115-Distance-Vector-Rou教学讲解课件

©2002,CiscoSystems,Inc.Allrightsreserved.©2002,CiscoSystems,Inc.Al©2002,CiscoSystems,Inc.Allrightsreserved.2DistanceVectorRouting©2002,CiscoSystems,Inc.AlObjectivesUponcompletingthislesson,youwillbeableto:Describe（描述）thefeaturesoffered（提供的功能）bydistancevectorroutingprotocolsandgiveexamplesofeachDescribetheissuesassociated（引发的问题）withdistancevectorroutingandidentifysolutionstothoseissues（这些问题的解决方案）ObjectivesUponcompletingthisRouterspassperiodiccopiesofroutingtabletoneighbor

routersandaccumulatedistancevectors.DistanceVectorRoutingProtocols距离：多远矢量：哪个方向周期性地（RIP：30S）累计RouterspassperiodiccopiesoRoutersdiscoverthebestpathto

destinationsfromeachneighbor.SourcesofInformationandDiscoveringRoutes信息来源和路由获取RoutersdiscoverthebestpathSelectingthe

BestRoutewithMetrics度量值Selectingthe

BestRoutewithUpdatesproceedstep-by-step

fromroutertorouter.Maintaining维护RoutingInformation拓扑变化引起路由表更新路由器的更新进程更新路由表路由器A在下一个更新周期发出路由表更新信息路由表更新Updatesproceedstep-by-step

Eachnodemaintainsthedistancefromitselftoeachpossibledestinationnetwork.每一个节点自行维护它到每一个可能的目标网络的距离InconsistentRoutingEntries路由条目不一致距离矢量路由协议会出现路由条目不一致的情况EachnodemaintainsthedistanSlowconvergenceproducesinconsistentrouting.慢的收敛会引起路由条目的不一致InconsistentRoutingEntries(Cont.)SlowconvergenceproducesincoRouterCconcludes（推断）thatthebestpathtonetwork10.4.0.0isthroughrouterB.InconsistentRoutingEntries(Cont.)RouterCconcludes（推断）thatthRouterAupdatesitstabletoreflectthenewbuterroneous（不正确的）hopcount.InconsistentRoutingEntries(Cont.)RouterAupdatesitstabletoHopcountfornetwork10.4.0.0countstoinfinity.CounttoInfinity距离运算到无穷大Hopcountfornetwork10.4.0.0Definealimitonthenumberofhopstopreventinfiniteloops.定义一个跳数的上限防止无穷大的环路DefiningaMaximum规定一个最大的数DefinealimitonthenumberoPacketsfornetwork10.4.0.0bounce(loop)betweenroutersBandC.RoutingLoops路由环路去往10.4.0.0的数据包Packetsfornetwork10.4.0.0bItisneverusefultosendinformationaboutaroutebackinthedirectionfromwhichtheoriginalinformationcame.不向原始路由更新的方向再次发送路由更新信息SplitHorizon水平分割ItisneverusefultosendinfRoutersadvertisethedistanceofroutesthathavegonedowntoinfinity.路由器向邻居路由发送故障路由的更新信息，将其度量值标为无穷大

RoutePoisoning路由中毒RoutersadvertisethedistancePoisonreverseoverridessplithorizon.毒性反转是唯一覆盖水平分割PoisonReverse毒性反转邻居路由收到路由中毒信息后，向所有邻居发布路由中毒信息，目的是为了快速收敛PoisonreverseoverridessplitRoutePoisoning路由中毒VSPoisonReverse毒性反转路由中毒是指在路由信息在路由表中失效时，先将度量值变为无穷大，而不是马上从路由表中删掉这条路由信息。(这句话要理解，如RIP协议中，其度量值变为16，意味着路由不可达)再将其信息发布出去，这样相邻的路由器就得知这条路由己无效了……毒性反转与路由中毒,概念是不一样的，它是指收到路由中毒消息的路由器，不遵守水平分割原则将中毒消息转发给所有的相邻路由器，也包括发送中毒信息的源路由器，也就是通告相邻路由器这条路由信息己失效了……主要目的是达到快速收敛的目的。RoutePoisoning路由中毒VSPTherouterkeepsanentryforthenetwork’spossibledown

state,allowingtimeforotherrouterstorecomputeforthistopologychange.路由保持一条网络可以已经down的状态记录，并打开一个计时器，在计时器内关于此路由的更新信息被抑制。HolddownTimers抑制计时器TherouterkeepsanentryforTheroutersendsupdateswhenachangeinitsroutingtableoccurs.当路由表发生改变时，路由器马上传递路由更新而不用等待下一个更新周期TriggeredUpdates触化更新TheroutersendsupdateswhenDistanceVectorOperationDistanceVectorOperationDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConSummaryDistancevector-basedroutingalgorithms

(alsoknownasBellman-Fordalgorithms)passperiodiccopiesofaroutingtablefromroutertorouter.Whenthetopologyinadistancevectorprotocolinternetworkchanges,routingtableupdatesmustoccur.Aswiththenetworkdiscoveryprocess,topologychangeupdatesproceedstep-by-stepfromroutertorouter.Whenmaintainingtheroutinginformation,inconsistenciescanoccuriftheinternetwork’sslowconvergenceonanewconfigurationcausesincorrectroutingentries.SummaryDistancevector-basedrSummary(Cont.)Theconditioncalledcounttoinfinityariseswhenroutingtableupdatescontinuetoincreasethemetrictoadestinationthatcannotbereached,ratherthanmarkingthedestinationasunreachable.Aroutingloopoccurswhentwoormoreroutershaveincorrectroutinginformationindicatingthatavalidpathtoanunreachabledestinationexiststhroughtheotherrouters.Anumberoftechniquesareavailabletoeliminateroutingloopsincluding:splithorizon,routepoisoning,poisonreverse,holddowntimers,andtriggeredupdates.Summary(Cont.)Theconditionc115-Distance-Vector-Rou教学讲解课件©2002,CiscoSystems,Inc.Allrightsreserved.©2002,CiscoSystems,Inc.Al©2002,CiscoSystems,Inc.Allrightsreserved.31DistanceVectorRouting©2002,CiscoSystems,Inc.AlObjectivesUponcompletingthislesson,youwillbeableto:Describe（描述）thefeaturesoffered（提供的功能）bydistancevectorroutingprotocolsandgiveexamplesofeachDescribetheissuesassociated（引发的问题）withdistancevectorroutingandidentifysolutionstothoseissues（这些问题的解决方案）ObjectivesUponcompletingthisRouterspassperiodiccopiesofroutingtabletoneighbor

routersandaccumulatedistancevectors.DistanceVectorRoutingProtocols距离：多远矢量：哪个方向周期性地（RIP：30S）累计RouterspassperiodiccopiesoRoutersdiscoverthebestpathto

destinationsfromeachneighbor.SourcesofInformationandDiscoveringRoutes信息来源和路由获取RoutersdiscoverthebestpathSelectingthe

BestRoutewithMetrics度量值Selectingthe

BestRoutewithUpdatesproceedstep-by-step

fromroutertorouter.Maintaining维护RoutingInformation拓扑变化引起路由表更新路由器的更新进程更新路由表路由器A在下一个更新周期发出路由表更新信息路由表更新Updatesproceedstep-by-step

Eachnodemaintainsthedistancefromitselftoeachpossibledestinationnetwork.每一个节点自行维护它到每一个可能的目标网络的距离InconsistentRoutingEntries路由条目不一致距离矢量路由协议会出现路由条目不一致的情况EachnodemaintainsthedistanSlowconvergenceproducesinconsistentrouting.慢的收敛会引起路由条目的不一致InconsistentRoutingEntries(Cont.)SlowconvergenceproducesincoRouterCconcludes（推断）thatthebestpathtonetwork10.4.0.0isthroughrouterB.InconsistentRoutingEntries(Cont.)RouterCconcludes（推断）thatthRouterAupdatesitstabletoreflectthenewbuterroneous（不正确的）hopcount.InconsistentRoutingEntries(Cont.)RouterAupdatesitstabletoHopcountfornetwork10.4.0.0countstoinfinity.CounttoInfinity距离运算到无穷大Hopcountfornetwork10.4.0.0Definealimitonthenumberofhopstopreventinfiniteloops.定义一个跳数的上限防止无穷大的环路DefiningaMaximum规定一个最大的数DefinealimitonthenumberoPacketsfornetwork10.4.0.0bounce(loop)betweenroutersBandC.RoutingLoops路由环路去往10.4.0.0的数据包Packetsfornetwork10.4.0.0bItisneverusefultosendinformationaboutaroutebackinthedirectionfromwhichtheoriginalinformationcame.不向原始路由更新的方向再次发送路由更新信息SplitHorizon水平分割ItisneverusefultosendinfRoutersadvertisethedistanceofroutesthathavegonedowntoinfinity.路由器向邻居路由发送故障路由的更新信息，将其度量值标为无穷大

RoutePoisoning路由中毒RoutersadvertisethedistancePoisonreverseoverridessplithorizon.毒性反转是唯一覆盖水平分割PoisonReverse毒性反转邻居路由收到路由中毒信息后，向所有邻居发布路由中毒信息，目的是为了快速收敛PoisonreverseoverridessplitRoutePoisoning路由中毒VSPoisonReverse毒性反转路由中毒是指在路由信息在路由表中失效时，先将度量值变为无穷大，而不是马上从路由表中删掉这条路由信息。(这句话要理解，如RIP协议中，其度量值变为16，意味着路由不可达)再将其信息发布出去，这样相邻的路由器就得知这条路由己无效了……毒性反转与路由中毒,概念是不一样的，它是指收到路由中毒消息的路由器，不遵守水平分割原则将中毒消息转发给所有的相邻路由器，也包括发送中毒信息的源路由器，也就是通告相邻路由器这条路由信息己失效了……主要目的是达到快速收敛的目的。RoutePoisoning路由中毒VSPTherouterkeepsanentryforthenetwork’spossibledown

state,allowingtimeforotherrouterstorecomputeforthistopologychange.路由保持一条网络可以已经down的状态记录，并打开一个计时器，在计时器内关于此路由的更新信息被抑制。HolddownTimers抑制计时器TherouterkeepsanentryforTheroutersendsupdateswhenachangeinitsroutingtableoccurs.当路由表发生改变时，路由器马上传递路由更新而不用等待下一个更新周期TriggeredUpdates触化更新TheroutersendsupdateswhenDistanceVectorOperationDistanceVectorOperationDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConDistanceVectorOperation(Cont.)DistanceVectorOperation(ConSummaryDistancevector-basedroutingalgorithms

(alsoknownasBellman-Fordalgorithms)passperiodiccopiesofaroutingtablefromroutertorouter.Whenthetopologyinadistancevectorpr