TCPIP_Chapter11RoutingProtocol.

TCP/IP协议原理吴凡通信与信息工程学院网络工程系E-mail:[e-mail]:61830521(O)2020/1/10TCP/IPProtocolSuite2Chapter11RoutingProtocolsInterior(内部)andexterior(外部)routingRIPOSPFBGP-42020/1/10TCP/IPProtocolSuite3Introduction互联网由许多路由器连接起来的网络组成数据从源站点到目的站点，可能经过多个路由器一个路由器连接多个网络，当路由器收到分组，应该将分组转发到哪个网络？2020/1/10TCP/IPProtocolSuite4Introduction路由选择协议(Routingprotocol)——使得路由器能够找到到达目的地的最佳路径TosharetheknowledgeabouttheinternetTocalculatetheroutingtablebasedonthetopologyorthepolicies（策略）RoutingTableStaticroutemanuallydefineDynamicrouteroutingprotocolTable-drivenrouting（表驱动路由选择）OnerouterMoreroutedprotocolsOneroutedprotocol（例如IP）OneroutingtableOneroutedprotocolMoreroutingprotocolsConvergenceOverheadScalability2020/1/10TCP/IPProtocolSuite5Metric（度量）Metric：用来衡量通过某一网络所需的代价代价是什么？代价的度量取决于RoutingProtocolHopcount（跳数）,bandwidth（带宽）,delay（延迟）,MTU,load（负载）,reliability（可靠性）,…Routingprotocol使用Metric来选择一条bestpath（最优路）forroutingThemetricofaroute=MIN{SUM(Metricn)}Themetricofaroute＝MAX{MIN(Metricn)}64K64K10M10M10MHopcount:ABNetBandwidth:ACDNetADCBNetn∈Pathn∈Path度量取决于所需要的服务类型2020/1/10TCP/IPProtocolSuite6Convergence（收敛）ConvergenceAllroutersinanetworkagreeonthetopologyConvergencetime（收敛时间）Ameasureofhowquicklytorecoverfromnetworkchanges从不一致到一致所经历的时间体现路由算法的效率ABCDest.D2020/1/10TCP/IPProtocolSuite7Convergence（收敛）FactorsaffectingconvergenceTheroutingprotocolusedArouter’sdistancefromthepointofchangeThenumberofroutersinthenetworkBandwidthandtrafficloadoncommunicationslinksArouter’sloadTrafficpatternsinrelationtothetopologychange2020/1/10TCP/IPProtocolSuite8AutonomoussystemAutonomoussystem（自治系统，AS）AgroupofnetworksandroutersundertheauthorityofasingleadministrationEachAStypicallyrepresentsanindependentorganizationandappliesitsownuniqueroutingandsecuritypolicies域内路由和域间路由为什么需要AS？主要原因：Internet网络太大，一种路由协议无法更新所有路由器的路由表引入AS之后，路由分为intra-domainroutingIGP:InteriorGatewayProtocol（内部网关协议/域内路由）inter-domainroutingEGP:ExteriorGatewayProtocol（外部网关协议/域间路由）2020/1/10TCP/IPProtocolSuite9IGPvs.EGPIGP（intra-domain）TobeusedwithinanautonomoussystemTofindthebestpathtothenetworkIGP具有多样性，AS可自主选择Example：RIP、OSPF、IS-ISEGP（inter-domain）TobeusedbetweenautonomoussystemsTofindthebestpathtotheASAS间必须使用统一的EGPExample：BGP-4NoteThestaticroutingoranIGPcouldalsobeusedbetweenautonomoussystemsinsomecaseAS1AS2RREGPIGPIGP2020/1/10TCP/IPProtocolSuite10RoutingProtocolsRoutingprotocolsConceptoftheroutingmethodOperation:discover,topologychange,calculateFeaturesandmessagesQuestionsandsolutionsProtocolTypeRoutingmethodPopularver.RIP(路由信息协议)IGPDistancevectorroutingRIPv1,RIPv2OSPF(开放最短通路优先)IGPLinkstateroutingOSPFv2BGP(边界网关协议)EGPPathvectorroutingBGP42020/1/10TCP/IPProtocolSuite11AutonomoussystemASnumberAnidentifyingnumberthatisassignedbyanInternetregistryoraserviceprovideRange:1~65535（PrivateASnumber:64512~65535）Internet由若干AS互相连接构成每个AS内可能有多个网络存在核心主干网也可以构成一个AS核心主干网提供到所有可能的目的地的可靠的、统一的、权威的路由ASxASyAS1核心主干网AS3AS22020/1/10TCP/IPProtocolSuite12TypesofAutonomousSystemsSingle-homedAS（残桩AS）OnlyoneexitpointtotheoutsideExample:AS1,AS3数据通信量不能通过残桩ASMulti-homedASMorethanoneexitpointtotheoutsideExample:AS2NontransitAS——例如：大型公司网络notallowtransittraffictopassthroughitTransitAS（转接AS）allowtransittraffictopassthroughitAS1AS2RRRAS3R2020/1/10TCP/IPProtocolSuite13Chapter11RoutingProtocolsInteriorandexteriorroutingRIPOSPFBGP-42020/1/10TCP/IPProtocolSuite14RIPRoutingInformationProtocol，RIPv1：RFC1058，v2：RFC2453，路由信息协议IPLANsMANsWANsICMPIGMPARPRARPNetworkLayerNetworkAccessLayerTCPUDPTransportLayerRIPApplicationLayer520软件实现层次RIP=RIPv1internetGraphGraph:asetofnodesandedgesInaninternet,aroutercannormallyberepresentedbyanodeandanetworkberepresentedbyaedgesconnectingtwonodes2020/1/10TCP/IPProtocolSuite15Net2Net4internetGraph2020/1/10TCP/IPProtocolSuite16什么是DV？一个有序对（v，d）v：目的网络d：到该目的网络的距离准确说：应该是到目的网络的Metric从哪获得DV？邻居节点周期性的路由通告报文中怎么理解DV？假设路由器j从邻居i获得DV＝（v，div），表示邻居i告诉路由器j：“我可以到达某个目的网络v，我到那儿的距离是div”那么，对于路由器j就可以推出以下结论：“我通过邻居i，可以到达v，且距离是div＋dji”距离向量（DistanceVector，DV）jivdjidivDNext_hopMvidiv＋djiBellman-FordAlgorithmGiventhecostbetweeneachpairofnodes,thealgorithmcanfindtheleastcost(shortestpath)betweenanytwonodes2020/1/10TCP/IPProtocolSuite172020/1/10TCP/IPProtocolSuite18DistanceVector（距离向量）Routing基本原理：每一个路由器周期性地与其邻居路由器分享关于整个网络的路由信息“我可以通过谁到达哪些网络”“分享”WhattheentireroutingtableWhenatregularintervalsWhereonlywithneighborTocalculatetheroutingtable距离向量算法（Bellman-Ford或Ford-Fulkerson算法）通过累积distancevectors，来不断更新路由表2134561121111113465321333112244446552020/1/10TCP/IPProtocolSuite19RIPMessageFormat(=512bytes)Encapsulation:UDP(port520)采用广播的方式通告路由CommandVersionIPaddressAll0sAll0sAll0sMetric(hopcount)All0sFamilyRepeated2020/1/10TCP/IPProtocolSuite20TypesofMessagesRequest(Command=1):broadcast功能：askforaresponsecontainingallorpartoftherouter‘sroutingtable.（“问路”）AllentriesTobesentbyarouterthathasjustcomeup（当路由器刚接入网络）SpecificentriesTobesentbyarouterthathassometime-outentries（询问超时表项）Response(Command=2)Solicited（询问响应）：响应Request分组Unicasttotheas