ospf pe-ce routing protocol overview, configuration and verification

16/8/2015 OSPFPECERoutingProtocolOverview,ConfigurationandVerification

http://fengnet.com/book/IOS_MPLS/ch05lev1sec1.html 1/47

OSPFPECERoutingProtocolOverview,ConfigurationandVerification

OpenShortestPathFirst(OSPF)PECEroutingprotocolsupportwasdevelopedforserviceprovidersofferingMPLSVPNservicestocustomerswhohavedeployedOSPFastheirintrasiteroutingprotocoland,hence,preferredusageofOSPFastheVPNintersiteroutingprotocolinanMPLSVPNenvironment.ForthcomingsectionsintroduceyoutotheissueswithimplementingtraditionalOSPFroutingmodelsinMPLSVPNenvironmentsandtheconceptoftheOSPFsuperbackbonetoresolvethem.Inaddition,theOSPFPECEroutingconfigurationinanMPLSVPNenvironmentandOSPFshamlinks,usedtoresolvesuboptimalroutingcausedbybackdoorlinksbetweenOSPFsitesinMPLSVPNenvironments,arediscussed.

TraditionalOSPFRoutingModel

ThetraditionalOSPFdomainisdividedintobackbone(Area0)andnonbackboneareaswherenonbackboneareasareconnectedtoArea0.Figure51showsCustomerAimplementingthetraditionalOSPFmodelinwhichnonbackboneareas,Area1andArea2belongingtoSite1andSite2,respectively,areconnectedtotheOSPFbackbonearea,Area0.

Figure51.TraditionalOSPFandMPLSVPNRoutingModel

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InanMPLSVPNenvironment,customernetworksareconnectedtoanMPLSVPNenabledproviderbackbone.AsshowninFigure51,CustomerAareas,Areas1and2,arenowconnectedtoanMPLSVPNenabledprovidernetwork.Area1andArea2haveroutersCE1AandCE2ArunningOSPFroutingprotocol.MPiBGPisusedbetweenPE1andPE2topropagateroutesbetweenSite1(Area1)andSite2(Area2).TraditionalOSPFBGPredistributionisperformedatPErouters,PE1andPE2.Figure51depictsthefollowingsequencethattakesplaceintraditionalOSPFBGPredistribution:

1. Network172.16.10.0/24isadvertisedtothePE1routerbyCE1AasaType1orType2linkstateadvertisement(LSA).



2. TraditionalOSPFBGProuteredistributiontakesplacewhere172.16.10.0/24isredistributedintoBGPatPE1.ThisrouteisthenpropagatedasaVPNv4routetoPE2.

3. AtPE2,theBGPVPNv4prefix172.16.10.0/24isredistributedinOSPF.

4. Thisredistributedroute172.16.10.0/24ispropagatedasanexternalLSAType5OSPFroute.

Therefore,theOSPFroutetype,orLSAtype,isnotpreservedwhentheOSPFroutefor172.16.10.0isredistributedintoBGPwhentraditionalOSPFroutingrulesareusedinanMPLSVPNenvironment.Moreover,thefollowingcharacteristicsofOSPFexternalroutesdonotallowasmoothtransitionforacustomertryingtomigratefromtraditionalOSPFroutingtotheMPLSVPNroutingmodel:

Internalroutes,regardlessoftheircost,arealwayspreferredoverexternalroutes.

Externalroutescannotbesummarized.

ExternalroutesarefloodedthroughoutallOSPFareas.

ExternalroutescoulduseadifferentmetrictypethatisnotcomparabletoOSPFcost.

ExternalLSAType5routesarenotinsertedinstubareasornotsostubbyareas(NSSA).

AnotherissueencounteredinOSPFimplementationswithMPLSVPNisthatthecustomercanhavemultiplesitesinArea0,asillustratedinFigure52,and,therefore,deviatefromthetraditionalOSPFhierarchyofsinglebackboneArea0withallnonbackboneareasconnectedtothisArea0.

Figure52.OSPFHierarchyIssue

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MPLSVPNorOSPFSuperbackboneConcept

TocircumventtheissuesposedbythetraditionalOSPFroutingmodel,theMPLSVPNarchitectureforOSPFPECEroutingwasexpandedtoallowtransparentcustomermigrationfromtraditionalOSPFroutingtotheMPLSVPNroutingmodelbyintroducinganotherbackboneabovetheOSPFArea0.ThisbackboneiscalledtheOSPForMPLSVPNsuperbackbone.

AsshowninFigure53

Figure53.MPLSVPNorOSPFSuperbackbone

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Thenonbackboneareas,Area1andArea2,aredirectlyconnectedtotheMPLSVPNsuperbackbonethatfunctionsasanOSPFArea0.Therefore,anactualArea0isnotrequiredasinthetraditionalOSPFdomain.Area0isarequirementonlywhenthePErouterisconnectedtotwodifferentnonbackboneareasbelongingtothesameOSPFdomainonaPErouter.

ThePErouters,PE1andPE2,whichconnectOSPFareasinthecustomerdomaintothesuperbackbone,appearasOSPFAreaBorderRouters(ABR)forthedevicesinthecustomerOSPFdomains.CEroutersCE1AandCE2AarenotawareofanyotherOSPFareasbeyondtheMPLSVPNsuperbackbonebecauseofitstransparency.

TheMPLSVPNsuperbackboneisimplementedusingMPiBGPbetweenPErouters.OSPFinformationiscarriedacrosstheMPLSVPNsuperbackboneusingBGPextendedcommunities.TheseextendedcommunitiesaresetandusedbyPErouters.

TherearenoOSPFadjacenciesorfloodingintheMPLSVPNsuperbackboneforcustomersitesconnectedtothesuperbackbone,exceptwhenusingOSPFshamlinks.

BGPExtendedCommunitiesforOSPFPECERouting

IntheMPLSVPNsuperbackbone,thefollowingBGPextendedattributesarecarried:

OSPFRouteType?PropagatesOSPFroutetypeinformationacrosstheMPiBGPbackbone.Figure54showstheOSPFroutetypeextendedcommunitiesattribute.Figure55depictstheOSPFroutetypedetailforprefix172.16.20.0,192.168.99.0,and192.168.199.0.

OSPFrouterID?IdentifiestherouterIDofthePEintherelevantVRFinstanceofOSPF.Thisaddressisnotpartoftheprovider'saddressspaceandisuniqueintheOSPFnetwork.

OSPFdomainID?IdentifiesthedomainofaspecificOSPFprefixintheMPLSVPNbackbone.Bydefault,thisvalueisequaltothevalueoftheOSPFprocessIDandcanbeoverwrittenbythecommanddomainIDipaddressundertheOSPFprocess.IfthedomainIDoftheroutedoesnotmatchthedomainIDonthereceivingPE,therouteistranslatedtotheexternalOSPFroute(LSAType5)withmetrictypeE2,assumingtheroutewasreceivedintheVRFtable.AllroutingbetweenOSPFdomainsisviaType5LSAs.

Figure54.OSPFRouteType,RouterID,andDomainID

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Figure55.OSPFRouteType,RouterID,andDomainIDDetailfor172.16.20.0,192.168.99.0,and192.168.199.0

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OSPFRoutePropagationUsingMPLSVPNSuperbackboneConcept

OSPFroutepropagationinanMPLSVPNenvironmentisnotastraditionalastheOSPFroutingmodelanddependsontheOSPFdomainID.Bydefault,theOSPFdomainIDisequaltotheprocessIDconfiguredonthePErouter.ThedomainIDissetintheVPNv4updatewhentheOSPFrouteisredistributedintoMPiBGP.

OSPFDomainIDIsSameonAllPERouters

Figure56showsanMPLSnetworkprovidingMPLSVPNservicestoCustomerA.CEroutersCE1AandCE2Aatsitenetworks172.16.10.0/24and172.16.20.0/24areinArea1andArea2,respectively,whilePECElinksatbothsitesareinArea0.OSPFprocessIDonbothPEroutersis101.Inaddition,CE2AfunctionsasatraditionalASBRbetweentheOSPFdomainandexternalroutingdomainsRIPv2andEIGRP(AS101).

Figure56.RoutePropagationWhenOSPFDomain(Process)IDIsSame

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ThefollowingsequencetakesplacewhenCE2Aissending172.16.20.0/24,209.165.127.0/27,and209.165.202.128/27toCE1A:

1. CE2AredistributesRIPv2network209.165.201.1intoOSPFandpropagatesitasanOSPFexternalType1route(OE1)toPE2AS1.EIGRPnetwork209.165.202.128/27isredistributedatCE2AandpropagatedasanOSPFexternalType2(OE2)toPE2AS1.CE2Aalsosends172.16.20.0/24asaninterarearoute(OIA)toPE2AS1.

2. VRFCust_AroutingtableonPE2AS1showsthereceivedroutes172.16.20.0/24asOSPFinterarearoutewithOSPFmetric(cost)74,209.165.127.0/27asanexternalType1routewithOSPFmetric84,and209.165.202.128/27routewithOSPFmetric20.

3. AsshowninFigure56,theOSPFcostfor172.16.20.0/24,209.165.127.0/27,and209.165.202.128/27iscopiedintoextendedBGPattributesasBGPMEDswhenOSPFisredistributedintoMPBGP.Theroutes172.16.20.0,209.165.127.0,and209.165.202.128/27arethenpropagatedtoPE1AS1viaMPiBGPsession.

4. PE1AS1receivestheBGPVPNv4routes172.16.20.0/24,209.165.127.0/27,and209.165.202.128/27fromPE2AS1andinsertsthemintheBGPtable.AsillustratedinFigure56,theOSPFmetricfortheroutesarenotalteredandremainthesamewhenpropagatedthoughtheMPBGPbackbone.

5. ThereceivingPErouter,PE1AS1,redistributestheMPBGProutesbackintoOSPF,verifiesthedomainID,andifthedomainIDoftheroutematchesthedomainIDonthereceivingPE,PE1AS1,itusestheoriginalLSAtypeandtheMEDattributetogenerateaninterareasummary(LSAType3)LSA.InFigure56,thedomainIDmatchesthedomainIDonPE1AS1,soPE1AS1reconstructstheoriginalupdateandupdatesthemetricbasedontheoutgoinginterfacesandpropagatesthe172.16.20.0/24asaninterarearoutetoCE1A.209.165.127.0/24and209.165.202.128/27arepropagatedasOSPFexternalType1andType2toCE1A.

6. CE1Areceivesthe172.16.20.0asaninterarearouteand209.165.127.0and209.165.202.128/27asOSPFexternalroutes.

OSPFDomainIDIsDifferentonAllPERouters

Aspreviouslymentioned,OSPFdomainIDbydefaultisequaltotheOSPFprocessIDconfiguredonPEroutersunlessmodifiedmanually.IftheprocessIDsaredifferentonPEroutersforsitesbelongingtosameVPN,OSPFroutesareseenasOSPFexternalroutes(Type5OSPFLSA).AsshowninFigure57,whenthePE1AS1routerinOSPFArea1usesOSPFprocessID201forSite1belongingtoVPNVPNA,andthePE2routerinOSPFArea2usesOSPFprocessID202forSite2belongingtoVPNVPNA,externalroutesareseenatSite1forSite2networksandviceversa.

Figure57.RoutePropagationWhenOSPFDomain(Process)IDIsDifferent

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ThefollowingsequenceofeventstakesplacewhenCE2Aissending192.168.20.0,192.168.99.0,and192.168.199.0toCE1A:

1. CE2BredistributesRIPv2network192.168.99.0intoOSPFandpropagatesitasanOSPFexternalType1route(OE1)toPE2AS1.EIGRPnetwork192.168.199.0/24isredistributedandpropagatedasanOSPFexternalType2(OE2)toPE2AS1.CE2Balsosends192.168.20.0/24asanintraarearoute(O)toPE2AS1.

2. VRFCust_BroutingtableonPE2AS1showsthereceivedroutes:192.168.20.0asanOSPFinterarearoutewithOSPFmetric74,192.168.99.0/24asanexternalType1routewithOSPFmetric84,and192.168.199.0/24ispreservedasanexternalType2routewithOSPFmetric20.

3. ThePErouter,PE2AS1,redistributestheOSPFroutes192.168.20.0,192.168.99.0,and192.168.199.0/27intoMPBGP,copiestheOSPFcostforthoseroutesintothemultiexitdiscriminator(MED)attribute,andsetstheBGPextendedcommunityroutetype(RT)toindicatetheLSAtypefromwhichtheroutewasderived,aswellastheextendedcommunityattributeOSPFdomainIDtoindicatetheprocessnumberofthesourceOSPFprocess.OSPFRTscarryinformationontheoriginalarea.TheLSAtypeandthetypeforexternalroutesaremetrictypes.

4. PE1AS1receivestheBGPVPNv4routes192.168.20.0,192.168.99.0,and192.168.199.0/27withthesamemetricinformationfromPE2AS1.TheinformationreceivedisinsertedintheBGPtable.Asshowninthefigure,theOSPFmetricfortheroutesarenotalteredandremainthesamewhenpropagatedthoughtheMPBGPbackbone.

5. PE2AS1checkstheattributesreceivedintheroute,and,becausethedomainIDoftheroutedoesnotmatchthedomainIDonthereceivingPE,therouteistranslatedtotheexternalType2route(LSAType5)OSPFroute.Inthiscase,thedomainIDmatchesthedomainIDonPE1AS1therefore,PE1AS1willreconstructtheoriginalupdateandupdatethemetricbasedontheoutgoinginterfacesandpropagate192.168.20.0asaninterarearoutetoCE1B.192.168.99.0and192.168.199.0/27arepropagatedasOSPFexternalType1andType2toCE1B.

6. CE1Breceivesthe192.168.20.0asaninterarearouteand192.168.99.0and192.168.199.0/24asOSPFexternalroutes.

ImpactofConfiguringOSPFDomainIDonPERouters

ManuallyconfiguringtheOSPFdomainIDchangesthebehaviorofroutesforLayer3VPNsconnectingmultipleOSPFdomains.ConfiguringdomainIDshelpscontrolLSAtranslation(forType3andType5LSAs)betweentheOSPFdomainsandbackdoorpaths.ThedefaultdomainIDis0.0.0.0.EachVPNroutingtableonaPErouterassociatedwithanOSPFroutinginstanceisconfiguredwiththesameOSPFdomainID.DomainIDsare,hence,usedtoidentifywhethertheroutesoriginatedfromtheOSPFdomainorfromexternalroutingprotocols.TheOSPFdomainIDhelpsidentifywhichOSPFdomainarouteoriginatedfrom,whichallowsclassificationofroutesasType3LSAsorType5LSAs.InFigure57,itisdifficulttoidentifywhichroutesreceivedonCE1AoriginatedwithinOSPForfromexternalroutingdomains.AsshowninFigure58,bymanuallyconfiguringthedomainIDtobethesameonPE1AS1andPE2AS1,wecancorrectlyidentifywhichroutesareexternalandwhichareinternal.



Figure58.RoutePropagationWhenOSPFDomain(Process)IDIsManuallyConfiguredtoBetheSame

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OSPFDownBitandDomainTag

RoutingloopscanoccurintheMPLSVPNenvironmentwhencustomeredgeroutersaredualhomedtotheserviceprovidernetwork.Figure59showsanMPLSVPNnetworkimplementingOSPFPECEroutingforCustomerAVPNAsites,Site1andSite2.Site2isinOSPFArea2andhasmultipleconnectionstotheproviderbackbone.

Figure59.RoutePropagation(OSPFDownBitNotSet)

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AsshowninFigure59,thefollowingsequencetakesplace,whichcanleadtoapotentialroutingloop:

1. CE1AsendsaType1routerorType2networkLSAtotheprovideredgerouter,PE1.

2. PE1routerreceivestheintraareaOSPFroutefromCE1AandredistributesitintoMPBGP.



3. ThereceivingPErouter,PE2,redistributestheMPBGProuteintoOSPFArea2asaninterareasummaryroute,LSAType3.

4. ThesummaryrouteispropagatedacrosstheOSPFareaandreceivedbytheotherPErouter,PE3,attachedtothesamearea,Area2.

5. PE3selectstheOSPFroute,becausetheadministrativedistanceoftheOSPFrouteisbetterthantheadministrativedistanceoftheMPiBGProute.PE3,therefore,redistributestherouteOSPFbackintotheMPBGPprocess,potentiallyresultinginaroutingloop.

OSPFDownBit

TheroutingloopshowninFigure59canbepreventedbytheuseoftheOSPFdownbit,whichispartoftheoptionsfieldintheOSPFheader.TheLSAheaderwiththeoptionfieldisshowninFigure510.

Figure510.LSAHeaderandOSPFDownBit

Figure511showshowtheOSPFdownbitisusedtopreventtheroutingloopshowninFigure510.

Figure511.RoutePropagationWhenOSPFDownBitIsSet

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ThefollowingistheroutepropagationwhentheOSPFdownbitisset:

1. CE1AsendsaType1routerorType2networkLSAtotheprovideredgerouter,PE1.

2. ThePE1routerreceivestheintraareaOSPFroutefromCE1AandredistributesitintoMPBGP.

3. ThereceivingPErouter,PE2,redistributestheMPBGProuteintoOSPFArea2asaninterareasummaryroute,LSAType3,withtheOSPFdownbitset.

4. ThesummaryroutewiththedownbitsetispropagatedacrosstheOSPFareaandreceivedbyPE3,whichisattachedtothesamearea,Area2.

5. WhenthePE3routerreceivesthesummaryLSAwiththedownbitset,itdoesnotredistributetheroutebackintoMPBGP.

OSPFRouteTagorVPNRouteTag

ThedownbithelpspreventroutingloopsbetweenMPBGPandOSPF,butnotwhenexternalroutesareannounced,suchaswhenredistributionbetweenmultipleOSPFdomainsorwhenexternalroutesareinjectedinanareathatisdualhomedtotheprovidernetwork.ThePErouterredistributesanOSPFroutefromadifferentOSPFdomainintoanOSPFdomainasanexternalroute.ThedownbitisnotsetbecauseLSAType5doesnotsupportthedownbit.TheredistributedrouteispropagatedacrosstheOSPFdomain.

AnonMPLSroutercanthenredistributetheOSPFrouteintoanotherOSPFdomain.TheOSPFrouteispropagatedthroughtheotherOSPFdomain,againwithoutthedownbit.APErouterreceivestheOSPFroute.Whenthedownbitismissing,therouteisredistributedbackintotheMPBGPbackbone,resultinginaroutingloop.ThisisshowninFigure512whenexternalroutesarepropagatedintotheVPNsites.

Figure512.ExternalRoutePropagationinDualHomedCE

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Thefollowingsequenceofstepstakesplace:

1. CE2AsendsaType5LSAfor209.165.201.0/27totheprovideredgerouter,PE2AS1.

2. ThePE2AS1routerreceivestheexternal(OE1)OSPFroutefromCE2AwiththeOSPFdownbitsetandthenredistributesitintoMPBGP.

3. AssumingthereceivingPErouterisPE1AS1,and,becauseitisredistributingtoadifferentOSPFdomain(201),PE1AS1clearstheOSPFdownbitandpropagatestheroutetoCE1Aasanexternal(OE1)route,LSAType5.

4. CE1AreceivestheroutewithouttheOSPFdownbitsetandpropagatestheexternalroutetoPE3AS1.

5. WhenthePE3AS1routerreceivestheexternalroutewithoutthedownbitset,itredistributestheroutebackintoMPBGP.

6. PE3AS1,therefore,propagatestheroutetoPE1AS1andPE2AS1,whichmightcausearoutingloop.

TheroutingloopsintroducedbyrouteredistributionbetweenOSPFdomainscanbesolvedwiththehelpofthetagfield,usingstandardBGPOSPFredistributionrules.AnonOSPFrouteisredistributedasanexternalOSPFroutebyaPErouter.Bydefault,thetagfieldissettotheBGPASnumber.TheredistributedrouteispropagatedacrosstheOSPFdomainwithoutthedownbitbutwiththetagfieldset.WhentherouteisredistributedintoanotherOSPFdomain,thetagfieldispropagated.AnotherPErouterreceivestheexternalOSPFrouteandfilterstheroutebasedonthetagfield.ThetagfieldmatchestheASnumbersotherouteisnotredistributedintoMPBGP.

ConfiguringandVerifyingOSPFPECERouting

TheconfigurationflowchartforimplementingOSPFPECEroutingisshowninFigure513.

Figure513.ConfigurationFlowchartforOSPFPECERouting

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Note

CiscoIOSversionspriorto12.3(4)T,12.0(27)S,and12.2(25)Shavethelimitationof32processesinwhichaseparateOSPFprocesshastobecreatedforeachVRFsothatthePEroutercanidentifytheOSPFroutesbelongingtothecorrectprocess.InanMPLSVPNenvironment,oneprocessisusedbyMPiBGP,onebyanIGProutingprotocol(OSPF,forexample),oneprocessforconnectedroutes,andanotherforstaticroutes.Therefore,outof32,only28processescouldbecreatedforVRFsusingOSPFPECEroutinguntiltheabovementionedversions.

ConfigurationScenario1OSPFProcessIDIsSameforCustomerAandDifferentforCustomerBVPNs

TheobjectiveofthissetupistounderstandhowtheOSPFprocessIDplaysapartindecidingthetypeofrouteseenoncustomeredgeroutersrunningOSPF.Figure514showsMPLSVPNservicesbeingprovidedtoCustomerAandCustomerBsites:

CustomerAnetwork?CustomerAhasCE1AandCE2AlocatedinthesameVPN,VPNA.TheyarepartofthesameOSPFdomain.PE1AS1andPE2AS1haveOSPFprocessID101configuredforVRFCust_AonPE1AS1andPE2AS1.

CustomerBnetwork?CustomerBhasCE1BandCE2BlocatedintheVPN,VPNB.PE1AS1andPE2AS1haveOSPFprocessIDsof201and202forCust_BVRFs,respectively.

Figure514.MPLSVPNNetworkImplementingOSPFPECERouting

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Beforeconfiguring,ensurethattheprovidernetworkisprovisionedtodeliverMPLSVPNservicestoCustomerAandBsites.EnsurethatIPaddressesarepreconfiguredandVRFsdefinedonPErouters.Example51providestheconfigurationfordefiningVRFanditsattributesonPEroutersforOSPFPECEroutingforVRFCust_A(CustomerA).

Example51.DefineVRFCust_AonPERoutersPE1AS1andPE2AS1

PE1AS1(config)#ipvrfCust_A

PE1AS1(configvrf)#rd1:100

PE1AS1(configvrf)#routetargetboth1:100

PE1AS1(config)#interfaceSerial1/0

PE1AS1(configif)#descriptionconnectedtoCE1A

PE1AS1(configif)#ipvrfforwardingCust_A

PE1AS1(configif)#ipaddress172.16.1.1255.255.255.252

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PE2AS1(config)#ipvrfCust_A

PE2AS1(configvrf)#rd1:100

PE2AS1(configvrf)#routetargetboth1:100

PE2AS1(config)#interfaceSerial1/0

PE2AS1(configif)#descriptionconnectedtoCE2A



ThestepstoconfigureOSPFPECEroutingonthePEroutersare

Step1. EnableperVRFOSPFRoutingEnableperVRFOSPFroutingforVRFCust_AonPEroutersPE1AS1andPE2AS1forCustomerAandCust_BonPE1AS1andPE2AS1forCustomerB.Example52illustratestheconfigurationforenablingOSPFroutingfortheVRFCust_A.

Example52.EnableperVRFOSPFRoutingforCust_AonPE1AS1andPE2AS1

PE1AS1(config)#routerospf101vrfCust_A

PE1AS1(configrouter)#routerid172.16.101.1

PE1AS1(configrouter)#network172.16.0.00.0.255.255area0

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PE2AS1(configrouter)#routerid172.16.102.1

PE2AS1(conigrouter)#network172.16.0.00.0.255.255area0

Step2. RedistributeOSPFRoutesinBGPInthisstep,theOSPFroutesreceivedfromthelocalCEroutersisredistributedinMPiBGP.Itisnecessarytoincludethematchcommandoptionotherwise,onlyOSPFinternalrouteswillberedistributedinBGP.Example53showstheproceduretoconfigureredistributionofOSPFroutesinBGP.

Example53.RedistributeOSPFRoutesinMPBGP

PE1AS1(config)#routerbgp1

PE1AS1(configrouter)#addressfamilyipv4vrfCust_A

PE1AS1(configrouteraf)#redistributeospf101vrfCust_Amatchinternal

external1external2

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PE2AS1(configrouteraf)#redistributeospf101vrfCust_Amatchinternal

external1external2

Step3. RedistributeMPIBGPinOSPFInthisstep,youredistributetheBGPVPNv4routesintoOSPFonPErouters,PE1AS1andPE2AS1.Ensurethatthesubnetskeywordisincludedwhenconfiguringredistributionotherwise,CiscoIOSredistributesonlythemajornetworksandsupernets.Example54showsthestepsonPE1AS1.RepeatthesamestepsonPE2AS1.

Example54.RedistributeMPIBGPinOSPF


PE1AS1(configrouter)#redistributebgp1subnets

________________________________________________________________


PE2AS1(configrouter)#redistributebgp1subnets

FinalConfigurationforProviderandEdgeRouters

Example55showstheconfigurationforPE1AS1,PE2AS1,andP1AS1.

Example55.PE1AS1,PE2AS1,andP1AS1Configuration

hostnamePE1AS1

!

ipcef

!

ipvrfCust_A

rd1:100

routetargetexport1:100

routetargetimport1:100

!

ipvrfCust_B

rd1:200





!

interfaceLoopback0

ipaddress10.10.10.101255.255.255.255

!

interfaceLoopback101

descriptionOSPFRouterIDforVRFCust_A

ipvrfforwardingCust_A

ipaddress172.16.101.1255.255.255.255

!


descriptionOSPFRouterIDforVRFCust_B

ipvrfforwardingCust_B

ipaddress192.168.201.1255.255.255.255

!

interfaceSerial0/0

descriptionconnectedtoP1AS1

ipaddress10.10.10.1255.255.255.252

mplsip

!

interfaceSerial1/0

descriptionconnectedtoCE1A


ipaddress172.16.1.1255.255.255.252

!

interfaceSerial2/0

descriptionconnectedtoCE1B


ipaddress192.168.1.1255.255.255.252

!



routerospf101vrfCust_A

routerid172.16.101.1

redistributebgp1subnets

network172.16.0.00.0.255.255area0

!

routerospf201vrfCust_B

routerid192.168.201.1


network192.168.0.00.0.255.255area1

!

routerospf1


network10.0.0.00.255.255.255area0

!

routerbgp1

nosynchronization

neighbor10.10.10.102remoteas1

neighbor10.10.10.102updatesourceLoopback0

noautosummary

!

addressfamilyvpnv4

neighbor10.10.10.102activate

neighbor10.10.10.102sendcommunityextended

exitaddressfamily

!

addressfamilyipv4vrfCust_B

redistributeospf201vrfCust_Bmatchinternalexternal1external2

noautosummary

nosynchronization

exitaddressfamily



!

addressfamilyipv4vrfCust_A

redistributeospf101vrfCust_Amatchinternalexternal1external2

noautosummary

nosynchronization

exitaddressfamily

__________________________________________________________________________

hostnamePE2AS1

!

ipcef

!

ipvrfCust_A

rd1:100



!

ipvrfCust_B

rd1:200



!

interfaceLoopback0

ipaddress10.10.10.102255.255.255.255

!


descriptionOSPFRouterIDforVRFCust_A


ipaddress172.16.102.1255.255.255.255

!




descriptionOSPFRouterIDforVRFCust_B


ipaddress192.168.202.1255.255.255.255

!

interfaceSerial0/0


ipaddress10.10.10.5255.255.255.252

mplsip

!

interfaceSerial1/0



ipaddress172.16.2.1255.255.255.252

!

interfaceSerial2/0



ipaddress192.168.2.1255.255.255.252

!




network172.16.0.00.0.255.255area0

!

routerospf202vrfCust_B

routerid192.168.202.1


network192.168.0.00.0.255.255area2

!

routerospf1




network10.0.0.00.255.255.255area0!

routerbgp1

nosynchronization



noautosummary

!

addressfamilyvpnv4


neighbor10.10.10.101sendcommunityextended

exitaddressfamily

!

addressfamilyipv4vrfCust_B

redistributeospf202vrfCust_Bmatchinternalexternal1external2

noautosummary

nosynchronization

exitaddressfamily

!



noautosummary

nosynchronization

exitaddressfamily

___________________________________________________________________________

hostnameP1AS1

!

interfaceLoopback0

ipaddress10.10.10.200255.255.255.255

!



interfaceSerial0/0

descriptionconnectedtoPE1AS1

ipaddress10.10.10.2255.255.255.252

mplsip

!

interfaceSerial1/0


ipaddress10.10.10.6255.255.255.252

mplsip

!

routerospf1

logadjacencychanges

network10.0.0.00.255.255.255area0

Example56showstheconfigurationforCE1A,CE2A,CE1B,andCE2B.

Example56.CE1A,CE2A,CE1B,andCE2BConfiguration

hostnameCE1A

!

interfaceEthernet0/0

descriptionVPNASite1network

ipaddress172.16.10.1255.255.255.0

!

interfaceSerial1/0


ipaddress172.16.1.2255.255.255.252

!

routerospf101

network172.16.1.00.0.0.255area0

network172.16.10.00.0.0.255area1

__________________________________________________________________________



hostnameCE2A

!

interfaceLoopback0

descriptionRIPv2network

ipaddress209.165.201.1255.255.255.224

!

interfaceLoopback1

descriptionEIGRPnetwork

ipaddress209.165.202.129255.255.255.224

!



ipaddress172.16.20.1255.255.255.0

!

interfaceSerial1/0


ipaddress172.16.2.2255.255.255.252

!

routereigrp1

network209.165.202.0

noautosummary

!

routerospf101

redistributeeigrp1subnets

redistributeripmetrictype1subnets

network172.16.2.00.0.0.255area0

network172.16.20.00.0.0.255area2

!

routerrip

version2



redistributeospf101matchinternalexternal1external2

network209.165.201.0

noautosummary

__________________________________________________________________________

hostnameCE1B

!


descriptionVPNBSite1network

ipaddress192.168.10.1255.255.255.0

!

interfaceSerial1/0


ipaddress192.168.1.2255.255.255.252

!

routerospf201

network192.168.1.00.0.0.255area1

network192.168.10.00.0.0.255area1

__________________________________________________________________________

hostnameCE2B

!

interfaceLoopback0

ipaddress192.168.99.1255.255.255.0

!

interfaceLoopback1

ipaddress192.168.199.1255.255.255.0

!


descriptionVPNBSite2network

ipaddress192.168.20.1255.255.255.0

!



interfaceSerial1/0


ipaddress192.168.2.2255.255.255.252

!

routereigrp1

redistributeospf202metric1500125511500matchinternalexternal1external2

network192.168.199.0

noautosummary

!

routerospf202

redistributeeigrp1subnets

redistributeripmetrictype1subnets

network192.168.2.00.0.0.255area2

network192.168.20.00.0.0.255area2

!

routerrip

version2

redistributeospf202metric1matchinternalexternal1external2

network192.168.99.0

noautosummary

VerifyOSPFPECERouting

ThestepstoverifyOSPFPECEroutingareasfollows:

Step1. VerifyOSPFneighboradjacencyThisstepensuresthatthereisanOSPFneighborrelationshipandadjacencyisformedbetweentheprovideredge(PE)routerandcustomeredge(CE)router.Example57showstheoutputonthePEandCErouterwheretheadjacencyisformed,indicatedbytheFULLstate.

Example57.showipospfneighboronPE1AS1andPE2AS1

PE1AS1#showipospfneighbor

NeighborIDPriStateDeadTimeAddressInterface



10.10.10.2000FULL/00:00:3810.10.10.2Serial0/0

192.168.10.10FULL/00:00:35192.168.1.2Serial2/0

172.16.10.10FULL/00:00:32172.16.1.2Serial1/0

____________________________________________________________________________



10.10.10.2000FULL/00:00:3910.10.10.6Serial0/0

192.168.20.10FULL/00:00:38192.168.2.2Serial2/0

172.16.20.10FULL/00:00:32172.16.2.2Serial1/0

Step2. VerifyroutepropagationforCustomerAThesestepsverifyroutepropagationfor192.168.20.0,192.168.99.0,and192.168.199.0.

Example58showstheCust_AVRFroutingtablewhere172.16.10.0isreceivedasanintraareaOSPFroute.209.165.201.0/27and209.165.201.128/27showupasOSPFexternalType1andType2routes,respectively.

Example58.showiproutevrfCust_Aospf101onPE2AS1

PE2AS1#showiproutevrfCust_Aospf101

172.16.0.0/16isvariablysubnetted,6subnets,3masks

OIA172.16.20.0/24[110/74]via172.16.2.2,01:14:00,Serial1/0

209.165.201.0/27issubnetted,1subnets

OE1209.165.201.0[110/84]via172.16.2.2,01:14:00,Serial1/0


OE2209.165.202.128[110/20]via172.16.2.2,01:14:00,Serial1/0

Cust_AOSPFroutesareredistributedinMPiBGP,andtheOSPFmetricsfor172.16.20.0,209.165.127.0,and209.165.202.128/27arecopiedintoextendedBGPattributesasBGPMEDs.Theroutes172.16.20.0/24,209.165.201.0/27,and209.165.202.128/27arethenpropagatedtoPE1AS1viaMPiBGPsession.Example59displaysoutputoftheshowipbgpvpnvrfCust_AcommandonPE2AS1.Example510displaysoutputoftheshowipbgpvpnv4all172.16.20.0commandonPE2AS1.

Example59.showipbgpvpnvrfCust_AonPE2AS1

PE2AS1#showipbgpvpnvrfCust_A

NetworkNextHopMetricLocPrfWeightPath

RouteDistinguisher:1:100(defaultforvrfCust_A)



*>172.16.20.0172.16.2.27432768?

*>209.165.201.0172.16.2.28432768?

*>209.165.202.128172.16.2.22032768?

Example510.showipbgpvpnv4all172.16.20.0onPE2AS1

PE2AS1#showipbgpvpnv4all172.16.20.0

BGProutingtableentryfor1:100:172.16.20.0/24,version138

Paths:(1available,best#1,tableCust_A)

Advertisedtoupdategroups:

1

Local

172.16.2.2from0.0.0.0(10.10.10.102)

Originincomplete,metric74,localpref100,weight32768,valid,sourced,best

ExtendedCommunity:RT:1:100OSPFDOMAINID:0x0005:0x000000650200

OSPFRT:0.0.0.0:3:0OSPFROUTERID:172.16.102.1:512,

mplslabelsin/out34/nolabel

AtPE1AS1,theroutesarereceivedwithmetricsunchangedfromtheiroriginationatPE2AS1.PE1AS1redistributestheMPBGProutebackintoOSPF,verifiesthedomainID,and,ifthedomainIDoftheroutematchesthedomainIDonPE1AS1,itusestheoriginalLSAtypeandtheMEDattributetogenerateaninterareasummary(LSAType3)LSAotherwise,itgeneratesanexternalroute.Inthiscase,theOSPFdomainIDmatches,and172.16.20.0isgeneratedasaninterarearoutetoCE1A,andthemetricismodifiedto138(74[originalmetric]+64[outgoinginterfacecostonPE1AS1toCE1A,inthiscase,seriallink=64]).Example511displaysoutputfromtheshowipbgpvpnv4vrfCust_AonPE1AS1.Example512displaysoutputfromtheshowiprouteospfcommandonCE1A.

Example511.showipbgpvpnv4vrfCust_AonPE1AS1

PE1AS1#showipbgpvpnv4vrfCust_A

NetworkNextHopMetricLocPrfWeightPath

RouteDistinguisher:1:100(defaultforvrfCust_A)

*>172.16.1.0/300.0.0.0032768?

*>i172.16.2.0/3010.10.10.10201000?

*>172.16.10.0/24172.16.1.27432768?

*>i172.16.20.0/2410.10.10.102741000?

*>172.16.101.1/320.0.0.0032768?



*>i172.16.102.1/3210.10.10.10201000?

*>i209.165.201.0/2710.10.10.102841000?

*>i209.165.202.128/27

10.10.10.102201000?

Example512.showiprouteospfonCE1A

CE1A#showiprouteospf


OIA172.16.20.0/24[110/138]via172.16.1.1,01:15:26,Serial1/0

OIA172.16.2.0/30[110/65]via172.16.1.1,01:15:26,Serial1/0

O172.16.101.1/32[110/65]via172.16.1.1,01:16:13,Serial1/0

OIA172.16.102.1/32[110/65]via172.16.1.1,01:15:26,Serial1/0


OE1209.165.201.0[110/148]via172.16.1.1,01:15:21,Serial1/0


OE2209.165.202.128[110/20]via172.16.1.1,01:15:21,Serial1/0

Step3. VerifyroutepropagationforCustomerBThesestepsverifyroutepropagationfor192.168.20.0,192.168.99.0,and192.168.199.0.

Example513showstheCust_BVRFroutingtablewhere192.168.20.0isreceivedasanintraareaOSPFroute.192.168.99.0and192.168.199.0arereceivedasOSPFE1andE2routes,respectively.

Example513.showiproutevrfCust_Bospf202onPE2AS1

PE2AS1#showiproutevrfCust_Bospf202

OE2192.168.199.0/24[110/20]via192.168.2.2,00:39:02,Serial2/0

OE1192.168.99.0/24[110/84]via192.168.2.2,00:39:02,Serial2/0

O192.168.20.0/24[110/74]via192.168.2.2,00:39:02,Serial2/0

Cust_BOSPFroutesareredistributedinMPiBGP,andtheOSPFmetricsfor192.168.20.0,192.168.99.0,and192.168.199.0arecopiedintoextendedBGPattributesasBGPMEDs.TheroutesarethenpropagatedtoPE1AS1viaMPiBGPsession.Example514displaysoutputfromtheshowipbgpvpnv4all|begin192.168.20.0commandonPE2AS1.Example515displaysoutputfromtheshowipbgpvpnv4all192.168.99.0commandonPE2AS1.



Example514.showipbgpvpnv4all|begin192.168.20.0onPE2AS1

PE2AS1#showipbgpvpnv4all|begin192.168.20.0

*>192.168.20.0192.168.2.27432768?

*>192.168.99.0192.168.2.28432768?

*>192.168.199.0192.168.2.22032768?


PE2AS1#showipbgpvpnv4all192.168.99.0

BGProutingtableentryfor1:200:192.168.99.0/24,version145

Paths:(1available,best#1,tableCust_B)

Advertisedtoupdategroups:

1

Local

192.168.2.2from0.0.0.0(10.10.10.102)

Originincomplete,metric84,localpref100,weight32768,valid,sourced,best

ExtendedCommunity:RT:1:200OSPFDOMAINID:0x0005:0x000000CA0200

OSPFRT:0.0.0.0:5:0OSPFROUTERID:192.168.202.1:512,

mplslabelsin/out28/nolabel

AtPE1AS1,theroutesarereceivedwithmetricsunchanged.PE1AS1redistributestheMPBGProutesbackintoOSPF,verifiesthedomainID,and,ifthedomainIDoftheroutematchesthedomainIDonPE1AS1,itusestheoriginalLSAtypeandtheMEDattributetogenerateaninterareasummary(LSAType3)LSAotherwise,itgeneratesanexternalroute.Inthiscase,theOSPFdomainIDdoesnotmatch,so192.168.20.0isgeneratedasanexternalroute.Example516displaysoutputfromtheshowipbgpvpnv4all|begin192.168.20.0commandonPE1AS1.Example517displaysoutputfromtheshowiprouteospfcommandonCE1B.


PE1AS1#showipbgpvpnv4all|begin192.168.20.0

*>i192.168.20.010.10.10.102741000?

*>i192.168.99.010.10.10.102841000?

*>i192.168.199.010.10.10.102201000?

Example517.showiprouteospfonCE1B



CE1B#showiprouteospf

OE2192.168.199.0/24[110/20]via192.168.1.1,00:48:46,Serial1/0


O192.168.201.1[110/65]via192.168.1.1,00:49:33,Serial1/0

OE2192.168.99.0/24[110/84]via192.168.1.1,00:48:46,Serial1/0

OE2192.168.20.0/24[110/74]via192.168.1.1,00:48:46,Serial1/0


OE2192.168.202.1[110/1]via192.168.1.1,00:48:46,Serial1/0


OE2192.168.2.0[110/1]via192.168.1.1,00:48:46,Serial1/0

ConfigurationScenario2UsingOSPFDomainIDSupportforLSAType5/Type3Translation

Figure515showsanMPLSVPNnetworkforCustomerBinwhichCE1BandCE2BbelongtothesameVPNbuthavedifferentprocessIDs.ConfiguringdomainIDshelpscontrolLSAtranslation(forType3andType5LSAs)betweentheOSPFdomainsandbackdoorpaths.EachVPNroutingtableinaPErouterassociatedwithanOSPFroutinginstanceisconfiguredwiththesameOSPFdomainID.

Figure515.MPLSVPNNetworkUsingDomainIDSupport

[Viewfullsizeimage]

ConfigurationforthissectionremainsthesameasshowninconfigurationScenario1.ConfiguringdomainIDipaddressunderthe



OSPFroutingprocessforVRFCust_Bistheonlyadditioninthissection.Theconfigurationstepisoutlinedhere:

ConfigureOSPFdomainID?ConfiguredomainIDipaddressundertheOSPFroutingprocessforCust_B.ThedomainIDhastobecommonforallPEroutersforthatVPNinstance.Useloopback202onPE2asthedomainIDforCustomerB.Example518showshowtoconfiguretheOSPFdomainID.

Example518.ConfiguringOSPFDomainID

PE1AS1(config)#routerospf201vrfCust_B

PE1AS1(configrouter)#domainID192.168.202.1

__________________________________________________________________________

PE2AS1(config)#routerospf202vrfCust_B

PE2AS1(configrouter)#domainID192.168.202.1

VerifyRoutePropagationWhenUsingOSPFDomainID

Example519showsthatwhentheOSPFdomainIDisnotconfigured,theCE1Broutingtableshowsalltheroutesbeingexternal.

Example519.RoutingTableonCE1BWhenOSPFDomainIDIsNotConfigured


OE2192.168.199.0/24[110/20]via192.168.1.1,00:00:08,Serial1/0


O192.168.201.1[110/65]via192.168.1.1,00:00:14,Serial1/0

OE2192.168.99.0/24[110/84]via192.168.1.1,00:00:08,Serial1/0

OE2192.168.20.0/24[110/74]via192.168.1.1,00:00:08,Serial1/0


OE2192.168.202.1[110/1]via192.168.1.1,00:00:14,Serial1/0


OE2192.168.2.0[110/1]via192.168.1.1,00:00:14,Serial1/0

Example520showsthatwhentheOSPFdomainIDisconfigured,theCE1Broutingtableshows192.168.20.0asinterareaand192.168.99.0asexternalType1.

Example520.RoutingTableonCE1BWhenOSPFDomainIDIsConfigured


OE2192.168.199.0/24[110/20]via192.168.1.1,00:44:09,Serial1/0




O192.168.201.1[110/65]via192.168.1.1,00:45:15,Serial1/0

OE1192.168.99.0/24[110/148]via192.168.1.1,00:44:09,Serial1/0

OIA192.168.20.0/24[110/138]via192.168.1.1,00:44:14,Serial1/0


OE2192.168.202.1[110/1]via192.168.1.1,00:44:09,Serial1/0


OE2192.168.2.0[110/1]via192.168.1.1,00:44:09,Serial1/0

OSPFShamLinks

Figure516showsanMPLSenabledserviceprovidernetworkprovidingMPLSVPNservicestoCustomerAsitesbelongingtothesameVPN,VPNA.

Figure516.MPLSVPNNetworkUsingBackdoorLink

[Viewfullsizeimage]

CustomerAhasfoursitesinVPNA.AllsitesareintheOSPFarea,Area0.Site3andSite4inOSPFArea0areconnectedbyalowbandwidthbackdoorlink(512kbps).ThebackdoorlinkprovidesconnectivitybetweenSite3andSite4whenthelinktotheproviderbackboneisdownordisconnected.ThesitesarealsoconnectedtothehighbandwidthBGPbasedMPLSVPNbackbone.Thistypeofsituationcanresultinsuboptimalrouting,asshowninFigure517.

Figure517.SuboptimalRoutinginMPLSVPNNetworkUsingBackdoorLink

[Viewfullsizeimage]



Thefollowingsequencetakesplacewhen172.16.40.0/24ispropagatedbyCE4AtoCE3A:

1. CE4AsendsaType1LSAfor172.16.40.0/24totheprovideredgerouter,PE2AS1andCE3A.

2. ThePE2AS1routerreceives172.16.40.0/24asanintraarearoute.ItredistributesintoMPBGP.

3. PE1AS1redistributes172.16.40.0/24intoOSPFandpropagates172.16.40.0/24asaninterarearoutetoCE3A.

4. CE3Areceivesthe172.16.40.0/24asaninterarearoutefromPE1AS1andasanintraarearoutefromCE4A.InOSPF,intraarearoutesarepreferredoverinterarearoutestherefore,CE3ApreferstheintraarearoutefromCE4AandinsertsitintheOSPFdatabase.

Thissequenceofeventsalsooccurswith172.16.20.0/24,whichispropagatedbyCE2A.Therefore,datapacketsoriginatingfromthe172.16.30.0network(Site3)to172.16.40.0(Site4)willtakethebackdoorlink.Thisalsoappliestotrafficoriginatingfrom172.16.10.0(Site1)to172.16.20.0(Site2)becauseanyalternativeroutesfromtheMPLSVPNbackbonewouldbeinterarearoutes,andintraarearoutesarepreferred.Thetrafficforwardingis,therefore,consideredsuboptimalbecausethebackdoorlinkhaslowbandwidthandisintendedforbackup.Figure518showsthedataforwardingpathinanMPLSVPNnetworkusingabackdoorlink(noshamlinks).

Figure518.DataForwardingPathinMPLSVPNNetworkUsingBackdoorLink

[Viewfullsizeimage]



Thissituationcanbeavoidedbyusingashamlink.Ashamlinkisalogicallinkthatbelongstothearea(intraarea)butiscarriedbytheBGPbasedsuperbackbone.ThetwoPErouterswillbetheendpointsoftheshamlink.TheywillformanOSPFadjacencyacrossitandfloodintraareaLSAsviathislink.ThetwositesthatbelongtoArea0canhaveashamlinkbetweenthemandthenreceiveintraareaOSPFroutesviathebackdoorlinkortheshamlink.Whentheshamlinkisup,itisregardedasanunnumberedpointtopointOSPFlinkintheareabelongingtotheVPNsites.Theshamlinkistreatedasademandcircuit(DC)bytheOSPFinordertoreducethetrafficflowovertheshamlink.ThisimpliesthattheregularLSAwillfloodovertheshamlinkbuttheperiodicrefreshtrafficisavoided.Figure519showsashamlink.

Figure519.ShamLink

[Viewfullsizeimage]

CE4Asends172.16.40.0/24asLSAType1toCE3A,whichthenpropagatestheLSAtothePE1AS1router.ThePE1AS1routerhasnowreceivedtheOSPFLSAType1routefromtwodirectionsfromCE4AviaCE3AandfromPE2AS1viatheOSPFshamlink.



OSPFshamlinkservesasanintraarealinkbetweenPE1AS1andPE2AS1.TheOSPFcostoftheshamlinkcanbeconfiguredsothatitwillbelowerthanthecostofthebackuplinkbetweenCE3AandCE4A.ThePE2AS1routerthereforeredistributestheOSPFroute172.16.40.0/24intoMPBGPbecausetheOSPFroutewasnotreceivedviaashamlinkfromPE1AS1.ThePE1AS1routeralsodoesnotredistributetherouteinMPiBGPbecausetheroutewasreceivedfromPE2AS1viatheOSPFshamlinkbetweenPE1AS1andPE2AS1.PE1AS1thereforeinstallstheOSPFroutereceivedovertheshamlinkinitsVRFroutingtable.TheLSAforroute172.16.40.0/24isthenpropagatedintoSite3toallowCE3Atoselectthebestpath.PacketsreceivedfromtheSite4will,therefore,beroutedacrosstheMPLSVPNbackboneandwillusethehighbandwidthlink.Also,theCE3ArouteratSite3selectstheshamlinkasthebestpathtoreach172.16.40.0/24.Therefore,thetrafficbetweenSite3andsite4isoptimallyroutedviathelowcostshamlinkbetweenPE1AS1andPE2AS1.

ConfigurationFlowchartforOSPFShamLinks

Figure520showstheconfigurationflowcharttoconfigureOSPFshamlinks.

Figure520.ConfigurationFlowcharttoConfigureOSPFShamLinks

[Viewfullsizeimage]

ConfigurationScenario3OSPFShamLinks

Inthissection,youusetheMPLSVPNsetupshowninFigure517.Beforeconfiguring,ensurethattheprovidernetworkisprovisionedtodeliverMPLSVPNservicestoCustomerAsites.EnsurethatIPaddressesarepreconfiguredandVRFsaredefinedonPErouters.

ToconfigureOSPFshamlinks,followthesesteps:

Step1. CreateendpointsoftheshamlinkThefirststepistocreatetheendpointsoftheshamlinkbycreatingaloopbackinterfaceoneachPErouterandassociatingittotheVRFCust_AoftheVPN.ThisassociatestheshamlinkintheVRFCust_AfortheVPNsite.TheaddressoftheloopbackinterfaceshouldbeanaddressintheVPN'saddressspace,nottheMPLSVPNserviceprovider'saddressspacebecausetheshamlinkisconsideredalinkoftheVPNcustomerandnottheMPLSVPNserviceprovider's.Example521showsthisconfigurationonthePE1AS1andPE2AS1.

Example521.CreateEndpointsoftheShamLink

PE1AS1(config)#interfaceLoopback101

PE1AS1(configif)#descriptionshamlinkEndpointonPE1AS1



________________________________________________________________

PE2AS1(config)#interfaceLoopback101



PE2AS1(configif)#descriptionshamlinkEndpointonPE2AS1



Step2. RedistributetheendpointsinMPBGPRedistributetheshamlinkendpointscreatedinStep1inBGP.ThisensuresthatthePEroutershavereachabilitytotheendpoints.Whentheshamlinkendpointiscreated,itisnecessarytoensurethateachPErouterhasreachabilitytotheendpoint.SuchreachabilityinformationmustbelearnedviaBGPineachPErouter,whichcanbedonebyredistributingtheendpointaddressestoMPBGP,asshowninExample522.

Note

TheendpointaddressinformationshouldnotbeadvertisedviaOSPFitself.TheloopbackinterfaceshouldnotbeincludedintheOSPF101VRFprocess.ItwouldcauseaproblemwhenabackdoorpathexistsbetweenthetwoVPNsites.Insuchascenario,thePErouterthatincludestheendpointaddressintheOSPFVRFprocesswouldexchangetheendpointaddressinformationviaOSPFtotheCEroutersinLSAType1or2.TheLSAwouldthenpropagatetotheothersideofPErouteroverthebackdoorpath.AlthoughtheothersideofthePEwouldalsoreceivetheendpointaddressinformationviaMPBGP,itwillprefertheOSPFrouteratherthantheBGPlearnedroutebecauseoftheadministrativedistancevalue.TheshamlinkwillfailtobeupbecausetheendpointaddressinformationisnotlearnedviaBGP.Example522showshowtoredistributetheendpointsinMPBGP.

Example522.RedistributetheEndpointsinMPBGP



PE1AS1(configrouteraf)#redistributeconnected

________________________________________________________________



PE2AS1(configrouteraf)#redistributeconnected

Step3. EnableshamlinkunderOSPFVRFprocessConfiguretheshamlinkundertheOSPFprocess.BecausetheshamlinkisconsideredanOSPFlinkwithintheareaoftheVPNsites,theareaIDneedstobespecifiedtomatchtheVPNsites'areaID,andacostvalueneedstobeassignedtoit.Whenthereisabackdoorconnection,thecostassignedcandeterminewhetherthetrafficflowsbetweenthebackdoorlinkandtheshamlink.Example523showsthesteponPE1AS1.RepeatthesamesteponPE2AS1.

Example523.EnableShamLinkUnderOSPFVRFProcess


PE1AS1(configrouter)#area0shamlink172.16.101.1172.16.102.1cost1

________________________________________________________________________




PE2AS1(configrouter)#area0shamlink172.16.102.1172.16.101.1cost1

FinalConfigurationforPE1AS1andPE2AS1

Example524showstheconfigurationonPE1AS1andPE2AS1.

Example524.ConfigurationonPE1AS1andPE2AS1

hostnamePE1AS1

!

ipcef

!

ipvrfCust_A

rd1:100



!

interfaceLoopback0

ipaddress10.10.10.101255.255.255.255

!


descriptionshamlinkEndpointonPE1AS1


ipaddress172.16.101.1255.255.255.255

!

interfaceSerial0/0


ipaddress10.10.10.1255.255.255.252

mplsip

!

interfaceSerial1/0





ipaddress172.16.1.1255.255.255.252

!

interfaceSerial2/0



ipaddress172.16.3.1255.255.255.252

!



area0shamlink172.16.101.1172.16.102.1


network172.16.1.00.0.0.255area0

network172.16.3.00.0.0.255area0

!

routerospf1


network10.0.0.00.255.255.255area0

!

routerbgp1

nosynchronization

redistributeeigrp101



noautosummary

!

addressfamilyvpnv4


neighbor10.10.10.102sendcommunityboth

exitaddressfamily



!


redistributeconnected


noautosummary

nosynchronization

exitaddressfamily

__________________________________________________________________________

hostnamePE2AS1

!

ipcef

!

ipvrfCust_A

rd1:100



!

interfaceLoopback0

ipaddress10.10.10.102255.255.255.255

!


descriptionshamlinkEndpointonPE2AS1


ipaddress172.16.102.1255.255.255.255

!

interfaceSerial0/0


ipaddress10.10.10.5255.255.255.252

mplsip

!



interfaceSerial1/0



ipaddress172.16.2.1255.255.255.252

!

interfaceSerial2/0



ipaddress172.16.4.1255.255.255.252

!



area0shamlink172.16.102.1172.16.101.1


network172.16.2.00.0.0.255area0

network172.16.4.00.0.0.255area0

!

routerospf1


network10.0.0.00.255.255.255area0

!

routerbgp1

nosynchronization



noautosummary

!

addressfamilyvpnv4


neighbor10.10.10.101sendcommunityboth



exitaddressfamily

!


redistributeconnected


noautosummary

nosynchronization

exitaddressfamily

FinalConfigurationforCE1A,CE2A,CE3A,andCE4A

Example525showstheconfigurationsonCE1A,CE2A,CE3A,andCE4A.

Example525.ConfigurationsonCE1A,CE2A,CE3A,andCE4A

hostnameCE1A

!



ipaddress172.16.10.1255.255.255.0

!

interfaceSerial1/0


ipaddress172.16.1.2255.255.255.252

!

routerospf101

network172.16.0.00.0.255.255area0

_________________________________________________________________________

hostnameCE2A

!


ipaddress172.16.20.1255.255.255.0



!

interfaceSerial1/0


ipaddress172.16.2.2255.255.255.252

!

routerospf101

network172.16.0.00.0.255.255area0

_________________________________________________________________________

hostnameCE3A

!


ipaddress172.16.30.1255.255.255.0

!

interfaceSerial1/0

bandwidth512

ipaddress172.16.5.1255.255.255.252

!

interfaceSerial2/0

ipaddress172.16.3.2255.255.255.252

!

routerospf101

network172.16.0.00.0.255.255area0

_________________________________________________________________________

hostnameCE4A

!


ipaddress172.16.40.1255.255.255.0

!

interfaceSerial1/0

bandwidth512



ipaddress172.16.5.2255.255.255.252

!

interfaceSerial2/0

ipaddress172.16.4.2255.255.255.252

!

routerospf101

network172.16.0.00.0.255.255area0

VerifyShamLinkOperation

Forroutepropagationwithoutshamlinkconfiguration,Example526showsthatwithoutshamlink172.16.40.0,172.16.20.0isreachableviaCE3A.

Example526.showiproutevrfCust_AonPE1AS1

PE1AS1#showiproutevrfCust_A


O172.16.40.0/24[110/269]via172.16.3.2,05:54:31,Serial2/0

O172.16.30.0/24[110/74]via172.16.3.2,05:54:31,Serial2/0

O172.16.20.0/24[110/397]via172.16.3.2,05:54:31,Serial2/0

O172.16.10.0/24[110/74]via172.16.1.2,05:54:31,Serial1/0

O172.16.4.0/30[110/323]via172.16.3.2,05:54:31,Serial2/0

O172.16.5.0/30[110/259]via172.16.3.2,05:54:31,Serial2/0

O172.16.2.0/30[110/387]via172.16.3.2,05:54:31,Serial2/0

Example527showsthatwithoutshamlink172.16.30.0,172.16.10.0isreachableviaCE4A.

Example527.showiproutevrfCust_AonPE2AS1

PE2AS1#showiproutevrfCust_Aospf101


O172.16.40.0/24[110/74]via172.16.4.2,05:55:48,Serial2/0

O172.16.30.0/24[110/269]via172.16.4.2,05:55:48,Serial2/0

O172.16.20.0/24[110/74]via172.16.2.2,05:55:48,Serial1/0



O172.16.10.0/24[110/397]via172.16.4.2,05:55:48,Serial2/0

O172.16.5.0/30[110/259]via172.16.4.2,05:55:48,Serial2/0

O172.16.1.0/30[110/387]via172.16.4.2,05:55:48,Serial2/0

O172.16.3.0/30[110/323]via172.16.4.2,05:55:48,Serial2/0

Example528showstheroutingtablesonCE3AandCE4Awithoutshamlink.

Example528.RoutingTablesonCE3AandCE4AWithoutShamLink



O172.16.40.0/24[110/205]via172.16.5.2,05:56:25,Serial1/0

O172.16.20.0/24[110/333]via172.16.5.2,05:56:25,Serial1/0

O172.16.10.0/24[110/138]via172.16.3.1,05:56:25,Serial2/0

O172.16.4.0/30[110/259]via172.16.5.2,05:56:25,Serial1/0

O172.16.1.0/30[110/128]via172.16.3.1,05:56:25,Serial2/0

O172.16.2.0/30[110/323]via172.16.5.2,05:56:25,Serial1/0

OE2172.16.101.1/32[110/1]via172.16.5.2,05:55:49,Serial1/0

OE2172.16.102.1/32[110/1]via172.16.3.1,05:55:50,Serial2/0

_________________________________________________________________________



O172.16.30.0/24[110/205]via172.16.5.1,05:56:40,Serial1/0

O172.16.20.0/24[110/138]via172.16.4.1,05:56:40,Serial2/0

O172.16.10.0/24[110/333]via172.16.5.1,05:56:40,Serial1/0

O172.16.1.0/30[110/323]via172.16.5.1,05:56:40,Serial1/0

O172.16.2.0/30[110/128]via172.16.4.1,05:56:40,Serial2/0

O172.16.3.0/30[110/259]via172.16.5.1,05:56:40,Serial1/0

OE2172.16.101.1/32[110/1]via172.16.4.1,05:56:05,Serial2/0

OE2172.16.102.1/32[110/1]via172.16.5.1,05:56:06,Serial1/0

Example529showsthetracerouteoutputwhenthereisnoshamlink.



Example529.TraceroutesWithoutShamLinks

CE3A#traceroute172.16.40.1

Typeescapesequencetoabort.

Tracingtherouteto172.16.40.1

1172.16.5.220msec24msec*

_________________________________________________________________________




1172.16.1.120msec24msec20msec




5172.16.2.2100msec100msec*

_________________________________________________________________________






3172.16.5.260msec60msec*

Example530showsthatwiththeOSPFcommandstoverifyshamlinks.

Example530.ShamLinks172.16.40.0and172.16.20.0AreReachableviaMPiBGPBackbone

PE1AS1#showipospfshamlinks

ShamLinkOSPF_SL0toaddress172.16.102.1isup

Area0sourceaddress172.16.101.1

Runasdemandcircuit

DoNotAgeLSAallowed.Costofusing1StatePOINT_TO_POINT,

Timerintervalsconfigured,Hello10,Dead40,Wait40,



Helloduein00:00:03

AdjacencyStateFULL(Hellosuppressed)

Index3/3,retransmissionqueuelength0,numberofretransmission0

First0x0(0)/0x0(0)Next0x0(0)/0x0(0)

Lastretransmissionscanlengthis0,maximumis0

Lastretransmissionscantimeis0msec,maximumis0msec

_________________________________________________________________________



10.10.10.2000FULL/00:00:3410.10.10.2Serial0/0

172.16.102.10FULL/172.16.102.1OSPF_SL0

172.16.30.10FULL/00:00:34172.16.3.2Serial2/0

172.16.10.10FULL/00:00:33172.16.1.2Serial1/0

Example531showsshamlinks172.16.40.0,172.16.20.0,and172.16.30.0arereachableviaMPiBGPbackbone.

Example531.ShamLinks172.16.40.0,172.16.20.0,and172.16.30.0AreReachableviaMPiBGPBackbone

PE1AS1#showiproutevrfCust_Aospf101172.16.40.0

O172.16.40.0/24[110/75]via10.10.10.102,00:19:23

_________________________________________________________________________


O172.16.20.0/24[110/75]via10.10.10.102,00:19:23

_________________________________________________________________________


O172.16.30.0/24[110/75]via10.10.10.101,00:19:58

Example532showstheroutingtableonCE3AandCE4AwhentheshamlinkisconfigureddepictingallroutesnowreachableviaMPBGPbackbone.

Example532.showiprouteospfonCE3AandCE4A





O172.16.40.0/24[110/139]via172.16.3.1,00:20:20,Serial2/0

O172.16.20.0/24[110/139]via172.16.3.1,00:20:20,Serial2/0

O172.16.10.0/24[110/138]via172.16.3.1,00:20:20,Serial2/0

O172.16.4.0/30[110/129]via172.16.3.1,00:20:20,Serial2/0

O172.16.1.0/30[110/128]via172.16.3.1,00:20:20,Serial2/0

O172.16.2.0/30[110/129]via172.16.3.1,00:20:20,Serial2/0

OE2172.16.101.1/32[110/1]via172.16.3.1,00:20:20,Serial2/0

OE2172.16.102.1/32[110/1]via172.16.3.1,00:20:20,Serial2/0

_________________________________________________________________________



O172.16.30.0/24[110/139]via172.16.4.1,00:20:39,Serial2/0

O172.16.20.0/24[110/138]via172.16.4.1,00:20:39,Serial2/0

O172.16.10.0/24[110/139]via172.16.4.1,00:20:39,Serial2/0

O172.16.1.0/30[110/129]via172.16.4.1,00:20:39,Serial2/0

O172.16.2.0/30[110/128]via172.16.4.1,00:20:39,Serial2/0

O172.16.3.0/30[110/129]via172.16.4.1,00:20:39,Serial2/0

OE2172.16.101.1/32[110/1]via172.16.4.1,00:20:39,Serial2/0

OE2172.16.102.1/32[110/1]via172.16.4.1,00:20:39,Serial2/0

OSPFPECERoutingCommandSummary

Table51showstherelevantOSPFPECEroutingcommandsusedinthischapter.

Table51.OSPFPECERoutingCommandSummary

Command Purpose

Router(configrouter)#areashamlinkcost ConfiguresashamlinkinterfaceonaPErouterinanMPLSVPNbackboneusestheareashamlinkcostcommandinrouterconfigurationmode

Router#(config)#routerospfprocessidvrfvrfname

ConfiguresthespecifiedOSPFprocessfortheVRF



Router#showipospfshamlinks DisplaysinformationaboutallshamlinksconfiguredforaPErouterintheVPNbackbone

ospf pe-ce routing protocol overview, configuration and verification

Documents