Zte ZXR10 8900 Series User manual

ZXR108900Series
10GigabitRoutingSwitch
UserManual(MPLSVolume)
Version2.8.02.C
ZTECORPORATION
NO.55,Hi-techRoadSouth,ShenZhen,P .R.China
Postcode:518057
Tel:[phone]
Fax:[phone]
URL:http://ensupport.zte.com.cn
E-mail:[email protected]

LEGALINFORMATION
Copyright©2010ZTECORPORATION.
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TheultimaterighttointerpretthisproductresidesinZTECORPORATION.
RevisionHistory
RevisionNo.RevisionDateRevisionReason
R1.320100205Editionupdate
SerialNumber:sjzl20093840

Contents
AboutThisManual.............................................I
SafetyInstruction.............................................1
SafetyInstruction...........................................................1
SafetySigns..................................................................1
MPLSConguration...........................................3
MPLSOverview..............................................................3
MPLSFunction...........................................................3
IPForwardingFeatures................................................4
ATMForwardingFeatures.............................................4
MPLSFeatures...........................................................5
MPLSWorkingPrinciple...............................................6
MPLSTerms...................................................................7
MPLSLabel................................................................7
ForwardEquivalenceClass...........................................8
MPLSNetworkStructure..............................................9
LSPEstablishment..........................................................9
LSPEstablishmentProcedure......................................10
PenultimateHopPopping............................................12
LabelControlandManagement.......................................13
LabelDistributionMode..............................................14
LabelControlMode....................................................15
LabelHoldingMode....................................................15
LabelForwardingT able...............................................16
LabelDistributionProtocol..........................................16
LDPSessionEstablishmentandMaintenance.................17
ConguringMPLS..........................................................18
EnablingMPLS..........................................................18
ConguringLDPRouter-ID..........................................18
ConguringLabelDistributionandControl....................19
ConguringLDPTimeParameters................................20
ConguringMD5Password..........................................20
CondentialandProprietaryInformationofZTECORPORATIONI

ZXR108900SeriesUserManual(MPLSVolume)
ClearingLSRPeerConnection......................................20
MPLSCongurationExamples.........................................21
MPLSBasicCongurationExample...............................21
LabelDistributionExampleforSpeciedNerwork
Segment..........................................................23
MPLSMaintenanceandDiagnosis.....................................25
MPLSL3VPNConguration..............................29
MPLSL3VPNOverview....................................................29
RelatedTerms...........................................................30
VPN-IPv4AddressandRouteDistinguisher....................31
MPLSL3VPNWorkingPrinciples...................................32
MPLSL3VPNLoadBalance..........................................33
MPLSL3VPNLoadBalanceonSmartgroupLink..............34
ConguringMPLSL3VPN................................................35
ConguringOSPFinMPLSDomain...............................35
ConguringVRFonPE................................................36
ConguringStaticRoutebetweenCEandPE.................38
ConguringRIPbetweenCEandPE.............................39
ConguringOSPFbetweenCEandPE...........................40
ConguringEBGPbetweenCEandPE...........................42
ConguringMPBGP....................................................43
ConguringMPLSL3VPNLoadBalance.............................45
MPLSL3VPNCongurationExample.................................45
CongurationExampleofMPLSL3VPNLoadBalanceon
SmartgroupLink....................................................49
MPLSL2VPNConguration..............................51
MPLSL2VPNOverview....................................................51
VirtualPrivateWireService.........................................51
VirtualPrivateLANService.........................................52
ConguringMPLSL2VPN................................................54
ConguringVPWS......................................................54
ConguringVPLS.......................................................54
ConguringLayer2ControlMessageTransparent
TransmissionVPLSNetworkPolicy........................56
MPLSL2VPNCongurationExamples................................57
VPWSCongurationExample......................................57
VPLSCongurationExample.......................................58
Layer2ControlMessageTransparentTransmission
VPLSNetworkCongurationExample...................62
MPLSL2VPNMaintenanceandDiagnosis...........................62
IICondentialandProprietaryInformationofZTECORPORATION

VPWSMaintenanceandDiagnosis................................62
VPLSMaintenanceandDiagnosis.................................63
Layer2ControlMessageTransparentTransmission
VPLSNetworkCongurationMaintenanceand
Diagnosis.........................................................63
MPLSOAMConguration.................................65
FunctionIntroduction.....................................................65
CongureMPLSOAM......................................................66
MPLSTEHOT-STANDBYConguration.............69
MPLSTEHOT-STANDBYOverview....................................69
BasicCongurationofMPLSTEHOT-STANGBY..................69
MaintenanceandDiagnosisofMPLSTEHOT-STANDBY.........70
CongurationExampleofMPLSTEHOT-STANDBY..............70
Figures............................................................73
Glossary..........................................................75
CondentialandProprietaryInformationofZTECORPORATIONIII

ZXR108900SeriesUserManual(MPLSVolume)
Thispageisintentionallyblank.
IVCondentialandProprietaryInformationofZTECORPORATION

AboutThisManual
PurposeThismanualisZXR108900Series(V2.8.02.C)10GigabitRout-
ingSwitchUserManual(MPLSVolume)andappliestoZXR10
8902/8905/8908/891210Gigabitroutingswitch.
Intended
AudienceThismanualisintendedforthefollowingengineers:
�On-sitemaintenanceengineers
�Networkmonitoringengineers
�Systemmaintenanceengineers
WhatIsinThis
ManualThismanualcontainsthefollowingcontents:
ChapterOverview
Chapter1Safety
Instruction
Describessafetyinstructionsandsignsused
inthismanual.
Chapter2MPLS
Conguration
Thischapterdescribesbasicconcept,
congurationandcongurationexampleof
MPLS.
Chapter3MPLSL3VPN
Conguration
Thischapterdescribesbasicconcept,
congurationandcongurationexampleof
MPLSL3VPN.
Chapter4MPLSL2VPN
Conguration
Thischapterdescribesbasicconcept,
congurationandcongurationexampleof
MPLSL2VPN.
Chapter5MPLSOAM
Conguration
Thischapterdescribesbasicconcept,
congurationandcongurationexampleof
MPLSOAM.
Chapter6MPLS
TEHOT-STANDBY
Conguration
Thischapterdescribesbasicconcept,
congurationandcongurationexampleof
MPLSTEHOT-STANDBY .
Related
DocumentationThefollowingdocumentationisrelatedtothismanual:
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
HardwareInstallationManual
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
HardwareManual
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(BasicConguration)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(EthernetSwitching)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(IPv4Routing)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(IPv6)
CondentialandProprietaryInformationofZTECORPORATIONI

ZXR108900SeriesUserManual(MPLSVolume)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(MPLS)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(DPI)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitchUser
Manual(Firewall)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(Index)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(BasicCongurationVolumeI)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(BasicCongurationVolumeII)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(BasicCongurationVolumeIII)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(EthernetSwitching)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(IPv4RoutingVolumeI)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(IPv4RoutingVolumeII)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(IPv6)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(MPLS)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(NetworkManagement)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(QoS)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(Security)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(VoiceandVideo)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(Multicast)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(DPI)
�ZXR108900Series(V2.8.02.C)10GigabitRoutingSwitch
CommandReference(Firewall)
IICondentialandProprietaryInformationofZTECORPORATION

Chapter1
SafetyInstruction
TableofContents
SafetyInstruction...............................................................1
SafetySigns......................................................................1
SafetyInstruction
Onlydulytrainedandqualiedpersonnelcaninstall,operateand
maintainthedevices.
Duringthedeviceinstallation,operationandmaintenance,please
abidebythelocalsafetyspecicationsandrelatedoperationin-
structions,otherwisephysicalinjurymayoccurordevicesmaybe
broken.Thesafetyprecautionsmentionedinthismanualareonly
supplementoflocalsafetyspecications.
Thedebugcommandsonthedeviceswillaffecttheperformance
ofthedevices,whichmaybringseriousconsequences.Sotake
caretousedebugcommands.Especially,thedebugallcom-
mandwillopenalldebugprocesses,sothiscommandmustnot
beusedonthedeviceswithservices.Itisnotrecommendedto
usethedebugcommandswhentheusernetworksareinnormal
state.
ZTECorporationwillassumenoresponsibilityforconsequencesre-
sultingfromviolationofgeneralspecicationsforsafetyoperations
orofsafetyrulesfordesign,productionanduseofthedevices.
SafetySigns
Thecontentsthatusersshouldpayattentiontowhentheyinstall,
operateandmaintaindevicesareexplainedinthefollowingfor-
mats:
Warning:
Indicatesthemattersneedingcloseattention.Ifthisisignored,
seriousinjuryaccidentsmayhappenordevicesmaybedamaged.
CondentialandProprietaryInformationofZTECORPORATION1

ZXR108900SeriesUserManual(MPLSVolume)
Caution:
Indicatesthemattersneedingattentionduringconguration.
Note:
Indicatesthedescription,hint,tip,andsoonforcongurationop-
erations.
2CondentialandProprietaryInformationofZTECORPORATION

Chapter2
MPLSConfiguration
TableofContents
MPLSOverview..................................................................3
MPLSTerms.......................................................................7
LSPEstablishment..............................................................9
LabelControlandManagement...........................................13
ConguringMPLS..............................................................18
MPLSCongurationExamples.............................................21
MPLSMaintenanceandDiagnosis........................................25
MPLSOverview
MPLSFunction
Withtherapiddevelopmentofnetworkscaleandusernumber ,
peoplepaymoreattentiontotheproblemthathowtoextendser-
vicefurtheronthenetworkandhowtoimprovethequalityof
services.AstheIPprotocolisaconnectionlessprotocol,itishard
toprovideenoughthroughputsandtimedelayaccordingtothere-
quirements.ForIPprotocol,itjustusesbest-effortmechanismto
satisfytheusers.Withoutothermeasurestoimprovethecurrent
networkconditions,itishardtodevelopnewservicesgreatly.
Amongexistingnetworktechnologies,ATMhasadvantagesfor
qualityofservices.However ,thehighcostofATMnetworkmakes
ithardtoimplement.Inaddition,althoughATMswitchesare
widelyusedasbackbonenodesinnetworks,servicesthattake
ATMcellstodesktopdevelopveryslowly.
IPandATMtechnologiesmeetdifcultieswithrespectiveeld,and
theyneedeachothertohavefurtherdevelopment.Thereisin-
evitabilitytocombinethetwotechnologies.Therefore,Multi-Pro-
tocolLabelSwitching(MPLS)technologycomesintobeing.Itin-
tegratestheadvantagesofswitchingtechnologyinnetworkcore
andIProutingtechnologyinnetworkedge.
MPLSuseslabelswitching,soroutersonlyneedtojudgethelabels
whentheyforwardpackets.MPLSsupportsprotocolsinnetwork
layer(suchasIPv6,IPXandIP)aswellasprotocolsindatalink
layer(suchasATM,FRandPPP).
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ZXR108900SeriesUserManual(MPLSVolume)
IPForwardingFeatures
FeaturesoftraditionalIPforwardingisshowninFigure1.
FIGURE1IPFORWARDING
IPuseshop-by-hopmethodforcommunication.Whenapacket
reachesarouter ,therouterlooksupitsroutingtabletoforward
thepackettothenextrouter .Afterforwarding,thepacketisnot
controlledbytherouteranylonger .Whenthereiscorrectrouting
informationintheroutersalongthewholepath,thepacketscan
beforwardedcorrectly.
Whenlookinguptheroutingtable,therouterusesthelongest-
matchingprinciple.Therefore,itisdifculttoimplementfastfor-
warding.
Routershavetocollectinformationofdifferentnetworksegments
fordifferentroutingprotocols.Otherwise,theroutercannotfor-
wardthepackets.
IPnetworkisaconnectionlessnetwork,thereforeitsQoSisnot
wellensured.
ATMForwardingFeatures
ATMforwardingprocedureisshowninFigure2.
4CondentialandProprietaryInformationofZTECORPORATION

Chapter2MPLSConguration
FIGURE2ATMFORWARDING
ATMswitchesforwardpacketsthroughVPI/VCI.Theswitchesdo
notjudgeroutinginformationwhenforwardingATMcells.
WhenanATMswitchreceivesapacket,itlooksupVPI/VCItable
andforwardsthepacketsinswitchingway.
Whenforwardingpackets,ATMswitcheshavethefollowingfea-
tures:
�ATMchoosesthepathonthebaseofdatalinklayer .VPI/VCIis
effectiveforlocalswitch.Thefastlooking-upisimplemented
byhardware.
�ATMnetworkisaconnection-orientednetwork,soitcanim-
plementQoSaccordingtodifferentVPIs/VCIs.
�ATMsupportstrafccontrolmechanismanddifferentkindsof
services,suchasrealtimeservice.
MPLSFeatures
MPLSbelongstothethirdgenerationofnetworkarchitecture.It
isanewswitchingstandardofIPhigh-speedbackbonenetwork,
broughtforwardbyInternetEngineeringT askForce(IETF).
MPLSusessimpliedATMswitchingtechnologytoimplement
switchinginlayer2andlayer3.Itprovidesanidentierfor
eachIPmessage,andencapsulatestheidentiertoanewMPLS
messagetogetherwiththeIPmessage,decidingthetransmission
pathandpriorityoftheIPmessage.
ThedifferencesbetweenMPLSandtraditionalWANtechnology
areinthelabeldistributionmethodandlabelstackintroducedby
MPLS.InMPLS,theuseoflabelstackbringsnewapplications,such
astrafcengineering,VPNandFastRe-Routing(FRR).
BeforeforwardingtheIPpacketaccordingtocorrespondingpath,
theMPLSrouterreadstheheaderidentierofthemessageinstead
oftheIPaddressineachIPmessage.Therefore,thespeedto
CondentialandProprietaryInformationofZTECORPORATION5

ZXR108900SeriesUserManual(MPLSVolume)
forwardpacketsismuchfaster ,andMPLSiscalledalayer2.5
protocol,asshowninFigure3.
FIGURE3POSITIONOFMPLS
MPLScanusedifferentlayer2protocols.Tillnow,MPLStaskforce
hasimplementedstandardizationofidentiersusedinFR,ATM,
PPPlinkandIEEE802.3LANs.WhenMPLSrunsinFRandATM,
italsocarriesfreeconnectivityinIPnetworktotheseconnection-
orientatedtechnologies.
TheworkingmechanismofMPLSnetworkisthatitimplements
routingthroughIPoutsidetheMPLSnetworkandimplements
switchingthroughlookinguplabelswithinMPLSnetwork.
MPLShasthefollowingadvantages:
�MPLSprovidesconnection-orientatedservicesforIPnetwork.
�Integratedtechnologiesofdatalinklayerandnetworklayer ,
MPLSsolvestheproblemsaboutInternetextension,QoS.
�MPLSusesaccuratematchinginsteadofthelongest-match-
ingmethodtochoosepaththroughtheshortandxedlabels,
whichimprovesforwardingrate.
�WhensupportingIPservices,MPLSalsoprovideshighreliabil-
ityandQoSassurance.
�MPLSestablishesCR-LSPthroughexplicitroutingfunctionand
signalingprotocolswithQoSparameters,therefore,trafcen-
gineeringcanbeimplementedeffectively.
�MPLScansupportVPNwithlabelnestingtechnology.
MPLSWorkingPrinciple
InthenetworkoutsideMPLSdomain,packetsareforwardedintra-
ditionalIPforwardingway;whilewithintheMPLSdomain,packets
areforwardedbylabelswitching,asshowninFigure4.
6CondentialandProprietaryInformationofZTECORPORATION

Chapter2MPLSConguration
FIGURE4MPLSWORKINGPRINCIPLE
WithintheMPLSdomain,allroutersrunthelabeldistributionpro-
tocol,suchasLDPandRSVP .
TheprocedureofforwardinganIPpacketintheMPLSdomainis
describedasfollows:
1.TheingressLSRreceivestheIPpacket,andassignsalabelto
thispacketforidentication.
2.WhenthebackboneLSRsreceivethepacket,theylookuplabel
forwardingtables,anduseanewlabeltoreplacetheprimary
label.
3.WhenegressLSRreceivesthepacket,itremovesthelabeland
implementstraditionalIPforwarding.
MPLSTerms
MPLSLabel
Labelisaxed-lengthandlocallyeffectiveidentier .Itisusedto
identifyanFECthatagroupbelongstouniquely.Forexample,
whenloadbalanceiscongured,thesameFECmaycorrespondto
multiplelabels.However ,onlyonelabelstandsfortheFEC.The
structureisshowninFigure5.
FIGURE5MPLSLABELSTRUCTURE
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ZXR108900SeriesUserManual(MPLSVolume)
Alabelcontainsfourelds:
�Labeleld:20bitslong,usedtoforwardpointers.
�Expeld:3bitslong,reservedfordeningexperiments.
�Seld:1bitlong.MPLSsupportsmultiplelayersoflabels.
Whenthevalueofthiseldis1,itmeansthatthisentryis
alabelthatlocatesthebottomofthelabelstack.Whenthe
valueofthiseldis0,itmeansthatthisentryisalabelthat
locatesanypositionofthelabelstackexceptthebottom.
�TTLeld:8bitslong,usedforcodingtimetolive.
MPLSsupportsdifferentprotocolsindatalinklayer .MPLSlabelis
encapsulatedafterdatalinklayermessageandbeforelayer3data.
EachprotocolhasdifferentprotocolnumberdenedforMPLS.
InEthernetnetworks,MPLSpacketsareidentiedbyvalue0x8847
(forunicast)andvalue0x8848(formulticast).InPPP ,anewNCP,
MPLSCP ,isidentiedbyvalue0x8281.
TheSeldofalabelisshowninFigure6.InaMPLSdomain,a
messagecanbenestedwithmultiplelabels.
FIGURE6MPLSLABEL
Whenamessageisencapsulatedwithmultiplelabels,LSRdeals
themessagewithFirstInFirstOut(FIFO)rule.Thatis,LSRjust
forwardsthemessageaccordingtothetoplabel.
ForwardEquivalenceClass
ForwardEquivalenceClass(FEC)isarepresentationofagroupof
packetsthatsharethesamerequirementsfortheirtransport.All
packetsinsuchagroupareprovidedwiththesametreatment.
DuringlabelingbindingofLDP ,differentFECscorrespondtodiffer-
entlabels.EachnodeinMPLSdomainidentierstheFECtowhich
thepacketbelongsaccordingtothelabel.
Whentwogroupsofpacketswiththesamesourceaddressanddif-
ferentdestinationaddressesenteraMPLSdomain,MPLSjudges
thegroupsaccordingtoFECandMPLSndsthatthetwogroups
belongtotwoFECs.Therefore,MPLStreatsthegroupsindiffer-
entways,forexample,indifferentpathsandreservingdifferent
resources.Thetwogroupsareclassiedintodifferentclassesat
theingressoftheMPLSdomainandencapsulateddifferentlabels.
ThenodesintheMPLSdomainforwardthegroupsofpacketsac-
cordingtolabels.WhenthepacketsleavetheMPLSdomain,the
8CondentialandProprietaryInformationofZTECORPORATION

Chapter2MPLSConguration
egressLSRremovesthelabelsandforwardsthepacketstothe
destinations.
OpposedtoconventionalIPforwarding,inMPLS,theassignment
ofaparticularpackettoaparticularFECisdonejustonce.Itis
donewhenthepacketentersMPLSdomain.
MPLSNetworkStructure
ThestructureofMPLSnetworkisshowninFigure7.
FIGURE7MPLSNETWORKSTRUCTURE
LabelEdgeRouter(LER)isattheedgeofaMPLSdomain.LSR
assignslabelsforpacketsenteringMPLSdomain.Itimplements
functionssuchastrafcclassication,labelmappingandlabelre-
moving,LabelSwitchPath(LSP)initiation,IPpacketsforwarding
andDiff-Serv.
LabelSwitchRouter(LSR)isthecorerouterinaMPLSdomain.It
supportslabelswitchingandlabeldistributionfunctions.Itpartic-
ipatesinestablishingLSPandinitiatesnext-hopchange.
RoutersinMPLSdomainrunLabelDistributionProtocol(LDP)to
distributelabelsforpackets.
LSPEstablishment
ALSPisaforwardingpathestablishedaccordingtoMPLS.Itis
composedofLSRsandlinksfromsourceLSRtodestinationLSR,
whichissimilartovirtualcircuitofATM.
TherearethreedrivemodestoestablishaLSP:
�Packet-based
ThepackettrafcreachingaLSRspringslabeldistribution.In
thismode,thecostforlabeldistributionisdirectproportionto
thetrafc.Timedelayexistsforlabeldistribution.
�Topology-based
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ZXR108900SeriesUserManual(MPLSVolume)
Topology-baseddriveistodistributelabelsforcorresponding
routesofroutingprotocols.WhenaLSRdealswithrouteup-
dateofOSPForBGP ,theLSRmodiestheentriesinlabelfor-
wardingtable,meanwhiletheLSRdistributeslabelsforthese
entries.Aslongasthereisaroute,thelabelforthisrouteis
distributed.Therefore,thereisnotimedelaywhenLSRfor-
wardspackets.Thismodeiswidelyused.
�Application-based
Inthismode,LSRdistributeslabelsaccordingtocontrolservice
trafcwithnormalrequirements.Thecorrespondingprotocol
isRSVP .WhenaLSRdealswithRSVP ,theLSRmodiestheen-
triesinlabelforwardingtable,meanwhiletheLSRdistributes
labelsfortheseentries.Thismoderequiresapplicationpro-
gramsbringforwardlabelrequestandstreamruleinadvance
toobtainlabels.Italsodistributeslabelsforexistedroutes,
sothereisnotimedelay.However ,itisdifculttoimplement
RSVPinthewholenetwork,sothismodeisseldomused.
Comparingwithpacket-baseddrive,topology-baseddrivehasthe
followingadvantages:
�Labeldistributioncorrespondstocontrolmessage,therefore,
networkcostislittle.
�Labelisdistributedbeforetrafcarrives,sothereisnotime
delay.
TheprotocolsusedtodistributelabelsforLSRsarecalledsignalling
protocols.Commonsignallingprotocolsinclude:
�LabelDistributionProtocol(LDP)
�ConstrainedRouteLDP(CR-LDP)
�ResourceReservationProtocol-TrafcExtension(RSVP-TE)
�MultiprotocolBGP(MP-BGP)
LSPEstablishmentProcedure
InaMPLSdomain,LSPestablishmentprocedureisdescribedas
follows:
1.EachnoderunsdynamicroutingprotocolssuchasBGP,OSPF
andIS-IStogeneratearoutingtable.
2.Accordingtotheroutingtable,eachnodeestablishesaLabel
InformationBase(LIB)underthecontrolofLDP .
3.OutlabelsandinlabelsfromingressLSRtoegressLSRare
mappedtoformaLSP .
Thedetailedprocedureisdescribedasfollows:
Step1AsshowninFigure8,eachrouterrunsOSPFtogeneratearouting
table.RA,RBandRClearntheroute47.1.0.0/16toLER.
10CondentialandProprietaryInformationofZTECORPORATION

Chapter2MPLSConguration
FIGURE8GENERATINGAROUTETABLE
Step2AsshowninFigure9,theroutersrunLDPtodistributelabels.
FIGURE9GENERATINGALIB
AsanegressLSRto47.1.0.0/16,RCdistributesalabel“40”and
sendsittoupstreamneighborRB.Thisinformationisrecordedin
LIB.WhenRCreceivesamessagewithlabel“40”,itknowsthat
thismessageisto47.1.0.0/16.
WhenRBreceivesthebindinginformationof47.1.0.0/16andla-
bel“40”fromRC,itkeepsthelabelinformationandreceivingin-
terfaceinformationinLIB.Meanwhile,RBdistributesalabelfor
47.1.0.0/16andsendsthisinformationtoneighborsexceptthe
neighborconnectingtothereceivinginterface.SupposethatRB
sendsalabel“50”toRA.Therefore,thereissuchinformationin
LIBofRB,asshownbelow:
IntfInLabelInDestIntfOutLabelOut
15047.1.0.0240
Thisinformationmeans,whenRBreceivesamessagewithlabel
“50”frominterface1,itchangesthelabelto“40”andsendsthe
messagefrominterface2.RBdoesnotlookuprouteinitsrouting
table.
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ZXR108900SeriesUserManual(MPLSVolume)
WhenRAreceivesbindinginformation,RAactsinthesameway
asRBdoes.
LIBisalwaysisochronouswithroutingtables.Onceanewnon-
BGProuteisgeneratedintheroutingtable,LSRdistributesala-
belforthisroute.LSRdoesnotdistributelabelsforBGProutes.
Instead,itdistributesalabelforthenexthopofaBGProute.
Step3Aftertheinteractionoflabelsnishes,aLSPforms.WhenLSRs
forwardmessages,theyforwardthemaccordingtolabelsinstead
oflookinguproutingtables,asshowninFigure10.
FIGURE10GENERATINGALSP
WhenRAreceivesamessagewithdestinationaddress47.1.1.1,it
looksupitsroutingtablerst,andthenitlooksuplabelforwarding
table.WhenitndsthattheFEC47.1.0.0/16correspondstothe
label“50”,RAaddsthelabeltotheheaderofthemessage,and
sendsitfrominterface2.
WhenRBreceivesthemessagewithlabel“50”frominterface1,it
looksupthelabelforwardingtable,thenRAchangesthelabelto
“40”andsendsthemessagefrominterface2.
WhenRCreceivesthemessagewithlabel“40”frominterface1,it
looksupthelabelforwardingtable.RCndsthatthedestination
ofthemessageisanetworksegmentconnectingtoitselfdirectly.
Therefore,RCremovesthelabelandsendstheIPmessage.
PenultimateHopPopping
InaMPLSdomain,whentheegressLERreceivesmessagefromits
neighbor ,itlooksuplabelforwardingtablerstandremovesthe
label,thenitlooksuproutingtableandforwardstheIPmessage.
ThisdecreasestheperformanceoftheLERandincreasesforward-
ingcomplexity.Penultimatehoppoppingmechanismsolvesthis
problem.
Bydefault,LDPenablesonlypenultimatehoppoppingmechanism
fordirectroutesandaggregatedroutes.Fordirectroutes,LER
hastolookuproutingtabletogetnexthopinformationbeforeit
12CondentialandProprietaryInformationofZTECORPORATION