路由協議基礎內容路由協議基本介紹靜態路由協議及動態路由協議路由協議分類常用路由協議概念Internet：inter+network路由器(router):route+er路由協議:routingprotocol概念地址：10.10.10.10/24路由表：10.10.10.0/24via10.10.9.1AS：AutonomoussystemToroute,arouterneedstodothefollowing:KnowthedestinationaddressIdentifythesourcesitcanlearnfromDiscoverpossibleroutesSelectthebestrouteMaintainandverifyroutinginformationWhatIsRouting?Routersmustlearndestinationsthatarenotdirectlyconnected.WhatIsRouting?(Cont.)路由StaticDefaultDynamic（1）信息的傳播（2）路由的計算StaticRouteUsesaroutethatanetworkadministratorentersintotheroutermanuallyDynamicRouteUsesaroutethatanetworkroutingprotocoladjustsautomaticallyfortopologyortrafficchangesIdentifyingStaticandDynamicRoutesStaticRoutesConfigureunidirectionalstaticroutestoandfromastubnetworktoallowcommunicationstooccur.StaticRouteExampleThisisaunidirectionalroute.Youmusthavearouteconfiguredintheoppositedirection.DefaultRoutesThisrouteallowsthestubnetworktoreachallknown networksbeyondrouterA.路由協議種類按應用范圍分:IGP:InteriorgatewayprotocolEGP:exteriorgatewayprotocol按作用原理分:距離矢量:distancevector鏈路狀態:link-state

Anautonomoussystemisacollectionofnetworksunderacommonadministrativedomain.IGPsoperatewithinanautonomoussystem.EGPsconnectdifferentautonomoussystems.AutonomousSystems:InteriororExteriorRoutingProtocolsAdministrativeDistance:

RankingRoutes距離矢量路由協議

初始化時，所有路由器在本機形成與本地直接連接的鏈路記錄路由器向所有相連的路由器廣播路由表內已有的記錄路由器向外廣播接收到的路由信息，再在鄰路由器形成記錄相關內容路由更新：定期更新路由計算：hop或復合路由收斂：缺點：收斂慢、路由回環、路由表全部更新優化措施：毒性翻轉、水平分割、觸發更新增強型距離矢量協議典型協議RIPIGRPEIGRP鏈路狀態路由協議當路由器初始化或當網絡結構發生變化時，路由器會產生鏈路狀態廣播數據包LSA（Link-StateAdvertisement）所有路由器會通過一種被稱為刷新（Flooding）的方法來交換鏈路狀態數據。路由協議收斂以后，所有的路由器會根據其各自的鏈路狀態信息數據庫計算出各自的路由表。相關內容SPF算法層次結構Metric典型協議OSPFIS-ISAfterinitialflood,passsmallevent-triggeredlink-state

updatestoallotherroutersLink-StateRoutingProtocolsMinimizesroutingtableentriesLocalizesimpactofatopologychangewithin

anareaLink-StateNetworkHierarchyExampleLink-StateRouting

ProtocolAlgorithmsBenefitsofLink-StateRoutingFastconvergence:changesarereportedimmediatelybythesourceaffected.Robustnessagainstroutingloops:Routersknowthetopology.Link-statepacketsaresequencedandacknowledged.Bycareful(hierarchical)networkdesign,youcanutilizeresourcesoptimally.DrawbackstoLink-StateRoutingProtocolsInitialdiscoverymaycauseflooding.Memory-andprocessor-intensive.距離矢量VS鏈路狀態距離矢量路由協議：shareinformationlocallyuseadistributedroutecalculation鏈路狀態路由協議:informationdistributedunchanged;eachrouterperformalocalbest-pathcalculationBGP協議BorderGatewayProtocol廣泛應用于目前Internet上路徑矢量IBGP，EBGP路由對等體策略AutonomousSystemsAutonomousSystem65000AutonomousSystem65500IGPs:RIP,IGRP,OSPF,EIGRPEGPs:BGPAnautonomoussystem(AS)isacollectionofnetworksunderasingletechnicaladministrationIGPsoperatewithinanautonomoussystemEGPsconnectdifferentautonomoussystemsBGPIsUsedBetweenAutonomousSystemsBGPisusedbetweenautonomoussystemsGuaranteesexchangeofloop-freeroutinginformationBGPBBGPAS

65500AS

65250BGPAS

64520AS

65000ABCFEDRoutingTablePrefixes

020501 104,027BGPCharacteristicsBGPisadistancevectorprotocolwithenhancements:Reliableupdates—BGPrunsontopof

TCP(port179)Incremental,triggeredupdatesonlyPeriodickeepalivestoverifyTCPconnectivityRichmetrics(calledpathvectorsorattributes)Designedtoscaletohugeinternetworks

(forexample,theInternet)BGPinIPPacketsBGPisanadvanceddistancevectorroutingprotocolReliesonTCPforreliablesessionmanagementUsesTCPportnumber179TCPHeaderPortNo.SegmentPayloadIPHeaderProtocolNumberFrameHeaderCRCPacketPayloadFramePayload6—TCP17—UDP179—BGP23—Telnet25—SMTPTablesIGP

Routing

ProtocolBGP

Routing

ProtocolIPBGPBGPhasitsowntable,inadditiontotheIProutingtableInformationcanbeexchangedbetweenthe

twotablesAnytworoutersthathaveformedaTCPconnectioninordertoexchangeBGProutinginformationarecalledpeersorneighborsPeers=NeighborsAS65000NeighborsAS65500NeighborsACBInternalBGPWhenBGPneighborsbelongtothesameASitiscalledinternalBGP(IBGP)NeighborsdonothavetobedirectlyconnectedAIBGPNeighborsAS65000AS65500NeighborsBCExternalBGPWhenBGPneighborsbelongtodifferentautonomoussystemsitiscalledexternalBGP(EBGP)NeighborsshouldbedirectlyconnectedAAS65000AS65500EBGPNeighborsIBGPNeighborsCBPolicy-BasedRoutingBGPallowsadministratorstodefinepolicies,orrules,forhowdatawillflowthroughtheautonomoussystemsBGPAttributesBGPattributesinclude:AS-pathNext-hopLocalpreferenceMulti-exitdiscriminator(MED)OriginCommunityBGPdefinesthefollowingmessagetypes:OpenIncludesholdtimeandBGProuterIDKeepaliveUpdateInformationforonepathonly

(couldbetomultiplenetworks)IncludespathattributesandnetworksNotificationWhenerrordetectedBGPconnectionclosedaftersentBGPMessageTypesRouteSelectionDecisionProcessConsideronly(synchronized)routeswithnoASloopsandavalidnexthop,andthen:Preferhighestweight(localtorouter)Preferhighestlocalpreference(globalwithinAS)PreferrouteoriginatedbythelocalrouterPrefershortestAS-pathPreferlowestorigincode(IGP<EGP<incomplete)PreferlowestMED(fromotherAS)PreferEBGP