older comparing
to those fetched. It also creates new leases when any of those fetched do
not exist in the local database. All leases that are not returned by the
peer but are in the local database are preserved. The database
synchronization is unidirectional, i.e. only the database on the server to
which the command has been sent is updated. In order to synchronize the
peer's database a separate ha-sync has to be issued to that peer.
The database synchronization may be triggered for both active and backup
server type. The ha-sync has the following structure (DHCPv4 server case):
{
"command": "ha-sync",
"service": [ "dhcp4 "],
"arguments": {
"server-name": "server2",
"max-period": 60
}
}
When the server receives this command it first disables the DHCP service
of the server from which it will be fetching leases, i.e. sends
dhcp-disable command to that server. The max-period parameter specifies
the maximum duration (in seconds) for which the DHCP service should be
disabled. If the DHCP service is successfully disabled, the synchronizing
server will fetch leases from the remote server by issuing the
lease4-get-all command. When the lease database synchronization is
complete, the synchronizing server sends the dhcp-enable to the peer to
re-enable its DHCP service.
The max-period value should be sufficiently long to guarantee that it
doesn't elapse before the synchronization is completed. Otherwise, the
DHCP server will automatically enable its DHCP function while the
synchronization is still in progress. If the DHCP server subsequently
allocates any leases during the synchronization, those new (or updated)
leases will not be fetched by the synchronizing server leading to database
inconsistencies.
14.4.7.11.2. ha-scopes command
This command allows for modifying the HA scopes that the server is
serving. Consult Section 14.4.7.5, "Load Balancing Configuration" and
Section 14.4.7.7, "Hot Standby Configuration" to learn what scopes are
available for different HA modes of operation. The ha-scopes command has
the following structure (DHCPv4 server case):
{
"command": "ha-scopes",
"service": [ "dhcp4 "],
"arguments": {
"scopes": [ "HA_server1", "HA_server2" ]
}
}
This command configures the server to handle traffic from both HA_server1
and HA_server2 scopes. In order to disable all scopes specify an empty
list:
{
"command": "ha-scopes",
"service": [ "dhcp4 "],
"arguments": {
"scopes": [ ]
}
}
14.4.8. radius: RADIUS server support
The RADIUS hook library allows Kea to interact with two types of RADIUS
servers: access and accounting. Although the most common DHCP and RADIUS
integration is done on DHCP relay agent level (DHCP clients send DHCP
packets to DHCP relays; relays contact RADIUS server and depending on the
response either send the packet to the DHCP server or drop it), it does
require a DHCP relay hardware to support RADIUS communication. Also, even
if the relay has necessary support it is often not flexible enough to send
and receive additional RADIUS attributes. As such, the alternative looks
more appealing: to extend DHCP server to talk to RADIUS directly. That is
the goal this library intends to fulfill.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
The major feature of the library is the ability to use RADIUS
authorization. When a DHCP packet is received, the Kea server will send
send Access-Request to the RADIUS server and will await a response. The
server will then send back either Access-Accept with specific client
attributes or Access-Reject. There are two cases supported here. First,
the Access-Accept includes Framed-IP-Address (for DHCPv4) or
Framed-IPv6-Address (for DHCPv6), which will be interpreted by Kea as an
instruction to assign that specified IPv4 or IPv6 address. This
effectively means RADIUS can act as address reservation database.
The second case supported is the ability to assign clients to specific
pools based on RADIUS response. In this case RADIUS server sends back
Access-Accept with Framed-Pool (IPv4) or Framed-IPv6-Pool (IPv6). In both
cases, Kea will interpret those attributes as client classes. With the
recent addition of the ability to limit access to pools to specific
classes (see Section 13.7, "Configuring Pools With Class Information"), it
can be used to force client to be assigned a dynamic address from specific
pool. Furthermore, the same mechanism can be used to control what kind of
options the client will get (if there are DHCP options specified for a
particular class).
14.4.8.1. Compilation and Installation of RADIUS Hook
The following section describes how to compile and install the software on
CentOS 7.0. Other systems may differ slightly.
STEP 1: Install dependencies
Several tools are needed to build dependencies and Kea itself. The
following commands should install them:
$ sudo rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
$ sudo yum install gcc-g++ openssl-devel log4cplus-devel wget git
STEP 2: FreeRADIUS installation.
Kea RADIUS hook library uses FreeRadius client library to conduct RADIUS
communication. Unfortunately, the standard 1.1.7 release available from
the project website http://freeradius.org/sub_projects/ has several
serious deficiencies. ISC engineers observed a segmentation fault during
testing. Also, the base version of the library does not offer asynchronous
transmissions, which is essential for effective accounting implementation.
Both of these issues were addressed by ISC engineers. The changes have
been reported to FreeRadius client project. Acceptance of those changes is
outside of ISC responsibilities. Until those are processed, it is strongly
recommended to use FreeRadius client with ISC patches. To and compile this
version, please use the following steps:
$ git clone https://github.com/fxdupont/freeradius-client.git
$ cd freeradius-client/
$ git checkout iscdev
$ ./configure
$ make
$ sudo make install
You may pass additional parameters to configure script, if you need to.
Once installed, the FreeRADIUS client will be installed in /usr/local.
This is the default path where Kea will be looking for it. You may install
it in a different directory. If you choose to do so, make sure you pass
that path to configure script when compiling kea.
STEP 3: Install recent BOOST version
Kea requires reasonably recent Boost version. Unfortunately, the version
available in CentOS 7 is too old. Therefore a newer Boost version is
necessary. Furthermore, CentOS 7 has an old version of g++ compiler that
does not handle latest Boost versions. Fortunately, Boost 1.65 meets both
requirements: is recent enough for Kea and is still able to be compiled
using the g++ 4.8 version in CentOS.
To download and compile Boost 1.65, please use the following commands:
$ wget -nd https://dl.bintray.com/boostorg/release/1.65.1/source/boost_1_65_1.tar.gz
$ tar zxvf boost_1_65_1.tar.gz
$ cd boost_1_65_1/
$ ./bootstrap.sh
$ ./b2 --without-python
$ sudo ./b2 install
Note that b2 script may optionally take extra parameters. One of them
specify the destination path where the sources are to be compiled. Boost
is different compared to other software in the sense that there is no
explicit make install step.
STEP 4: Compile and Install Kea
Obtain Kea sources either by downloading it from git repository or extract
the tarball:
# Use one of those commands to obtain Kea sources:
# Choice 1: get from github
$ git clone https://github.com/isc-projects/kea
# Get a tarball and extract it
$ tar zxvf kea-1.4.0-beta.tar.gz
The next step is to extract premium Kea package that contains Radius
repository into the Kea sources. After the tarball is extracted, the Kea
sources should have a premium/ subdirectory.
$ cd kea
$ tar zxvf ../kea-premium-radius-1.4.0-beta.tar.gz
Once this is done, make sure the kea sources look similar to this:
$ ls -l
total 952
-rw-r--r-- 1 thomson staff 6192 Apr 25 17:38 AUTHORS
-rw-r--r-- 1 thomson staff 29227 Apr 25 17:38 COPYING
-rw-r--r-- 1 thomson staff 360298 Apr 25 20:00 ChangeLog
-rw-r--r-- 1 thomson staff 645 Apr 25 17:38 INSTALL
-rw-r--r-- 1 thomson staff 5015 Apr 25 17:38 Makefile.am
-rw-r--r-- 1 thomson staff 587 Apr 25 17:38 README
drwxr-xr-x 5 thomson staff 170 Apr 26 19:04 compatcheck
-rw-r--r-- 1 thomson staff 62323 Apr 25 17:38 configure.ac
-rw-r--r-- 1 thomson staff 300 Apr 25 17:38 dns++.pc.in
drwxr-xr-x 12 thomson staff 408 Apr 26 19:04 doc
drwxr-xr-x 7 thomson staff 238 Apr 25 17:38 examples
drwxr-xr-x 5 thomson staff 170 Apr 26 19:04 ext
drwxr-xr-x 8 thomson staff 272 Apr 26 19:04 m4macros
drwxr-xr-x 20 thomson staff 680 Apr 26 11:22 premium
drwxr-xr-x 10 thomson staff 340 Apr 26 19:04 src
drwxr-xr-x 14 thomson staff 476 Apr 26 19:04 tools
The next step is to configure Kea. There are several essential steps
necessary here. Running autoreconf -if is necessary to compile premium
package that contains RADIUS. Also, --with-freeradius option is necessary
to tell Kea where the FreeRADIUS client sources can be found. Also, since
the non-standard boost is used, the path to it has to be specified.
If the sources are not from a tarball release, makefiles have to be
regenerated using autoreconf.
$ autoreconf -i
$ ./configure --with-freeradius=/path/to/freeradius --with-boost-include=/path/to/boost --with-boost-lib-dir=/path/to/boost/state/lib
For example, assuming FreeRadius client was installed in the default
directory (/usr/local) and Boost 1.65 sources were compiled in
/home/thomson/devel/boost1_65_1, the configure path should look as
follows:
./configure --with-freeradius=/usr/local \
--with-boost-include=/home/thomson/devel/boost_1_65_1 \
--with-boost-lib-dir=/home/thomson/devel/boost_1_65_1/stage/lib
After some checks, the configure script should print a report similar to
the following:
Kea source configure results:
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Package:
Name: kea
Version: 1.4.0-git
Extended version: 1.4.0-git (git ab3cb8afbb7a4cdaa9cbb279fd783aa126a7912a)
OS Family: Linux
Hooks directory: /usr/local/lib/hooks
Premium hooks: yes
Included Hooks: forensic_log flex_id host_cmds subnet_cmds radius host_cache
C++ Compiler:
CXX: g++ --std=c++11
CXX_VERSION: g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
CXX_STANDARD: 201103
DEFS: -DHAVE_CONFIG_H
CPPFLAGS: -DOS_LINUX -DBOOST_ASIO_HEADER_ONLY
CXXFLAGS: -g -O2
LDFLAGS: -lpthread
KEA_CXXFLAGS: -Wall -Wextra -Wnon-virtual-dtor -Wwrite-strings -Woverloaded-virtual -Wno-sign-compare -pthread -Wno-missing-field-initializers -fPIC
Python:
PYTHON_VERSION: not needed (because kea-shell is disabled)
Boost:
BOOST_VERSION: 1.65.1
BOOST_INCLUDES: -I/home/thomson/devel/boost_1_65_1
BOOST_LIBS: -L/home/thomson/devel/boost_1_65_1/stage/lib -lboost_system
OpenSSL:
CRYPTO_VERSION: OpenSSL 1.0.2k 26 Jan 2017
CRYPTO_CFLAGS:
CRYPTO_INCLUDES:
CRYPTO_LDFLAGS:
CRYPTO_LIBS: -lcrypto
Botan: no
Log4cplus:
LOG4CPLUS_VERSION: 1.1.3
LOG4CPLUS_INCLUDES: -I/usr/include
LOG4CPLUS_LIBS: -L/usr/lib -L/usr/lib64 -llog4cplus
Flex/bison:
FLEX: flex
BISON: bison -y
MySQL:
no
PostgreSQL:
no
Cassandra CQL:
no
Google Test:
no
Google Benchmark:
no
FreeRADIUS client:
FREERADIUS_INCLUDE: -I/usr/local/include
FREERADIUS_LIB: -L/usr/local/lib -lfreeradius-client
FREERADIUS_DICTIONARY: /usr/local/etc/radiusclient/dictionary
Developer:
Enable Debugging: no
Google Tests: no
Valgrind: not found
C++ Code Coverage: no
Logger checks: no
Generate Documentation: no
Parser Generation: no
Kea-shell: no
Please make sure that your compilation has the following:
* radius listed in Included Hooks
* FreeRadius client directories printed and pointing to the right
directories
* Boost version is at least 1.65.1. The versions available in CentOS 7
(1.48 and and 1.53) are too old.
After that compile kea using make. If your system has more than one core,
it is recommended to use -j N option.
$ make -j5
$ sudo make install
14.4.8.2. RADIUS Hook Configuration
The RADIUS Hook is a library that has to be loaded by either DHCPv4 or
DHCPv6 Kea servers. Compared to other available hook libraries, this one
takes many parameters to actually run. For example, this configuration
could be used:
"Dhcp4": {
// Your regular DHCPv4 configuration parameters here.
"hooks-libraries": [
{
// Note that RADIUS requires host-cache for proper operation,
// so that library is loaded as well.
"library": "/usr/local/lib/hooks/libdhcp_host_cache.so"
},
{
"library": "/usr/local/lib/hooks/libdhc_radius.so",
"parameters": {
// Specify where FreeRADIUS dictionary could be located
"dictionary": "/usr/local/etc/freeradius/dictionary",
// Specify which address to use to communicate with RADIUS servers
"bindaddr": "*",
// more RADIUS parameters here
}
} ]
Radius is a complicated environment. As such, it's not really possible to
provide a default configuration that would work out of the box. However,
we do have one example that showcases some of the more common features.
Please see doc/examples/kea4/hooks-radius.json in your Kea sources.
The RADIUS hook library supports the following global configuration flags,
which corresponds to FreeRADIUS client library options:
* bindaddr (default "*") specifies the address to be used by the hook
library in communication with RADIUS servers. The "*" special value
means to leave the kernel to choose it.
* canonical-mac-address (default false) specifies whether MAC addresses
in attributes follows the canonical Radius format (lowercase pairs of
hexadecimal digits separated by '-').
* client-id-pop0 (default false) used with flex-id removes the leading
zero (or pair of zero in DHCPv6) type in client-id (aka duid in
DHCPv6). Implied by client-id-printable.
* client-id-printable (default false) checks if the client-id / duid
content is printable and uses it as it instead of in hexadecimal.
Implies client-id-pop0 and extract-duid as 0 and 255 are not
printable.
* deadtime (default 0) is a mechanism to try not responding servers
after responding servers. Its value specifies the number of seconds
the fact a server did not answer is kept, so 0 disables the mechanism.
As the asynchronous communication does not use locks or atomics it is
not recommended to use this feature with this mode.
* dictionary (default set by configure at build time) is the attribute
and value dictionary. Note it is a critical parameter.
* extract-duid (default true) extracts from RFC 4361 compliant DHCPv4
client-id the embedded duid. Implied by client-id-printable.
* identifier-type4 (default client-id) specifies the identifier type to
build the User-Name attribute. It should be the same than host
identifier and when the flex-id hook library is used the
replace-client-id must be set to true and client-id will be used with
client-id-pop0.
* identifier-type6 (default duid) specifies the identifier type to build
the User-Name attribute. It should be the same than host identifier
and when the flex-id hook librairy is used the replace-client-id must
be set to true and duid will be used with client-id-pop0.
* realm (default "") is the default realm.
* reselect-subnet-address (default false) uses the Kea reserved address
/ RADIUS Framed-IP-Address or Framed-IPv6-Address to reselect subnets
where the address is not in the subnet range.
* reselect-subnet-pool (default false) uses the Kea client-class /
RADIUS Frame-Pool to reselect subnets where no available pool can be
found.
* retries (default 3) is the number of retries before trying the next
server. Note it is not supported for asynchronous communication.
* session-history (default "") is the name of the file providing
persistent storage for accounting session history.
* timeout (default 10) is the number of seconds a response is waited
for.
When reselect-subnet-pool or reselect-subnet-address is set to true at the
reception of RADIUS Access-Accept the selected subnet is checked against
the client-class name or the reserved address and if it does not matched
another subnet is selected among matching subnets.
Two services are supported:
* access - the authentication service
* accounting - the accounting service
Configuration of services is divided into two parts:
* servers that define RADIUS servers the library is expected to contact.
Each server may have the following items specified:
* name which specifies the IP address of the server (it is allowed
to use a name which will be resolved but it is not recommended).
* port (default RADIUS authentication or accounting service) which
specifies the UDP port of the server. Note that the FreeRADIUS
client library by default uses ports 1812 (auth) and 1813 (acct).
Some server implementations use 1645 (auth) ns 1646 (acct). You
may use the "port" parameter to adjust as needed.
* secret which authenticates messages.
There may be up to 8 servers. Note when no server was specified the
service is disabled.
* attributes which define additional attributes that the Kea server will
send to a RADIUS server. The parameter must be identified either by a
name or type. Its value can be specified using one of three possible
ways: data (which defines a plain text value), raw (which defines the
value in hex) or expr (which defines an expression, which will be
evaluated for each incoming packet independently).
* name of the attribute.
* type of the attribute. Type or name is required, and the
attribute must be defined in the dictionary.
* data is the first out of three ways to specify the attribute
content. The data entry is parsed by the FreeRADIUS library so
values defined in the dictionary of the attribute may be used.
* raw is the second out of three way to specify the attribute
content. It specifies the content in hexadecimal. Note it does
not work with integer content attributes (date, integer and IPv4
address), a string content attribute (string. IPv6 address and
IPv6 prefix) is required.
* expr is the last way to specify the attribute content. It
specifies an evaluation expression which must return a not empty
string when evaluated with the DHCP query packet. Currently this
is restricted to the access service.
For example, to specify a single access server available on localhost that
uses "secret" as a secret and tell Kea to send three additional attributes
(Password, Connect-Info and Configuration-Token), the following snipped
could be used:
"parameters": {
// Other RADIUS parameters here
"access": {
// This starts the list of access servers
"servers": [
{
// These are parameters for the first (and only) access server
"server": "127.0.0.1",
"port": 1812,
"secret": "secret"
}
// Additional access servers could be specified here
],
// This define a list of additional attributes Kea will send to each
// access server in Access-Request.
"attributes": [
{
// This attribute is identified by name (must be present in the
// dictionary) and has static value (i.e. the same value will be
// sent to every server for every packet)
"name": "Password",
"data": "mysecretpassword"
},
{
// It's also possible to specify an attribute using its type,
// rather than a name. 77 is Connect-Info. The value is specified
// using hex. Again, this is a static value. It will be sent the
// same for every packet and to every server.
"type": 77,
"raw": "65666a6a71"
},
{
// This example shows how an expression can be used to send dynamic
// value. The expression (see Section 13) may take any value from
// the incoming packet or even its metadata (e.g. the interface
// it was received over from)
"name": "Configuration-Token",
"expr": "pkt.iface"
}
] // End of attributes
} // End of access
// accounting could be specified here.
}
For the RADIUS Hook library to operate properly in DHCPv4, it is necessary
to also load the Host Cache hook library. The reason for this is somewhat
complex. In a typical deployment the DHCP clients send their packets via
DHCP relay which inserts certain Relay Agent Information options, such are
circuit-id or remote-id. The values of those options are then used by the
Kea DHCP server to formulate necessary attributes in the Access-Request
message sent to the RADIUS server. However, once the DHCP client gets its
address, it then renews by sending packets directly to the DHCP server. As
a result, the relays are not able to insert their RAI options and DHCP
server can't send the Access-Request queries to the RADIUS server by using
just the information from incoming packets. Kea needs to keep the
information received during initial Discover/Offer exchanges and later use
it when sending accounting messages.
This mechanism is implemented based on user context in host reservations.
(See Section 14.5, "User contexts" for details about user context). The
host cache mechanism allows to retain the information retrieved by RADIUS
to be stored and later used for sending accounting and access queries to
the RADIUS server. In other words, the host-cache mechanism is mandatory,
unless you don't want the RADIUS communication for messages other than
Discover and the first Request from each client.
14.4.9. host_cache: Caching Host Reservations
Some of the database backends, such as RADIUS, are considered slow and may
take a long time to respond. Since Kea in general is synchronous, the
backend performance directly affects the DHCP performance. To minimize the
impact and improve performance, the Host Cache library provides a way to
cache responses from other hosts. This includes negative caching, i.e. the
ability to remember that there is no client information in the database.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
In principle it can be used with any backend that may introduce
performance degradation (MySQL, PostgreSQL, Cassandra, RADIUS). Host Cache
is required to be loaded for the RADIUS accounting mechanism to work.
Host Cache hook library is currently very simple. It takes only one
optional parameter ("maximum") that defines the maximum number of hosts to
be cached. If not specified the default value of 0 is used, which means
there is no limit. The hook library can be loaded the same way as any
other hook library. For example, this configuration could be used:
"Dhcp4": {
// Your regular DHCPv4 configuration parameters here.
"hooks-libraries": [
{
"library": "/usr/local/lib/hooks/libdhc_host_cache.so",
"parameters": {
// Tells Kea to never cache more than 1000 hosts.
"maximum: "1000"
}
} ]
Once loaded, the Host Cache hook library makes available a number of new
commands. Those commands can be used either over control channel (see
Section 16.2, "Using the Control Channel") or REST API (see Section 7.1,
"Overview"). An example REST API client is described in Section 19.1,
"Overview". The following sections describe the commands available.
14.4.9.1. cache-flush command
This command allows removal of specified number of cached host entries. It
takes one parameter which defines the number of hosts to be removed. An
example usage looks as follows:
{
"command": "cache-flush",
"arguments": 1000
}
This command will remove 1000 hosts. If you want to delete all cached
hosts, please use cache-clear instead. The hosts are stored in FIFO order,
so always the oldest entries are removed.
14.4.9.2. cache-clear command
This command allows removal of all cached host entries. An example usage
looks as follows:
{
"command": "cache-clear"
}
This command will remove all hosts. If you want to delete only certain
number of cached hosts, please use cache-flush instead.
14.4.9.3. cache-write command
In general case the cache content is considered a run-time state and the
server can be shutdown or restarted as usual. The cache will then be
repopulated after restart. However, there are some cases when it is useful
to store contents of the cache. One such case is RADIUS (where the cached
hosts also retain additional cached RADIUS attributes and there is no easy
way to obtain this information again, because renewing clients send their
packet to the DHCP server directly. As a result, packets never go through
relay which doesn't insert relay options, which in turn are in some
deployment to query the RADIUS server). Another use case is when you want
to restart the server and for performance reasons you want it to start
with a hot (populated) cache.
This command allows writing the contents of in-memory cache to a file on
disk. It takes one parameter which defines the filename. An example usage
looks as follows:
{
"command": "cache-write",
"arguments": "/tmp/kea-host-cache.json"
}
This command will store the contents to /tmp/kea-host-cache.json file.
That file can then be loaded with cache-load command or processed by any
other tool that is able to understand JSON format.
14.4.9.4. cache-load command
See previous section for a discussion regarding use cases where it may be
useful to write and load contents of the host cache to disk.
This command allows load the contents of a file on disk into an in-memory
cache. It takes one parameter which defines the filename. An example usage
looks as follows:
{
"command": "cache-load",
"arguments": "/tmp/kea-host-cache.json"
}
This command will store the contents to /tmp/kea-host-cache.json file.
That file can then be loaded with cache-load command or processed by any
other tool that is able to understand JSON format.
14.4.9.5. cache-get command
This command is similar to cache-write, but instead of writing the cache
contents to disk, it returns the contents to whoever sent the command.
This command allows load the contents of a file on disk into an in-memory
cache. It takes one parameter which defines the filename. An example usage
looks as follows:
{
"command": "cache-get"
}
This command will return all the cached hosts. Note the response may be
large.
14.4.9.6. cache-insert command
This command may be used to manually insert a host into the cache. There
are very few use cases when this command could be useful. This command
expects the arguments to follow the usual syntax for specifying host
reservations (see Section 8.3, "Host Reservation in DHCPv4" or
Section 9.3, "Host Reservation in DHCPv6") with one difference: the
subnet-id value must be specified explicitly.
An example command that will insert a IPv4 host into the host cache looks
as follows:
{
"command": "cache-insert",
"arguments": {
"hw-address": "01:02:03:04:05:06",
"subnet-id4": 4,
"subnet-id6": 0,
"ip-address": "192.0.2.100",
"hostname": "somehost.example.org",
"client-classes4": [ ],
"client-classes6": [ ],
"option-data4": [ ],
"option-data6": [ ],
"next-server": "192.0.0.2",
"server-hostname": "server-hostname.example.org",
"boot-file-name": "bootfile.efi",
"host-id": 0
}
}
An example command that will insert IPv6 host into the host cache looks as
follows:
{
"command": "cache-insert",
"arguments": {
"hw-address": "01:02:03:04:05:06",
"subnet-id4": 0,
"subnet-id6": 6,
"ip-addresses": [ "2001:db8::cafe:babe" ],
"prefixes": [ "2001:db8:dead:beef::/64" ],
"hostname": "",
"client-classes4": [ ],
"client-classes6": [ ],
"option-data4": [ ],
"option-data6": [ ],
"next-server": "0.0.0.0",
"server-hostname": "",
"boot-file-name": "",
"host-id": 0
}
}
14.4.9.7. cache-remove command
Sometimes it is useful to remove a single entry from the host cache. A
good use case is a situation where the device is up, Kea already provided
configuration and the host entry is in cache. As a result of
administrative action (e.g. customer hasn't paid their bills or perhaps
been upgraded to better service), the information in the backend (e.g.
MySQL or RADIUS) is being updated. However, since cache is in use, Kea
does not notice the change as the cached values are used. Cache-remove
command can solve this problem by removing cached entry after
administrative changes.
The cache-remove command works similarly to reservation-get command. It
allows querying by two parameters. One of them is either subnet-id4 or
subnet-id6 and the other one is one of: ip-address (may be IPv4 or IPv6
address), hw-address (specifies hardware/MAC address), duid, circuit-id,
client-id or flex-id.
An example command to remove an IPv4 host with reserved address 192.0.2.1
from subnet with a subnet-id 123 looks as follows:
{
"command": "cache-remove",
"arguments": {
"ip-address": "192.0.2.1",
"subnet-id": 123
}
}
Another example that removes IPv6 host identifier by DUID and specific
subnet-id is:
{
"command": "cache-remove",
"arguments": {
"duid": "00:01:ab:cd:f0:a1:c2:d3:e4",
"subnet-id": 123
}
}
14.4.10. stat_cmds: Supplemental Statistics Commands
This library provides additional statistics commands for retrieving lease
statistics from Kea DHCP servers. These commands were added to address an
issue with obtaining accurate lease statistics in deployments running
multiple Kea servers that use shared lease back end. The in-memory
statistics kept by individual servers only track lease changes made by
that server. Thus in a deployment with multiple servers (e.g. two
kea-dhcp6 servers using the same PostgreSQL database for lease storage),
these statistics are incomplete. In Kea 1.4, the MySQL and PostgreSQL back
ends were modified to track lease allocation changes as they occur via
database triggers. Additionally, all four lease back ends were extended to
support retrieving lease statistics for all subnets, a single subnet, or a
range of subnets. Finally, this library was constructed to provide
commands for retrieving these statistics. Additional statistics commands
may be added to this library in future releases.
Note
This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.
The commands currently provided by this library are:
* stat-lease4-get - fetches DHCPv4 lease statistics
* stat-lease6-get - fetches DHCPv6 lease statistics
The Stat commands library is part of the open source code and is available
to every Kea user.
All commands use JSON syntax and can be issued either directly to the
servers via the control channel (see Chapter 16, Management API) or via
Control Agent (see Chapter 7, Kea Control Agent).
This library may be loaded by both kea-dhcp4 and kea-dhcp6 servers. It is
loaded in the same way as other libraries and currently has no parameters:
"Dhcp6": {
"hooks-libraries": [
{
"library": "/path/libdhcp_stat_cmds.so"
}
...
]
}
In a deployment with multiple Kea DHCP servers sharing a common lease
storage, it may be loaded by any or all of the servers. However, one thing
to keep in mind is that a server's response to a stat-lease{4/6}-get
command will only contain data for subnets known to that server. In other
words, if subnet does not appear in a server's configuration, it will not
retrieve statistics for it.
14.4.10.1. stat-lease4-get, stat-lease6-get commands
The stat-lease4-get and stat-lease6-get commands fetch lease statistics
for a range of known subnets. The range of subnets is determined through
the use of optional command input parameters:
* subnet-id - ID of the subnet for which lease statistics should be
fetched. Use this to get statistics for a single subnet. If the subnet
does not exist the command result code will be 3 (i.e.
CONTROL_RESULT_EMPTY).
* subnet-range - A pair of subnet IDs which describe an inclusive range
of subnets for which statistics should be retrieved. Note that fuzzy
values are supported thus allowing for a query for statistics using
approximate ID values. If the range does not include any known
subnets, the command result code will be 3 (i.e.
CONTROL_RESULT_EMPTY).
* first-subnet-id - ID of the first subnet in the range.
* last-subnet-id - ID of the first subnet in the range.
The use of subnet-id and subnet-range are mutually exclusive. If no
parameters are given, the result will contain data for all known subnets.
Note that in configurations with large numbers of subnets, this can be
result in a large response.
The following command would fetch lease statistics for all known subnets
from kea-dhcp4 server:
{
"command": "stat-lease4-get"
}
The following command would fetch lease statistcis for subnet ID 10 from
kea-dhcp6 server:
{
"command": "stat-lease6-get",
"arguments": {
"subnet-id" : 10
}
}
The following command would fetch lease statistcis for all subnets from
subnet ID 10 through 50 from kea-dhcp4 server:
{
"command": "stat-lease4-get",
"arguments": {
"subnet-range" {
"first-subnet-id": 10,
"last-subnet-id": 50,
}
}
}
The response to the either command will contain three elements:
* result - numeric value indicating the outcome of the command where:
* 0 - command was successful
* 1 - an error occurred, an explanation will be the "text" element
* 2 - indicates the fetch found no matching data
* text - an explanation of the command outcome. When the command
succeeds it will contain the command name along with the number of
rows returned.
* arguments - a map containing the data returned by the command as the
element "result-set", which patterned after SQL statement responses:
* columns - a list of text column labels. The columns returned for
DHCPv4 are:
* subnet-id - ID of the subnet
* total-addresses - total number of addresses available for
DHCPv4 management in the subnet. In other words, this is the
sum of all addresses in all the configured pools in the
subnet.
* assigned-addresses - number of addresses in the subnet that
are currently assigned to a client.
* declined-addresses - number of addresses in the subnet that
are currently declined and are thus unavailable for
assignment.
* The columns returned for DHCPv6 are:
* subnet-id - ID of the subnet
* total-nas - number of NA addresses available for DHCPv6
management in the subnet. In other words, this is the sum of
all the NA addresses in the all configured NA pools in the
subnet.
* assigned-nas - number of NA addresses in a the subnet that
are currently assigned to a client.
* declined-nas - number of NA addresses that are currently
declined and are thus unavailable for assignment.
* total-pds - total number of prefixes available of DHCPv6
management in the subnet. In other words, this is the sum of
all prefixes in all the configured prefix pools in the
subnet.
* assigned-pds - number of prefixes in the subnet that are
currently assigned to a client.
* rows - a list of rows, one per subnet ID. Each row contains a
data value for corresponding to and in the same order as each
column listed in "columns" for a given subnet.
* timestamp - textual date and time the data was fetched, expressed
as GMT
The response to a DHCPv4 command might look as follows:
{
"result": 0,
"text": "stat-lease4-get: 2 rows found",
"arguments": {
"result-set": {
"columns": [ "subnet-id", "total-addresses", "assigned-addresses", "declined-addresses" ]
"rows": [
[ 10, 256, 111, 0 ],
[ 20, 4098, 2034, 4 ]
],
"timestamp": "2018-05-04 15:03:37.000000"
}
}
}
The response to a DHCPv6 command might look as follows (subnet 10 has no
prefix pools, subnet 20 has no NA pools, and subnet 30 has both NA and PD
pools):
{
"result": 0,
"text": "stat-lease6-get: 2 rows found",
"arguments": {
"result-set": {
"columns": [ "subnet-id", "total-nas", "assigned-nas", "declined-nas", "total-pds", "assigned-pds" ]
"rows": [
[ 10, 4096, 2400, 3, 0, 0],
[ 20, 0, 0, 0, 1048, 233 ]
[ 30, 256, 60, 0, 1048, 15 ]
],
"timestamp": "2018-05-04 15:03:37.000000"
}
}
}
14.5. User contexts
Hook libraries can have their own configuration parameters. That is
convenient if the parameter applies to the whole library. However,
sometimes it is very useful if certain configuration entities are extended
with additional configuration data. This is where the concept of user
contexts comes in. A sysadmin can define an arbitrary set of data and
attach it to Kea structures, as long as the data is specified as JSON map.
In particular, it is possible to define fields that are integers, strings,
boolean, lists and maps. It is possible to define nested structures of
arbitrary complexity. Kea does not use that data on its own, simply stores
and makes it available for the hook libraries.
Another use case for user contexts may be storing comments and other
information that will be retained by Kea. Regular comments are discarded
when configuration is loaded, but user contexts are retained. This is
useful if you want your comments to survive config-set, config-get
operations for example.
If user context is supported in a given context, the parser translates
"comment" entries into user context with a "comment" entry. The pretty
print of a configuration does the opposite operation and puts "comment"
entries at the beginning of maps as it seems to be the common usage.
As of Kea 1.3, the structures that allow user contexts are pools of all
types (addresses and prefixes) and subnets. Kea 1.4 extended user context
support to the global scope, interfaces config, shared networks, subnets,
client classes, option datas and definitions, host reservations, control
socket, dhcp ddns, loggers and server id. These are supported in both
DHCPv4 and DHCPv6 at the exception of server id which is DHCPv6 only.
Chapter 15. Statistics
Table of Contents
15.1. Statistics Overview
15.2. Statistics Lifecycle
15.3. Commands for Manipulating Statistics
15.3.1. statistic-get command
15.3.2. statistic-reset command
15.3.3. statistic-remove command
15.3.4. statistic-get-all command
15.3.5. statistic-reset-all command
15.3.6. statistic-remove-all command
15.1. Statistics Overview
Both Kea DHCP servers support statistics gathering. A working DHCP server
encounters various events that can cause certain statistics to be
collected. For example, a DHCPv4 server may receive a packet
(pkt4-received statistic increases by one) that after parsing was
identified as a DHCPDISCOVER (pkt4-discover-received). The Server
processed it and decided to send a DHCPOFFER representing its answer
(pkt4-offer-sent and pkt4-sent statistics increase by one). Such events
happen frequently, so it is not uncommon for the statistics to have values
in high thousands. They can serve as an easy and powerful tool for
observing a server's and network's health. For example, if pkt4-received
statistic stops growing, it means that the clients' packets are not
reaching the server.
There are four types of statistics:
* integer - this is the most common type. It is implemented as 64 bit
integer (int64_t in C++), so it can hold any value between -2^63 to
2^63 -1.
* floating point - this type is intended to store floating point
precision. It is implemented as double C++ type.
* duration - this type is intended for recording time periods. It uses
boost::posix_time::time_duration type, which stores hours, minutes,
seconds and microseconds.
* string - this type is intended for recording statistics in textual
form. It uses std::string C++ type.
During normal operation, DHCPv4 and DHCPv6 servers gather statistics. For
a list of DHCPv4 and DHCPv6 statistics, see Section 8.8, "Statistics in
the DHCPv4 Server" and Section 9.12, "Statistics in the DHCPv6 Server",
respectively.
To extract data from the statistics module, the control channel can be
used. See Chapter 16, Management API for details. It is possible to
retrieve a single or all statistics, reset statistics (i.e. set to neutral
value, typically zero) or even remove completely a single or all
statistics. See section Section 15.3, "Commands for Manipulating
Statistics" for a list of statistic oriented commands.
15.2. Statistics Lifecycle
It is useful to understand how the Statistics Manager module works. When
the server starts operation, the manager is empty and does not have any
statistics. When statistic-get-all is executed, an empty list is returned.
Once the server performs an operation that causes a statistic to change,
the related statistic will be created. In the general case, once a
statistic is recorded even once, it is kept in the manager, until
explicitly removed, by statistic-remove or statistic-remove-all being
called or the server is shut down. Per subnet statistics are explicitly
removed when reconfiguration takes place.
Statistics are considered run-time properties, so they are not retained
after server restart.
Removing a statistic that is updated frequently makes little sense as it
will be re-added when the server code next records that statistic. The
statistic-remove and statistic-remove-all commands are intended to remove
statistics that are not expected to be observed in the near future. For
example, a misconfigured device in a network may cause clients to report
duplicate addresses, so the server will report increasing values of
pkt4-decline-received. Once the problem is found and the device is
removed, the system administrator may want to remove the
pkt4-decline-received statistic, so it won't be reported anymore. If a
duplicate address is detected ever again, the server will add this
statistic back.
15.3. Commands for Manipulating Statistics
There are several commands defined that can be used for accessing (-get),
resetting to zero or neutral value (-reset) or even removing a statistic
completely (-remove). The difference between reset and remove is somewhat
subtle. The reset command sets the value of the statistic to zero or
neutral value. After this operation, the statistic will have a value of 0
(integer), 0.0 (float), 0h0m0s0us (duration) or "" (string). When asked
for, a statistic with the values mentioned will be returned. Remove
removes a statistic completely, so the statistic will not be reported
anymore. Please note that the server code may add it back if there's a
reason to record it.
Note
The following sections describe commands that can be sent to the server:
the examples are not fragments of a configuration file. For more
information on sending commands to Kea, see Chapter 16, Management API.
15.3.1. statistic-get command
statistic-get command retrieves a single statistic. It takes a single
string parameter called name that specifies the statistic name. An example
command may look like this:
{
"command": "statistic-get",
"arguments": {
"name": "pkt4-received"
}
}
The server will respond with details of the requested statistic, with
result set to 0 indicating success and the specified statistic as the
value of "arguments" parameter. If the requested statistic is not found,
the response will contain an empty map, i.e. only { } as argument, but the
status code will still be set to success (0).
15.3.2. statistic-reset command
statistic-reset command sets the specified statistic to its neutral value:
0 for integer, 0.0 for float, 0h0m0s0us for time duration and "" for
string type. It takes a single string parameter called name that specifies
the statistic name. An example command may look like this:
{
"command": "statistic-reset",
"arguments": {
"name": "pkt4-received"
}
}
If the specific statistic is found and reset was successful, the server
will respond with a status of 0, indicating success and an empty
parameters field. If an error is encountered (e.g. requested statistic was
not found), the server will return a status code of 1 (error) and the text
field will contain the error description.
15.3.3. statistic-remove command
statistic-remove command attempts to delete a single statistic. It takes a
single string parameter called name that specifies the statistic name. An
example command may look like this:
{
"command": "statistic-remove",
"arguments": {
"name": "pkt4-received"
}
}
If the specific statistic is found and its removal was successful, the
server will respond with a status of 0, indicating success and an empty
parameters field. If an error is encountered (e.g. requested statistic was
not found), the server will return a status code of 1 (error) and the text
field will contain the error description.
15.3.4. statistic-get-all command
statistic-get-all command retrieves all statistics recorded. An example
command may look like this:
{
"command": "statistic-get-all",
"arguments": { }
}
The server will respond with details of all recorded statistics, with
result set to 0 indicating that it iterated over all statistics (even when
the total number of statistics is zero).
15.3.5. statistic-reset-all command
statistic-reset command sets all statistics to their neutral values: 0 for
integer, 0.0 for float, 0h0m0s0us for time duration and "" for string
type. An example command may look like this:
{
"command": "statistic-reset-all",
"arguments": { }
}
If the operation is successful, the server will respond with a status of
0, indicating success and an empty parameters field. If an error is
encountered, the server will return a status code of 1 (error) and the
text field will contain the error description.
15.3.6. statistic-remove-all command
statistic-remove-all command attempts to delete all statistics. An example
command may look like this:
{
"command": "statistic-remove-all",
"arguments": { }
}
If the removal of all statistics was successful, the server will respond
with a status of 0, indicating success and an empty parameters field. If
an error is encountered, the server will return a status code of 1 (error)
and the text field will contain the error description.
Chapter 16. Management API
Table of Contents
16.1. Data Syntax
16.2. Using the Control Channel
16.3. Commands Supported by Both the DHCPv4 and DHCPv6 Servers
16.3.1. build-report
16.3.2. config-get
16.3.3. config-reload
16.3.4. config-test
16.3.5. config-write
16.3.6. leases-reclaim
16.3.7. libreload
16.3.8. list-commands
16.3.9. config-set
16.3.10. shutdown
16.3.11. dhcp-disable
16.3.12. dhcp-enable
16.3.13. version-get
16.4. Commands Supported by Control Agent
A classic approach to daemon configuration assumes that the server's
configuration is stored in configuration files and, when the configuration
is changed, the daemon is restarted. This approach has the significant
disadvantage of introducing periods of downtime, when client traffic is
not handled. Another risk is that if the new configuration is invalid for
whatever reason, the server may refuse to start, which will further extend
the downtime period until the issue is resolved.
To avoid such problems, both the DHCPv4 and DHCPv6 servers include support
for a mechanism that allows on-line reconfiguration without requiring
server shutdown. Both servers can be instructed to open control sockets,
which is a communication channel. The server is able to receive commands
on that channel, act on them and report back status. While the set of
commands in Kea 1.2.0 is limited, the number is expected to grow over
time.
The DHCPv4 and DHCPv6 servers receive commands over the unix domain
sockets. The details how to configure these sockets, see Section 8.9,
"Management API for the DHCPv4 Server" and Section 9.13, "Management API
for the DHCPv6 Server". While it is possible control the servers directly
using unix domain sockets it requires that the controlling client be
running on the same machine as the server. In order to connect remotely
SSH is usually used to connect to the controlled machine.
The network administrators usually prefer using some form of a RESTful API
to control the servers, rather than using unix domain sockets directly.
Therefore, as of Kea 1.2.0 release, Kea includes a new component called
Control Agent (or CA) which exposes a RESTful API to the controlling
clients and can forward commands to the respective Kea services over the
unix domain sockets. The CA configuration has been described in
Section 7.2, "Configuration".
The HTTP requests received by the CA contain the control commands
encapsulated within HTTP requests. Simply speaking, the CA is responsible
for stripping the HTTP layer from the received commands and forwarding the
commands in a JSON format over the unix domain sockets to respective
services. Because the CA receives commands for all services it requires
additional "forwarding" information to be included in the client's
messages. This "forwarding" information is carried within the service
parameter of the received command. If the service parameter is not
included or if the parameter is a blank list the CA will assume that the
control command is targetted at the CA itself and will try to handle it on
its own.
Control connections over both HTTP and unix domain sockets are guarded
with timeouts. The default timeout value is set to 10s and is not
configurable. The timeout configuration will be implemented in the future.
Note
Kea 1.2.0 release and earlier had a limitation of 64kB on the maximum size
of a command and a response sent over the unix domain socket. This
limitation has been removed in Kea 1.3.0 release.
16.1. Data Syntax
Communication over the control channel is conducted using JSON structures.
If configured, Kea will open a socket and listen for incoming connections.
A process connecting to this socket is expected to send JSON commands
structured as follows:
{
"command": "foo",
"service": [ "dhcp4" ]
"arguments": {
"param1": "value1",
"param2": "value2",
...
}
}
The same command sent over the RESTful interface to the CA will have the
following structure.
POST / HTTP/1.1\r\n
Content-Type: application/json\r\n
Content-Length: 147\r\n\r\n
{
"command": "foo",
"service": [ "dhcp4" ]
"arguments": {
"param1": "value1",
"param2": "value2",
...
}
}
command is the name of command to execute and is mandatory. arguments is a
map of parameters required to carry out the given command. The exact
content and format of the map is command specific.
service is a list of the servers at which the control command is
targetted. In the example above, the control command is targetted at the
DHCPv4 server. In most cases, the CA will simply forward this command to
the DHCPv4 server for processing via unix domain socket. Sometimes, the
command including a service value may also be processed by the CA, if the
CA is running a hooks library which handles such command for the given
server. As an example, the hooks library loaded by the CA may perform some
operations on the database (like adding host reservations, modifying
leases etc.). An advantage of performing DHCPv4 specific administrative
operations in the CA rather than forwarding it to the DHCPv4 server is the
ability to perform these operations without disrupting the DHCPv4 service
(DHCPv4 server doesn't have to stop processing DHCP messages to apply
changes to the database). Nevertheless, these situations are rather rare
and, in most cases, when the service parameter contains a name of the
service the commands are simply forwarded by the CA. The forwarded command
includes the service parameter but this parameter is ignored by the
receiving server. This parameter is only meaningful to the CA.
If the command received by the CA does not include a service parameter or
this list is empty, the CA will simply process this message on its own.
For example, the config-get command which doesn't include service
parameter will return Control Agent's own configuration. The config-get
including a service value "dhcp4" will be forwarded to the DHCPv4 server
and will return DHCPv4 server's configuration and so on.
The following list contains a mapping of the values carried within the
service parameter to the servers to which the commands are forwarded:
* dhcp4 - the command is forwarded to the kea-dhcp4 server,
* dhcp6 - the command is forwarded to the kea-dhcp6 server,
* d2 - the command is forwarded to the kea-d2 server.
The server processing the incoming command will send a response of the
form:
{
"result": 0|1|2|3,
"text": "textual description",
"arguments": {
"argument1": "value1",
"argument2": "value2",
...
}
}
result indicates the outcome of the command. A value of 0 means success
while any non-zero value designates an error or at least a failure to
complete the requested action. Currently 1 is used as a generic error, 2
means that a command is not supported and 3 means that the requested
operation was completed, but the requested object was not found.
Additional error codes may be added in the future. For example a well
formed command that requests a subnet that exists in server's
configuration would return result 0. If the server encounters an error
condition, it would return 1. If the command was asking for IPv6 subnet,
but was sent to DHCPv4 server, it would return 2. If the query was asking
for a subnet-id and there is no subnet with such id, the result would be
set to 3.
The text field typically appears when result is non-zero and contains a
description of the error encountered, but it often also appears for
successful outcomes. The exact text is command specific, but in general
uses plain English to describe the outcome of the command. arguments is a
map of additional data values returned by the server which is specific to
the command issued. The map is may be present, but that depends on
specific command.
Note
When sending commands via Control Agent, it is possible to specify
multiple services at which the command is targetted. CA will forward this
command to each service individually. Thus, the CA response to the
controlling client will contain an array of individual responses.
16.2. Using the Control Channel
Kea development team is actively working on providing client applications
which can be used to control the servers. These applications are, however,
in the early stages of development and as of Kea 1.2.0 release have
certain limitations. The easiest way to start interacting with the control
API is to use common Unix/Linux tools such as socat and curl.
In order to control the given Kea service via unix domain socket, use
socat in interactive mode as follows:
$ socat UNIX:/path/to/the/kea/socket -
or in batch mode, include the "ignoreeof" option as shown below to ensure
socat waits long enough for the server to respond:
$ echo "{ some command...}" | socat UNIX:/path/to/the/kea/socket -,ignoreeof
where /path/to/the/kea/socket is the path specified in the
Dhcp4/control-socket/socket-name parameter in the Kea configuration file.
Text passed to socat will be sent to Kea and the responses received from
Kea printed to standard output. This approach communicates with the
specific server directly and bypasses Control Agent.
It is also easy to open UNIX socket programmatically. An example of such a
simplistic client written in C is available in the Kea Developer's Guide,
chapter Control Channel Overview, section Using Control Channel.
In order to use Kea's RESTful API with curl you may use the following:
$ curl -X POST -H "Content-Type: application/json" -d '{ "command": "config-get", "service": [ "dhcp4" ] }' http://ca.example.org:8000/
This assumes that the Control Agent is running on host ca.example.org and
runs RESTful service on port 8000.
16.3. Commands Supported by Both the DHCPv4 and DHCPv6 Servers
16.3.1. build-report
The build-report command returns on the control channel what the command
line -W argument displays, i.e. the embedded content of the config.report
file. This command does not take any parameters.
{
"command": "build-report"
}
16.3.2. config-get
The config-get command retrieves the current configuration used by the
server. This command does not take any parameters. The configuration
returned is roughly equal to the configuration that was loaded using -c
command line option during server start-up or later set using config-set
command. However, there may be certain differences. Comments are not
retained. If the original configuration used file inclusion, the returned
configuration will include all parameters from all the included files.
Note that returned configuration is not redacted, i.e. it will contain
database passwords in plain text if those were specified in the original
configuration. Care should be taken to not expose the command channel to
unprivileged users.
An example command invocation looks like this:
{
"command": "config-get"
}
16.3.3. config-reload
The config-reload command instructs Kea to load again the configuration
file that was used previously. This operation is useful if the
configuration file has been changed by some external sources. For example,
a sysadmin can tweak the configuration file and use this command to force
Kea pick up the changes.
Caution should be taken when mixing this with config-set commands. Kea
remembers the location of the configuration file it was started with. This
configuration can be significantly changed using config-set command. When
config-reload is issued after config-set, Kea will attempt to reload its
original configuration from the file, possibly losing all changes
introduced using config-set or other commands.
config-reload does not take any parameters. An example command invocation
looks like this:
{
"command": "config-reload"
}
16.3.4. config-test
The config-test command instructs the server to check whether the new
configuration supplied in the command's arguments can be loaded. The
supplied configuration is expected to be the full configuration for the
target server along with an optional Logger configuration. As for the -t
command some sanity checks are not performed so it is possible a
configuration which successfully passes this command will still fail in
config-set command or at launch time. The structure of the command is as
follows:
{
"command": "config-test",
"arguments": {
"<server>": {
},
"Logging": {
}
}
}
where <server> is the configuration element name for a given server such
as "Dhcp4" or "Dhcp6". For example:
{
"command": "config-test",
"arguments": {
"Dhcp6": {
:
},
"Logging": {
:
}
}
}
The server's response will contain a numeric code, "result" (0 for
success, non-zero on failure), and a string, "text", describing the
outcome:
{"result": 0, "text": "Configuration seems sane..." }
or
{"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }
16.3.5. config-write
The config-write command instructs Kea server to write its current
configuration to a file on disk. It takes one optional argument called
filename that specifies the name of the file to write configuration to. If
not specified, the name used when starting Kea (passed as -c argument)
will be used. If relative path is specified, Kea will write its files only
in the directory it is running.
An example command invocation looks like this:
{
"command": "config-write",
"arguments": {
"filename": "config-modified-2017-03-15.json"
}
}
16.3.6. leases-reclaim
The leases-reclaim command instructs the server to reclaim all expired
leases immediately. The command has the following JSON syntax:
{
"command": "leases-reclaim",
"arguments": {
"remove": true
}
}
The remove boolean parameter is mandatory and it indicates whether the
reclaimed leases should be removed from the lease database (if true), or
they should be left in the expired-reclaimed state (if false). The latter
facilitates lease affinity, i.e. ability to re-assign expired lease to the
same client which used this lease before. See Section 10.3, "Configuring
Lease Affinity" for the details. Also, see Section 10.1, "Lease
Reclamation" for the general information about the processing of expired
leases (leases reclamation).
16.3.7. libreload
The libreload command will first unload and then load all currently loaded
hook libraries. This is primarily intended to allow one or more hook
libraries to be replaced with newer versions without requiring Kea servers
to be reconfigured or restarted. Note the hook libraries will be passed
the same parameter values (if any) they were passed when originally
loaded.
{
"command": "libreload",
"arguments": { }
}
The server will respond with a result of 0 indicating success, or 1
indicating a failure.
16.3.8. list-commands
The list-commands command retrieves a list of all commands supported by
the server. It does not take any arguments. An example command may look
like this:
{
"command": "list-commands",
"arguments": { }
}
The server will respond with a list of all supported commands. The
arguments element will be a list of strings. Each string will convey one
supported command.
16.3.9. config-set
The config-set command instructs the server to replace its current
configuration with the new configuration supplied in the command's
arguments. The supplied configuration is expected to be the full
configuration for the target server along with an optional Logger
configuration. While optional, the Logger configuration is highly
recommended as without it the server will revert to its default logging
configuration. The structure of the command is as follows:
{
"command": "config-set",
"arguments": {
"<server>": {
},
"Logging": {
}
}
}
where <server> is the configuration element name for a given server such
as "Dhcp4" or "Dhcp6". For example:
{
"command": "config-set",
"arguments": {
"Dhcp6": {
:
},
"Logging": {
:
}
}
}
If the new configuration proves to be invalid the server will retain its
current configuration. Please note that the new configuration is retained
in memory only. If the server is restarted or a configuration reload is
triggered via a signal, the server will use the configuration stored in
its configuration file. The server's response will contain a numeric code,
"result" (0 for success, non-zero on failure), and a string, "text",
describing the outcome:
{"result": 0, "text": "Configuration successful." }
or
{"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }
16.3.10. shutdown
The shutdown command instructs the server to initiate its shutdown
procedure. It is the equivalent of sending a SIGTERM signal to the
process. This command does not take any arguments. An example command may
look like this:
{
"command": "shutdown"
}
The server will respond with a confirmation that the shutdown procedure
has been initiated.
16.3.11. dhcp-disable
The dhcp-disable command globally disables the DHCP service. The server
continues to operate, but it drops all received DHCP messages. This
command is useful when the server's maintenance requires that the server
temporarily stops allocating new leases and renew existing leases. It is
also useful in failover like configurations during a synchronization of
the lease databases at startup or recovery after a failure. The optional
parameter max-period specifies the time in seconds after which the DHCP
service should be automatically re-enabled if the dhcp-enable command is
not sent before this time elapses.
{
"command": "dhcp-disable",
"arguments": {
"max-period": 20
}
}
16.3.12. dhcp-enable
The dhcp-enable command globally enables the DHCP service.
{
"command": "dhcp-enable"
}
16.3.13. version-get
The version-get command returns on the control channel what the command
line -v argument displays with in arguments the extended version, i.e.,
what the command line -V argument displays. This command does not take any
parameters.
{
"command": "version-get"
}
16.4. Commands Supported by Control Agent
The following commands listed in Section 16.3, "Commands Supported by Both
the DHCPv4 and DHCPv6 Servers" are also supported by the Control Agent,
i.e. when the service parameter is blank the commands are handled by the
CA and they relate to the CA process itself:
* build-report
* config-get
* config-test
* config-write
* list-commands
* shutdown
* version-get
Chapter 17. The libdhcp++ Library
Table of Contents
17.1. Interface detection and Socket handling
libdhcp++ is a library written in C++ that handles many DHCP-related
tasks, including:
* DHCPv4 and DHCPv6 packets parsing, manipulation and assembly
* Option parsing, manipulation and assembly
* Network interface detection
* Socket operations such as creation, data transmission and reception
and socket closing.
While this library is currently used by Kea, it is designed to be a
portable, universal library, useful for any kind of DHCP-related software.
17.1. Interface detection and Socket handling
Both the DHCPv4 and DHCPv6 components share network interface detection
routines. Interface detection is currently supported on Linux, all BSD
family (FreeBSD, NetBSD, OpenBSD), Mac OS X and Solaris 11 systems.
DHCPv4 requires special raw socket processing to send and receive packets
from hosts that do not have IPv4 address assigned. Support for this
operation is implemented on Linux, FreeBSD, NetBSD and OpenBSD. It is
likely that DHCPv4 component will not work in certain cases on other
systems.
Chapter 18. Logging
Table of Contents
18.1. Logging Configuration
18.1.1. Loggers
18.1.2. Logging Message Format
18.1.3. Logging During Kea Startup
18.1. Logging Configuration
During its operation Kea may produce many messages. They differ in
severity (some are more important than others) and source (some are
produced by specific components, e.g. hooks). It is useful to understand
which log messages are needed and which are not, and configure your
logging appropriately. For example, debug level messages can be safely
ignored in a typical deployment. They are, however, very useful when
debugging a problem.
The logging system in Kea is configured through the Logging section in
your configuration file. All daemons (e.g. DHCPv4 and DHCPv6 servers) will
use the configuration in the Logging section to see what should be logged
and to where. This allows for sharing identical logging configuration
between daemons.
18.1.1. Loggers
Within Kea, a message is logged through an entity called a "logger".
Different components log messages through different loggers, and each
logger can be configured independently of one another. Some components, in
particular the DHCP server processes, may use multiple loggers to log
messages pertaining to different logical functions of the component. For
example, the DHCPv4 server uses one logger for messages pertaining to
packet reception and transmission, another logger for messages related to
lease allocation and so on. Some of the libraries used by the Kea servers,
e.g. libdhcpsrv, use their own loggers.
Users implementing hooks libraries (code attached to the server at
runtime) are responsible for creating the loggers used by those libraries.
Such loggers should have unique names, different from the logger names
used by Kea. In this way the messages output by the hooks library can be
distinguished from messages issued by the core Kea code. Unique names also
allow the loggers to be configured independently of loggers used by Kea.
Whenever it makes sense, a hook library can use multiple loggers to log
messages pertaining to different logical parts of the library.
In the Logging section of a configuration file you can specify the
configuration for zero or more loggers (including loggers used by the
proprietary hooks libraries). If there are no loggers specified, the code
will use default values: these cause Kea to log messages of INFO severity
or greater to standard output. There is also a small time window after Kea
has been started, but has not yet read its configuration. Logging in this
short period can be controlled using environment variables. For details,
see Section 18.1.3, "Logging During Kea Startup".
The three main elements of a logger configuration are: name (the component
that is generating the messages), the severity (what to log), and the
output_commands (where to log). There is also a debuglevel element, which
is only relevant if debug-level logging has been selected.
18.1.1.1. name (string)
Each logger in the system has a name, the name being that of the component
binary file using it to log messages. For instance, if you want to
configure logging for the DHCPv4 server, you add an entry for a logger
named "kea-dhcp4". This configuration will then be used by the loggers in
the DHCPv4 server, and all the libraries used by it (unless a library
defines its own logger and there is specific logger configuration that
applies to that logger).
When tracking down an issue with the server's operation, use of DEBUG
logging is required to obtain the verbose output needed for problems
diagnosis. However, the high verbosity is likely to overwhelm the logging
system in cases when the server is processing high volume traffic. To
mitigate this problem, use can be made of the fact that Kea uses multiple
loggers for different functional parts of the server and that each of
these can be configured independently. If the user is reasonably confident
that a problem originates in a specific function of the server, or that
the problem is related to the specific type of operation, they may enable
high verbosity only for the relevant logger, so limiting the debug
messages to the required minimum.
The loggers are associated with a particular library or binary of Kea.
However, each library or binary may (and usually does) include multiple
loggers. For example, the DHCPv4 server binary contains separate loggers
for: packet parsing, for dropped packets, for callouts etc.
The loggers form a hierarchy. For each program in Kea, there is a "root"
logger, named after the program (e.g. the root logger for kea-dhcp (the
DHCPv4 server) is named kea-dhcp4. All other loggers are children of this
logger, and are named accordingly, e.g. the the allocation engine in the
DHCPv4 server logs messages using a logger called kea-dhcp4.alloc-engine.
This relationship is important as each child logger derives its default
configuration from its parent root logger. In the typical case, the root
logger configuration is the only logging configuration specified in the
configuration file and so applies to all loggers. If an entry is made for
a given logger, any attributes specified override those of the root
logger, whereas any not specified are inherited from it.
To illustrate this, suppose you are using the DHCPv4 server with the root
logger "kea-dhcp4" logging at the INFO level. In order to enable DEBUG
verbosity for the DHCPv4 packet drops, you must create configuration entry
for the logger called "kea-dhcp4.bad-packets" and specify severity DEBUG
for this logger. All other configuration parameters may be omitted for
this logger if the logger should use the default values specified in the
root logger's configuration.
If there are multiple logger specifications in the configuration that
might match a particular logger, the specification with the more specific
logger name takes precedence. For example, if there are entries for both
"kea-dhcp4" and "kea-dhcp4.dhcpsrv", the DHCPv4 server -- and all
libraries it uses that are not dhcpsrv -- will log messages according to
the configuration in the first entry ("kea-dhcp4").
Currently defined loggers are defined in the following table. The
"Software Package" column of this table specifies whether the particular
loggers belong to the core Kea code (open source Kea binaries and
libraries), or hook libraries (open source or premium).
Table 18.1. List of loggers supported by Kea servers and hooks libraries
shipped with Kea and premium packages
+------------------------------------------------------------------------+
| Logger Name | Software Package | Description |
|-----------------------------+----------------------+-------------------|
| | | The root logger |
| | | for the Control |
| | | Agent exposing |
| | | RESTful control |
| kea-ctrl-agent | core | API. All |
| | | components used |
| | | by the Control |
| | | Agent inherit the |
| | | settings from |
| | | this logger. |
|-----------------------------+----------------------+-------------------|
| | | A logger which |
| | | outputs log |
| | | messages related |
| kea-ctrl-agent.http | core | to receiving, |
| | | parsing and |
| | | sending HTTP |
| | | messages. |
|-----------------------------+----------------------+-------------------|
| | | The root logger |
| | | for the DHCPv4 |
| | | server. All |
| kea-dhcp4 | core | components used |
| | | by the DHCPv4 |
| | | server inherit |
| | | the settings from |
| | | this logger. |
|-----------------------------+----------------------+-------------------|
| | | The root logger |
| | | for the DHCPv6 |
| | | server. All |
| kea-dhcp6 | core | components used |
| | | by the DHCPv6 |
| | | server inherit |
| | | the settings from |
| | | this logger. |
|-----------------------------+----------------------+-------------------|
| | | Used by the lease |
| | | allocation |
| | | engine, which is |
| | | responsible for |
| | | managing leases |
| | | in the lease |
| kea-dhcp4.alloc-engine | core | database, i.e. |
| kea-dhcp6.alloc-engine | | create, modify |
| | | and remove DHCP |
| | | leases as a |
| | | result of |
| | | processing |
| | | messages from the |
| | | clients. |
|-----------------------------+----------------------+-------------------|
| | | Used by the DHCP |
| | | servers for |
| | | logging inbound |
| | | client packets |
| | | that were dropped |
| | | or to which the |
| | | server responded |
| kea-dhcp4.bad-packets | core | with a DHCPNAK. |
| kea-dhcp6.bad-packets | | It allows |
| | | administrators to |
| | | configure a |
| | | separate log |
| | | output that |
| | | contains only |
| | | packet drop and |
| | | reject entries. |
|-----------------------------+----------------------+-------------------|
| | | Used to log |
| | | messages |
| | | pertaining to the |
| kea-dhcp4.callouts | core | callouts |
| kea-dhcp6.callouts | | registration and |
| | | execution for the |
| | | particular hook |
| | | point. |
|-----------------------------+----------------------+-------------------|
| | | Used to log |
| | | messages relating |
| | | to the handling |
| kea-dhcp4.commands | core | of commands |
| kea-dhcp6.commands | | received by the |
| | | the DHCP server |
| | | over the command |
| | | channel. |
|-----------------------------+----------------------+-------------------|
| | | Used by the DHCP |
| | | server to log |
| | | messages related |
| | | to the Client |
| kea-dhcp4.ddns | | FQDN and Hostname |
| kea-dhcp6.ddns | core | option |
| | | processing. It |
| | | also includes log |
| | | messages related |
| | | to the relevant |
| | | DNS updates. |
|-----------------------------+----------------------+-------------------|
| | | Used by the |
| kea-dhcp4.dhcp4 | core | DHCPv4 server |
| | | daemon to log |
| | | basic operations. |
|-----------------------------+----------------------+-------------------|
| | | The base loggers |
| kea-dhcp4.dhcpsrv | core | for the |
| kea-dhcp6.dhcpsrv | | libkea-dhcpsrv |
| | | library. |
|-----------------------------+----------------------+-------------------|
| | | Used to log |
| | | messages relating |
| kea-dhcp4.eval | core | to the client |
| kea-dhcp6.eval | | classification |
| | | expression |
| | | evaluation code. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| kea-dhcp4.host-cache-hooks | libdhcp_host_cache | messages related |
| kea-dhcp6.host-cache-hooks | premium hook library | to operation of |
| | | the Host Cache |
| | | Hook Library. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| kea-dhcp4.flex-id-hooks | libdhcp_flex_id | messages related |
| kea-dhcp6.flex-id-hooks | premium hook library | to operation of |
| | | the Flexible |
| | | Identifiers Hook |
| | | Library. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| kea-dhcp4.ha-hooks | libdhcp_ha hook | messages related |
| kea-dhcp6.ha-hooks | library | to operation of |
| | | the High |
| | | Availability Hook |
| | | Library. |
|-----------------------------+----------------------+-------------------|
| | | Used to log |
| | | messages related |
| | | to management of |
| | | hooks libraries, |
| | | e.g. registration |
| | | and |
| kea-dhcp4.hooks | | deregistration of |
| kea-dhcp6.hooks | core | the libraries, |
| | | and to the |
| | | initialization of |
| | | the callouts |
| | | execution for |
| | | various hook |
| | | points within the |
| | | DHCP server. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| | | messages related |
| | | to operation of |
| | | the Host Cmds |
| | | hooks library. In |
| kea-dhcp4.host-cmds-hooks | libdhcp_host_cmds | general these |
| kea-dhcp6.host-cmds-hooks | premium hook library | will pertain to |
| | | loading and |
| | | unloading the |
| | | library and the |
| | | execution of |
| | | commands by the |
| | | library. |
|-----------------------------+----------------------+-------------------|
| | | Used within the |
| | | libdhcpsrv and it |
| | | logs messages |
| | | related to the |
| kea-dhcp4.hosts | | management of the |
| kea-dhcp6.hosts | core | DHCP host |
| | | reservations, |
| | | i.e. retrieval of |
| | | the reservations |
| | | and adding new |
| | | reservations. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| | | messages related |
| | | to operation of |
| | | the Lease Cmds |
| | | hooks library. In |
| kea-dhcp4.lease-cmds-hooks | libdhcp_lease_cmds | general these |
| kea-dhcp6.lease-cmds-hooks | hook library | will pertain to |
| | | loading and |
| | | unloading the |
| | | library and the |
| | | execution of |
| | | commands by the |
| | | library. |
|-----------------------------+----------------------+-------------------|
| | | Used by the DHCP |
| | | server to log |
| | | messages related |
| | | to the lease |
| | | allocation. The |
| kea-dhcp4.leases | | messages include |
| kea-dhcp6.leases | core | detailed |
| | | information about |
| | | the allocated or |
| | | offered leases, |
| | | errors during the |
| | | lease allocation |
| | | etc. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| kea-dhcp4.legal-log-hooks | libdhcp_legal_log | messages related |
| kea-dhcp6.legal-log-hooks | premium hook library | to operation of |
| | | the Forensic |
| | | Logging Hooks |
| | | Library. |
|-----------------------------+----------------------+-------------------|
| | | Used by the DHCP |
| | | server to log |
| | | messages related |
| | | to processing of |
| | | the options in |
| | | the DHCP |
| kea-dhcp4.options | | messages, i.e. |
| kea-dhcp4.options | core | parsing options, |
| | | encoding options |
| | | into on-wire |
| | | format and packet |
| | | classification |
| | | using options |
| | | contained in the |
| | | received packets. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | mostly used to |
| | | log messages |
| | | related to |
| | | transmission of |
| | | the DHCP packets, |
| | | i.e. packet |
| | | reception and |
| | | sending a |
| | | response. Such |
| | | messages include |
| | | information about |
| | | the source and |
| | | destination IP |
| | | addresses and |
| | | interfaces used |
| | | to transmit |
| kea-dhcp4.packets | core | packets. The |
| kea-dhcp6.packets | | logger is also |
| | | used to log |
| | | messages related |
| | | to subnet |
| | | selection, as |
| | | this selection is |
| | | usually based on |
| | | the IP addresses, |
| | | relay addresses |
| | | and/or interface |
| | | names, which can |
| | | be retrieved from |
| | | the received |
| | | packet, even |
| | | before the DHCP |
| | | message carried |
| | | in the packet is |
| | | parsed. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| kea-dhcp4.radius-hooks | libdhcp_radius | messages related |
| kea-dhcp6.radius-hooks | premium hook library | to operation of |
| | | the Radius Hook |
| | | Library. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| | | messages related |
| | | to operation of |
| | | the Stats Cmds |
| | | hooks library. In |
| kea-dhcp4.stat-cmds-hooks | libdhcp_stat_cmds | general these |
| kea-dhcp6.stat-cmds-hooks | hook library | will pertain to |
| | | loading and |
| | | unloading the |
| | | library and the |
| | | execution of |
| | | commands by the |
| | | library. |
|-----------------------------+----------------------+-------------------|
| | | This logger is |
| | | used to log |
| | | messages related |
| | | to operation of |
| | | the Subnet Cmds |
| | | hooks library. In |
| kea-dhcp4.subnet-cmds-hooks | libdhcp_subnet_cmds | general these |
| kea-dhcp6.subnet-cmds-hooks | hook library | will pertain to |
| | | loading and |
| | | unloading the |
| | | library and the |
| | | execution of |
| | | commands by the |
| | | library. |
|-----------------------------+----------------------+-------------------|
| | | The root logger |
| | | for the |
| | | kea-dhcp-ddns |
| | | daemon. All |
| | | components used |
| kea-dhcp-ddns | core | by this daemon |
| | | inherit the |
| | | settings from |
| | | this logger if |
| | | there is no |
| | | specialized |
| | | logger provided. |
|-----------------------------+----------------------+-------------------|
| | | The logger used |
| | | by the |
| | | kea-dhcp-ddns |
| | | daemon for |
| kea-dhcp-ddns.dctl | core | logging basic |
| | | information about |
| | | the process, |
| | | received signals |
| | | and triggered |
| | | reconfigurations. |
|-----------------------------+----------------------+-------------------|
| | | The logger used |
| | | by the |
| | | kea-dhcp-ddns |
| kea-dhcp-ddns.dhcpddns | core | daemon for |
| | | logging events |
| | | related to DDNS |
| | | operations. |
|-----------------------------+----------------------+-------------------|
| | | Used by the |
| | | kea-dhcp-ddns |
| | | daemon for |
| | | logging |
| | | information about |
| kea-dhcp-ddns.dhcp-to-d2 | core | events dealing |
| | | with receiving |
| | | messages from the |
| | | DHCP servers and |
| | | adding them to |
| | | the queue for |
| | | processing. |
|-----------------------------+----------------------+-------------------|
| | | Used by the |
| | | kea-dhcp-ddns |
| | | daemon for |
| | | logging |
| kea-dhcp-ddns.d2-to-dns | core | information about |
| | | events dealing |
| | | with sending and |
| | | receiving |
| | | messages with the |
| | | DNS servers. |
+------------------------------------------------------------------------+
Note that user-defined hook libraries should not use any of those loggers
but should define new loggers with names that correspond to the libraries
using them. Suppose that the user created the library called
"libdhcp-packet-capture" to dump packets received and transmitted by the
server to the file. The appropriate name for the logger could be
kea-dhcp4.packet-capture-hooks. (Note that the hook library implementor
only specifies the second part of this name, i.e. "packet-capture". The
first part is a root logger name and is prepended by the Kea logging
system.) It is also important to note that since this new logger is a
child of a root logger, it inherits the configuration from the root
logger, something that can be overridden by an entry in the configuration
file.
Additional loggers may be defined in future versions of Kea. The easiest
way to find out the logger name is to configure all logging to go to a
single destination and look for specific logger names. See Section 18.1.2,
"Logging Message Format" for details.
18.1.1.2. severity (string)
This specifies the category of messages logged. Each message is logged
with an associated severity which may be one of the following (in
descending order of severity):
* FATAL - associated with messages generated by a condition that is so
serious that the server cannot continue executing.
* ERROR- associated with messages generated by an error condition. The
server will continue executing, but the results may not be as
expected.
* WARN - indicates an out of the ordinary condition. However, the server
will continue executing normally.
* INFO - an informational message marking some event.
* DEBUG - messages produced for debugging purposes.
When the severity of a logger is set to one of these values, it will only
log messages of that severity and above (e.g. setting the logging severity
to INFO will log INFO, WARN, ERROR and FATAL messages). The severity may
also be set to NONE, in which case all messages from that logger are
inhibited.
Note
The keactrl tool, described in Chapter 6, Managing Kea with keactrl, can
be configured to start the servers in the verbose mode. If this is the
case, the settings of the logging severity in the configuration file will
have no effect, i.e. the servers will use logging severity of DEBUG
regardless of the logging settings specified in the configuration file. If
you need to control severity via configuration file, please make sure that
the kea_verbose value is set to "no" within the keactrl configuration.
18.1.1.3. debuglevel (integer)
When a logger's severity is set to DEBUG, this value specifies what level
of debug messages should be printed. It ranges from 0 (least verbose) to
99 (most verbose). If severity for the logger is not DEBUG, this value is
ignored.
18.1.1.4. output_options (list)
Each logger can have zero or more output_options. These specify where log
messages are sent. These are explained in detail below.
18.1.1.4.1. output (string)
This value determines the type of output. There are several special values
allowed here: stdout (messages are printed on standard output), stderr
(messages are printed on stderr), syslog (messages are logged to syslog
using default name, syslog:name (messages are logged to syslog using
specified name). Any other value is interpreted as a filename to which
messages should be written.
18.1.1.4.2. flush (true of false)
Flush buffers after each log message. Doing this will reduce performance
but will ensure that if the program terminates abnormally, all messages up
to the point of termination are output. The default is "true".
18.1.1.4.3. maxsize (integer)
Only relevant when the destination is a file. This is maximum size in
bytes that a log file may reach. When the maximum size is reached, the
file is renamed and a new file opened. For example, a ".1" is appended to
the name -- if a ".1" file exists, it is renamed ".2", etc. This is
referred to as rotation.
The default value is 10240000 (10MB). The smallest value that may be
specified without disabling rotation is 204800. Any value less than this,
including 0, disables rotation.
Note
Due to a limitation of the underlying logging library (log4cplus), rolling
over the log files (from ".1" to ".2", etc) may show odd results: There
can be multiple small files at the timing of roll over. This can happen
when multiple processes try to roll over the files simultaneously. Version
1.1.0 of log4cplus solved this problem, so if this version or later of
log4cplus is used to build Kea, it should not happen. Even for older
versions it is normally expected to happen rarely unless the log messages
are produced very frequently by multiple different processes.
18.1.1.4.4. maxver (integer)
Only relevant when the destination is file and rotation is enabled (i.e.
maxsize is large enough). This is maximum number of rotated versions that
will be kept. Once that number of files has been reached, the oldest file,
"log-name.maxver", will be discarded each time the log rotates. In other
words, at most there will be the active log file plus maxver rotated
files. The minimum and default value is 1.
18.1.1.5. Example Logger Configurations
In this example we want to set the global logging to write to the console
using standard output.
"Logging": {
"loggers": [
{
"name": "kea-dhcp4",
"output_options": [
{
"output": "stdout"
}
],
"severity": "WARN"
}
]
}
In this second example, we want to store debug log messages in a file that
is at most 2MB and keep up to 8 copies of old logfiles. Once the logfile
grows to 2MB, it will be renamed and a new file file be created.
"Logging": {
"loggers": [
{
"name": "kea-dhcp6",
"output_options": [
{
"output": "/var/log/kea-debug.log",
"maxver": 8,
"maxsize": 204800,
"flush": true
}
],
"severity": "DEBUG",
"debuglevel": 99
}
]
}
18.1.2. Logging Message Format
Each message written to the configured logging destinations comprises a
number of components that identify the origin of the message and, if the
message indicates a problem, information about the problem that may be
useful in fixing it.
Consider the message below logged to a file:
2014-04-11 12:58:01.005 INFO [kea-dhcp4.dhcpsrv/27456]
DHCPSRV_MEMFILE_DB opening memory file lease database: type=memfile universe=4
Note: the layout of messages written to the system logging file (syslog)
may be slightly different. This message has been split across two lines
here for display reasons; in the logging file, it will appear on one line.
The log message comprises a number of components:
2014-04-11 12:58:01.005
The date and time at which the message was generated.
INFO
The severity of the message.
[kea-dhcp4.dhcpsrv/27456]
The source of the message. This comprises two elements: the Kea
process generating the message (in this case, kea-dhcp4) and the
component within the program from which the message originated
(dhcpsrv, which is the name of the common library used by DHCP
server implementations). The number after the slash is a process
id (pid).
DHCPSRV_MEMFILE_DB
The message identification. Every message in Kea has a unique
identification, which can be used as an index into the Kea
Messages Manual (http://kea.isc.org/docs/kea-messages.html) from
which more information can be obtained.
opening memory file lease database: type=memfile universe=4
A brief description. Within this text, information relating to the
condition that caused the message to be logged will be included.
In this example, the information is logged that the in-memory
lease database backend will be used to store DHCP leases.
18.1.3. Logging During Kea Startup
The logging configuration is specified in the configuration file. However,
when Kea starts, the file is not read until some way into the
initialization process. Prior to that, the logging settings are set to
default values, although it is possible to modify some aspects of the
settings by means of environment variables. Note that in the absence of
any logging configuration in the configuration file, the settings of
(possibly modified) default configuration will persist while the program
is running.
The following environment variables can be used to control the behavior of
logging during startup:
KEA_LOCKFILE_DIR
Specifies a directory where the logging system should create its
lock file. If not specified, it is prefix/var/run/kea, where
prefix defaults to /usr/local. This variable must not end with a
slash. There is one special value: "none", which instructs Kea to
not create lock file at all. This may cause issues if several
processes log to the same file.
KEA_LOGGER_DESTINATION
Specifies logging output. There are several special values.
stdout
Log to standard output.
stderr
Log to standard error.
syslog[:fac]
Log via syslog. The optional fac (which is separated
from the word "syslog" by a colon) specifies the
facility to be used for the log messages. Unless
specified, messages will be logged using the facility
"local0".
Any other value is treated as a name of the output file. If not
specified otherwise, Kea will log to standard output.
Chapter 19. The Kea Shell
Table of Contents
19.1. Overview
19.2. Shell Usage
19.1. Overview
Kea 1.2.0 introduced the Control Agent (CA, see Chapter 7, Kea Control
Agent) that provides a RESTful control interface over HTTP. That API is
typically expected to be used by various IPAMs and similar management
systems. Nevertheless, there may be cases when you want to send a command
to the CA directly. The Kea Shell provides a way to do this. It is a
simple command-line, scripting-friendly text client that is able connect
to the CA, send it commands with parameters, retrieve the responses and
display them.
As the primary purpose of the Kea Shell is as a tool in scripting
environment, it is not interactive. However, with simple tricks it can be
run manually.
19.2. Shell Usage
kea-shell is run as follows:
kea-shell [--host hostname] [--port number] [--path path] [--timeout seconds] [--service service-name] [command]
where:
* --host hostname specifies the hostname of the CA. If not specified,
"localhost" is used.
* --port number specifies the TCP port on which the CA listens. If not
specified, 8000 is used.
* --path path specifies the path in the URL to connect to. If not
specified, empty path is used. As CA listens at the empty path this
parameter is useful only with a reverse proxy.
* --timeout seconds specifies the timeout (in seconds) for the
connection. If not given, 10 seconds is used.
* --service service-name specifies the target of a command. If not
given, CA will be used as target. May be used more than once to
specify multiple targets.
* command specifies the command to be sent. If not specified,
list-commands command is used.
Other switches are:
* -h prints a help message.
* -v prints the software version.
Once started, the shell reads parameters for the command from standard
input, which are expected to be in JSON format. When all have been read,
the shell establishes a connection with the CA using HTTP, sends the
command and awaits a response. Once that is received, it is printed on
standard output.
For a list of available commands, see Chapter 16, Management API.
Additional commands may be provided by hook libraries. If unsure which
commands are supported, use the list-commands command. It will instruct
the CA to return a list of all supported commands.
The following shows a simple example of usage:
$ kea-shell --host 192.0.2.1 --port 8001 --service dhcp4 list-commands
^D
After the command line is entered, the program waits for command
parameters to be entered. Since list-commands does not take any arguments,
CTRL-D (represented in the above example by "^D") is pressed to indicate
end of file (and so terminate the parameter input). The Shell will then
contact the CA and print out the list of available commands returned for
the service named dhcp4.
It is envisaged that Kea Shell will be most frequently used in scripts.
The next example shows a simple scripted execution. It sends the command
"config-write" to the CA ( --service parameter hasn't been used), along
with the parameters specified in param.json. The result will be stored in
result.json.
$ cat param.json
"filename": "my-config-file.json"
$ cat param.json | kea-shell --host 192.0.2.1 config-write > result.json
When a reverse proxy is used to de-multiplex requests to different servers
the default empty path in the URL is not enough so the --path parameter
should be used. For instance if requests to the "/kea" path are forwarded
to the CA this can be used:
$ kea-shell --host 192.0.2.1 --port 8001 --path kea ...
Kea Shell requires Python to to be installed on the system. It was tested
with Python 2.7 and various versions of Python 3, up to 3.5. Since not
every Kea deployment uses this feature and there are deployments that do
not have Python, the Kea Shell is not enabled by default. To use it, you
must specify --enable-shell to when running "configure" during the
installation of Kea.
The Kea Shell is intended to serve more as a demonstration of the RESTful
interface capabilities (and, perhaps, an illustration for people
interested in integrating their management evironments with Kea) than as a
serious management client. Do not expect it to be significantly expanded
in the future. It is, and will remain, a simple tool.
Chapter 20. Frequently Asked Questions
Table of Contents
20.1. General Frequently Asked Questions
20.1.1. Where did the Kea name came from?
20.1.2. Feature X is not supported yet. When/if will it be
available?
20.2. Frequently Asked Questions about DHCPv4
20.2.1. I set up a firewall, but the Kea server still
receives the traffic. Why?
20.3. Frequently Asked Questions about DHCPv6
20.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I
checked with tcpdump (or other traffic capture software) that
the incoming traffic is reaching the box. What's wrong?
This chapter contains a number of frequently asked questions and
troubleshooting tips. It currently lacks content, but it is expected to
grow over time.
20.1. General Frequently Asked Questions
20.1.1. Where did the Kea name came from?
Kea is the name of a high mountain parrot living in New Zealand. See this
https://lists.isc.org/pipermail/kea-users/2014-October/000032.html for an
extended answer.
20.1.2. Feature X is not supported yet. When/if will it be available?
Kea is developed by a small team of engineers. Our resources are limited,
so we need to prioritize requests. The complexity of a new feature (how
difficult it is to implement a feature and how likely it would break
something that already works), amount of work required and expected
popularity (i.e., how many users would actually benefit from it) are three
leading factors. We sometimes also have contractual obligations.
Simply stating that you'd like feature X is useful. We try to implement
features that are actively requested first, but the reality is that we
have more requests than we can handle, so some of them must be postponed,
at least in the near future. So is your request likely to be rejected? Not
at all. You can do many things to greatly improve the chances of your
request being fulfilled. First, it helps to explain why you need a
feature. If your explanation is reasonable and there are likely other
users that would benefit from it, the chances for Kea developers to put
this task on a roadmap is better. Saying that you are willing to
participate in tests (e.g., test engineering drops when they become
available) is also helpful.
Another thing you can do to greatly improve the chances of a feature to
appear is to actually develop it on your own and submit a patch. That's an
avenue that people often forget about. Kea is open source software and we
do accept patches. There are certain requirements, like code quality,
comments, unit-tests, documentation, etc., but we have accepted a
significant number of patches in the past, so it's doable. Accepted
contributions range from minor documentation corrections to significant
new features, like support for a new database type. Before considering
writing and submitting a patch, make sure you read the Contributor's Guide
in the Kea Developer's Guide.
Kea is developed by ISC, which is a non-profit organization. You may
consider signing a development contract with us. In the past we did
implement certain features due to contractual obligations. With additional
funds we are able to put extra engineering efforts into Kea development.
We can reshuffle our schedule or add extra hands to the team if needed.
Please keep in mind that Kea is open source software and its principle
goal is to provide a good DHCP solution that can be used by everyone. In
other words, we may refuse a contract that would tie the solution to
specific proprietary technology or make it unusable for other users. Also,
we strive to make Kea a reference implementation, so if your proposal
significantly violates a RFC, we may have a problem with that.
Nevertheless, please talk to us and we may be able to find a solution.
Finally, Kea has a public roadmap, with releases happening several times
each year. We tend to not modify plans for the current milestone, unless
there are very good reasons to do so. Therefore "I'd like a feature X in 6
months" is much better received than "I'd like a feature X now".
20.2. Frequently Asked Questions about DHCPv4
20.2.1. I set up a firewall, but the Kea server still receives the traffic.
Why?
Any DHCPv4 server must be able to receive from and send traffic to hosts
that don't have an IPv4 address assigned yet. That is typically not
possible with regular UDP sockets, therefore the Kea DHCPv4 server uses
raw sockets by default. Raw sockets mean that the incoming packets are
received as raw Ethernet frames, thus bypassing the whole kernel IP stack,
including any firewalling rules your kernel may provide.
If you do not want the server to use raw sockets, it is possible to
configure the Kea DHCPv4 server to use UDP sockets instead. See
dhcp-socket-type described in Section 8.2.4, "Interface Configuration".
However, using UDP sockets has certain limitations. In particular, they
may not allow for sending responses directly to clients without IPv4
addresses assigned. That's ok, if all your traffic is coming through relay
agents.
20.3. Frequently Asked Questions about DHCPv6
20.3.1. Kea DHCPv6 doesn't seem to get incoming traffic. I checked with
tcpdump (or other traffic capture software) that the incoming traffic is
reaching the box. What's wrong?
Please check whether your OS has any IPv6 filtering rules. Many operating
systems are shipped with firewalls that discard incoming IPv6 traffic by
default. In particular, many Linux distributions do that. Please check the
output of the following command:
# ip6tables -L -n
One common mistake in this area is to use iptables tool, which lists IPv4
firewall rules only.
Chapter 21. Acknowledgments
Kea is an open source project designed, developed, and maintained by
Internet Systems Consortium, Inc, a 501(c)3 non-profit organization. ISC
is primarily funded by revenues from support subscriptions for our open
source and we encourage all professional users to consider this option. To
learn more, see *https://www.isc.org/support/.
If you would like to contribute to ISC to assist us in continuing to make
quality open source software, please visit our donations page at
*http://www.isc.org/donate/.
We thank all the organizations and individuals who have helped to make Kea
possible. Comcast and the Comcast Innovation Fund provided major support
for the development of Kea's DHCPv4, DHCPv6 and DDNS modules. Mozilla
funded initial work on the REST API via a MOSS award.
Kea was initially implemented as a collection of applications within the
BIND 10 framework. We thank the founding sponsors of the BIND10 project:
Afilias, IIS.SE, Nominet, SIDN, JPRS, CIRA; and additional sponsors AFNIC,
CNNIC, CZ.NIC, DENIC eG, Google, RIPE NCC, Registro.br, .nz Registry
Services, and Technical Center of Internet .