Zte ZXR10 5900E Series - Configuring BGP

ZXR105900ESeriesCongurationGuide(IPv4Routing)
3.Activestate:TheBGPalwaystriestoestablishTCPconnection.Iftheconnection
timertimesout,thentheBGPreturnstoConnectstate.IfTCPconnectionis
successful,thenBGPentersOpenSentstate.
4.OpenSentstate
TCPconnectionisestablishedalready.TheBGPsendstherstOPENpacket
andwaitsforthereplyfromthepeer.BGPexaminesthereplypacket.IftheBGP
ndserror,itwillsendaNOTIFICATIONpacketandreturntoIdlestate.Ifthere
isnoerrorinthereplypacket,BGPwillsendaKEEPALIVEpacket.KEEKALIVE
timerstartstiming.TheBGPentersintoOpenConrmstate.
5.OpenConrmstate
TheBGPwaitsforKEEPALIVEpacketandresetstheKEEPALIVEtimer.When
theBGPreceivesaKEEPALIVEpacket,itentersEstablishedstate.
6.Establishedstate
Neighborhoodissetupalready.RouterexchangesUpdatepacketwithits
neighbor,andmeanwhile,theKEEPALIVEtimerisreset.
Ininitial,theexchangingofroutinginformationincludesallBGProutes,thatis,all
entriesinBGProutingtablewillbeexchanged.Aftertheinitialexchangingisnished,
theincrementalandburstroutingupdateislaunchedonlywhentherouteentriesare
changedorbeenunavailable.Themeaningoftheso-calledincrementalisthatnotthe
entityBGPtablewillbeexchangedbutonlyupdatethechangedrouteentries.The
burstmeansthatupdateroutesonlywhentheroutingtableischangedratherthan
periodicallyrouteupdating.
Whenaroutersendsrouteinformationtoitsneighbor,itwillsavetherouteentriessent
toneighboratlocal.Whentherouterreceivesarouteupdatingpacket,itwillcompare
updatingpacketwiththelocallysavedroutingentries.Ifthisentryisnotsentbefore,
thentherouterwillsendittoitsneighbor.Iftheentryissentalreadyandbetter,the
routerwillsendtheentrytoitsneighborandupdateitslocallysavedroutingentries.
Comparedwiththeconventionalperiodicalroutingtableupdating,thisupdatingmode
savesthebandwidthalot.RouteupdatingisachievedbyUPDATEpackets.
Duringtheprocessabove,iftheBGPconnectionfailstobeestablishedbecauseof
anyconnectionfailure,authenticationfailureandrouteloopbackandsoon,therouter
willsendNOTIFICATIONpackettoitspeerthatcloseBGPsessionwillbeclosed.
Later,therouterentersIdlestate.
5.2ConguringBGP
BGPNeighborhoodEstablishment
TworoutersarecalledaspeersorneighborsifBGPsessionissetupbetweenthem.
Therearetwoconnectionmodesofpeers,IBGPandEBGP.Ifthetworouterswhich
exchangeBGPpacketsbelongtothesameAS,thenthesetworoutersadoptIBGPas
5-4
SJ-20150114102049-003|2015-01-15(R1.0)ZTEProprietaryandCondential