Ellhniko Bridging mini-Howto
Christopher Cole cole@coledd.com
v1.11, 7 Septembrioy 1998
To eggrafo ayto perigrafei pws na sthsete mia ethernet gefyra. Ti
einai mia ethernet gefyra; Einai mia syskeyh poy elegxei ta paketa
dedomenwn mesa se ena ypodiktyo prospa8wntas na meiwsei thn kyklofo
ria. H gefyra einai synh8ws metaju duo jexwristwn omadwn ypologistwn,
poy enw miloun polu metaju toys, spaniws mila h mia omada me thn allh.
Ena kalo paradeigma einai an skeftoume mia omada me Macintosh kai mia
omada me Unix mhxanhmata. Kai oi duo omades exoyn ayjhmenh kinhsh
entos toys, opote h kinhsh ayth dhmioyrgei sygkrouseis me thn kinhsh
ths allhs omadas. H gefyra topo8eteite metaju twn duo omadwn. H
doyleia ths einai na elegxei ta dedomena poy antallassontai kai na
apofasisei an xreiazetai na perasoyn sthn allh pleyra ths gefyras. To
apotelesma einai ena grhgorotero kai pio isxyro diktyo me ligoteres
sygkrouseis. --- Gia opoiadhpote sxolia, dior8wseis, klp sxetika me
thn ellhnikh metafrash epikoinwnhste me ton Panagiwth Boydourh sth
dieu8ynsh: panos@veria1.freeserve.co.uk
______________________________________________________________________
Table of Contents
1. Setup
2. Syxna problhmata
______________________________________________________________________
1. Setup
1. Breite to ``Bridge Config'':
<ftp://shadow.cabi.net/pub/Linux/BRCFG.tgz>
2. Energopoihste pollaples ethernet syskeyes bazontas to parakatw sto
/etc/lilo.conf, kai jana-trexontas to lilo:
append = "ether=0,0,eth1"
An exete treis syskeyes sth gefyra balte to parakatw anti twn anw:
append = "ether=0,0,eth1 ether=0,0,eth2"
Perissoteres syskeyes mporoun na proste8oun me perissoteres dhlwseis
ether. Enas etoimos pyrhnas caxnei gia mia karta kai molis th brei
stamata to cajimo. Me thn parapanw entolh synexizei na caxnei kai meta
thn prwth karta.
Anti twn anw, mporeite na xrhsimopoihsete thn parakatw parametro
ekkinhshs:
linux ether=0,0,eth1
H me 3 syskeyes:
linux ether=0,0,eth1 ether=0,0,eth2
3. Anametalwttiste ton pyrhna me to BRIDGING energopoihmeno.
4. H gefyra de 8a prepei na exei IP dieu8ynsh. MPOREI na exei alla mia
aplh gefyra den thn xreiazetai. Gia na afairesete thn IP dieu8ynsh
apo th gefyra sas, phgainete sto /etc/sysconfig/network-
scripts/ (gia RedHat susthma) kai antigracte to ifcfg-lo0 se ifcfg-
eth0 & ifcfg-eth1. Sta duo ayta arxeia allajte th grammh poy
periexei to ``DEVICE=lo'' se ``DEVICE=eth0'' kai ``DEVICE=eth1''.
Alles dianomes mporei na diaferoyn, kante o,ti xreiazetai! An exete
panw apo duo syskeyes sth gefyra sigoyreyteite na dior8wsete oles
tis ry8miseis.
5. Epanekkinhsh, wste na exete ton neo pyrhna kai janasigoyreyteite
oti h gefyra den exei IP diey8unseis.
6. Molis to susthma jekinhsei, balte tis ethernet kartes se
promiscuous mode, wste na elegxoyn otidhpote pernaei apo aytes:
ifconfig eth0 promisc ; ifconfig eth1 promisc
Oles oi kartes poy einai na synde8oun se gefyra prepei na mpoyn se
promiscuous mode.
7. Energopoihste to bridging xrhsimopoiwntas to programma brcfg:
brcfg -ena
8. Bebaiw8eite oti yparxei diaforetikh kinhsh se ka8e tmhma:
tcpdump -i eth0 (in one window)
tcpdump -i eth1 (in another window)
9. Trejte ena sniffer h to tcpdump se allo mhxanhma gia na deite oti h
gefyra apokoptei ta tmhmata kanonika.
2. Syxna problhmata
1.
Question
Pairnw to mhnyma
ioctl(SIOCGIFBR) failed: Package not installed
Ti shmainei;
Answer
Den exete bridging dynatothtes ston pyrhna. Parte pyrhna 2.0 h
megalutero, kai anametaglwttiste to me thn epilogh BRIDGING
energopoihmenh.
2.
Question
Mhxanhmata sth mia pleyra de mporoun na kanoyn ping sthn allh!
Answer
· Energopoihsate to bridging me ``brcfg -ena''; (to brcfg 8a
prepei na leei ``bridging is ENABLED'')
· Balate tis kartes se promiscuous mode? (gracte ``ifconfig''.
To ``PROMISC'' prepei na emfanistei kai stis duo pleyres.)
· An xrhsimopoieite kartes diasundeshs pollaplwn meswn
sigoyreyteite oti to swsto exei energopoih8ei. Isws xreiastei na
xrhsimopoihsete to programma ry8misewn poy phrate me thn karta.
3.
Question
De mporw na kanw telnet/ftp apo th gefyra! Giati;
Answer
Ayto de ginetai efoson den yparxei IP dieu8ynsh sth gefyra. H
gefyra prepei na einai ena diafano meros toy diktuoy.
4.
Question
Ti prepei na kanw gia na ry8misw th dromologhsh;
Answer
Tipota! H dromologhsh elegxetai apo ton kwdika toy pyrhna. Gia
na deite tis ethernet diey8unseis opws ma8ainontai apo th gefyra
xrhsimopoihste to brcfg se debug mode:
brcfg -deb
5.
Question
H gefyra fainetai na doyleuei, alla to ``traceroute'' de deixnei
th gefyra ws meros ths diadromhs.
Answer
Logw ths fushs ths gefyras, to ``traceroute'' DEN prepei na
deijei th gefyra. H gefyra einai diafanhs sto diktyo.
6.
Question
Einai aparaithto na metaglwttisw ton pyrhna me IP_FORWARD;
Answer
Oxi. O kwdikas gia to bridging ston pyrhna frontizei gia th
metafora. To IP_FORWARD einai gia pulh poy exei IP dieu8ynsh.
7.
Question
Giati oi diey8unseis gia th 8ura 1 kai 8ura 2 einai idies
sumfwna me to ``brcfg''; De 8a eprepe na einai diaforetikes;
Answer
Oxi. Ka8e 8ura sth gefyra exei epithdes thn idia dieu8ynsh, opws
dinetai apo ton kwdika toy bridging.
8.
Question
To bridging den emfanizetai ws epilogh otan kanw make config gia
ton pyrhna. Pws to energopoiw;
Answer
Kata thn parametropoihsh, apanthste 'Y' sthn erwthsh: ``Prompt
for development and/or incomplete code/drivers
(CONFIG_EXPERIMENTAL) [Y/n/?]''.
9.
Question
Polloi komboi (hubs, 4 h parapanw) syndemena se seira prokaloun
problhmata sygxronismou se ethernet. Ti epiptwseis exei ayto se
ena ypodiktyo poy einai sthmeno me hubs;
Answer
H gefyra anaorizei ton kanona twn 3/4/5 kombwn. H gefyra den
xeirizetai ta paketa dedomenwn opws ena hub, opote den
dhmioyrgei problhmata sygxronismou sto diktyo.
10.
Question
Mporei mia gefyra na syndesei duo tmhmata me 10Mb kai 100Mb;
Tetoia diamorfwsh 8a ephreasei thn taxuthta sthn grhgora pleyra;
Answer
Nai, h gefyra mporei na syndesei ena tmhma 10Mb me ena tmhma
100Mb. Efoson h karta diktuoy sto grhgoro diktyo ftanei ta
100Mb, to TCP frontizei gia ta ypoloipa. Fysika, ta dedomena apo
to grhgoro pros to argo tmhma 8a metaferontai me 10Mb/s, alla h
ypoloiph kinhsh sto grhgoro diktyo den epibradunetai.