ZXR105900ESeriesCongurationGuide(IPv4Routing)
byaroutercarriesallLSPabstractinformationthatisavailableintherouterlinkstate
database.ButthePSNPonlycarriesasubsetoftheinformation.
TheSRMandtheSSNaremainlyusedforrouterselectioninformationdiffusionand
databasesynchronization.
lPoint-to-pointlinks
TheIS-ISprotocolusesareliableoodingmechanismonpoint-to-pointlinks.Ona
point-to-pointlink,thereisonlyoneneighborrouterontheoppositeendofthelink,
andtherouteruseslimitedbandwidthtotraceacknowledgemessagessentbythe
neighborrouter.
TheCSNPsimpliesthedatabasesynchronizationprocess.Whentheneighbor
relationbetweentwoconnectedroutersisestablishedforthersttime,allCSNPson
thepoint-to-pointlinkareexchanged.ThroughcomparingtheCSNPwiththelocal
databaseandthedatabaseofeachneighborrouter,themissingorexpiredLSPcan
beconrmed.
UsethePSNPtoapplyforthemissingortheLSPofthecurrentversion.Iftherouter
ndsthatsomeneighborrouterslacktheLSP ,theroutercanoodtheLSP .Duringthe
ooding,usetheSSNtoidentifythatitisthePSNPthatneedstobesent,andusethe
SRMtoidentifythatitistheLSPthatneedstobesent.WhenthePSNPacknowledge
packetisreceivedfromthepeerend,theSRMtagcanbecleared.Iftheacknowledge
packetisnotreceived,thecorrespondingpacketisresentaftertimeout.
Fortheexampleofthediffusionprocessonpoint-to-pointnetworks,seeFigure4-6.
TheneighborrelationbetweenRTBandRTCisnormal,andRTAandRTBestablish
theadjacentrelationforthersttime.
Figure4-6Point-to-pointDiffusionandDatabaseSynchronization
1.Theprocessforestablishingtheadjacentrelationanddatabasesynchronization
isasfollows:
StepRTARTB
1SendCSNPsendCSNP
2-ReceivestheCSNPfromRTAand
sendsthePSNPrequest.TheRTA's
CSNPislost.RTBndstheLSPof
thelocallinkstatedatabasethatis
lostbytheRTA'CSNP ,RTBsendsthe
RTC.00-00LSPtoRTA.
3ReceivesthePSNPandsendsRTA.00-00
LSP
-
4-8
SJ-20150114102049-003|2015-01-15(R1.0)ZTEProprietaryandCondential