AnIntroductiontoInterdomainRoutingandtheBorderGatewayProtocol(BGP)OutlineInMemoryofAbhaAhujaPARTIInternetInitiativeJapan(IIJ)IIJ,TokyoTelstrainternationalWorldCom(UUNet)UUNet,EuropeSprint,USACharlotteGARR-Bwiscnet.netMIT.eduNetworkInterconnectionsPARTIISomeCostsofRunninganISPBallparkFigures(InUS$)CustomersandProvidersThe“Peering”RelationshipPeeringProvidesShortcutsPeeringWarsRoutingvs.ForwardingHowAreForwardingTablesPopulatedtoimplementRouting?TopologyinformationisfloodedwithintheroutingdomainBestend-to-endpathsarecomputedlocallyateachrouter.Bestend-to-endpathsdeterminenext-hops.BasedonminimizingsomenotionofdistanceWorksonlyifpolicyissharedanduniformExamples:OSPF,IS-ISTheGangofFourRoutersTalkingtoRoutersAutonomousRoutingDomains(ARDs)AutonomousSystems(ASes)ASNumbers(ASNs)ASGraphsCanBeFunASGraph!=InternetTopologyAutonomousRoutingDomainsDon’tAlwaysNeedBGPoranASNASNsCanBe“Shared”(RFC2270)ABitofOGI’sASNeighborhoodABitofUOregon’sASNeighborhoodPartialViewofcs.wisc.eduNeighborhoodARD!=ASPARTIIIBGP-4BGPOperations(Simplified)TwoTypesofBGPNeighborRelationshipsiBGPMeshDoesNotScaleRoutereflectorscanpassoniBGPupdatestoclientsEachRRpassesalongONLYbestroutesORIGINATOR_IDandCLUSTER_LISTattributesareneededtoavoidloopsBGPConfederationsFourTypesofBGPMessagesBGPAttributesAttributesareUsedtoSelectBestRoutesRouteSelectionSummaryBGPRouteProcessingBGPNextHopAttributeForwardingTableImplementingCustomer/ProviderandPeer/PeerrelationshipsImportRoutesExportRoutesHowCanRoutesbeColored?BGPCommunities!CommunitiesExampleSoManyChoicesLOCALPREFERENCEPARTIVTweakTweakTweakASPATHAttributeInfairness:couldyoudothis“right”andstillscale?ExportinginternalstatewoulddramaticallyincreaseglobalinstabilityandamountofroutingstateInterdomainLoopPreventionTrafficOftenFollowsASPATH…ButItMightNotASGraphsDependonPointofViewImplementingBackupLinkswithLocalPreference(OutboundTraffic)MultihomedBackups(OutboundTraffic)SheddingInboundTrafficwithASPATHPadding.Yes,thisisaGloriousHack……ButPaddingDoesNotAlwaysW