《计算机网络自顶向下方法与Internet特色》幻灯片.ppt

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1、Chapter4:NetworkLayer4.1Introduction4.2Virtualcircuitanddatagramnetworks4.3What’sinsidearouter4.4IP:InternetProtocolDatagramformatIPv4addressingICMPIPv64.5RoutingalgorithmsLinkstateDistanceVectorHierarchicalrouting4.6RoutingintheInternetRIPOSPFBGP4.7Broadcastandmulticastrouting1NetworkLayer因特网中的路

2、由选择全球因特网是由诸多AutonomousSystems(AS)互联而成:小型自治系统（StubAS）:中小型企业分区自治系统（MultihomedAS）:大型企业(非跨越的)跨越式自治系统（TransitAS）:NBP等两层路由选择:Intra-AS:由网管决定Inter-AS:唯一性的标准2NetworkLayer因特网的AS层次Inter-AS边界(外部网关)路由器Intra-AS内部(网关)路由器3NetworkLayerIntra-ASRoutingAS内部选路AlsoknownasInteriorGatewayProtocols(IGP)内部网关协议MostcommonIn

3、tra-ASroutingprotocols:RIP:RoutingInformationProtocolOSPF:OpenShortestPathFirstIGRP:InteriorGatewayRoutingProtocol(Ciscoproprietary)4NetworkLayerIntra-AS路由选择也称为内部网关协议InteriorGatewayProtocols(IGP)最常用的IGP有:RIP:RoutingInformationProtocol(路由选择信息协议)OSPF:OpenShortestPathFirst(开放式最短路径优先（协议）)IGRP:Interio

4、rGatewayRoutingProtocol(内部网关路由选择协议，Cisco产权)5NetworkLayerChapter4:NetworkLayer4.1Introduction4.2Virtualcircuitanddatagramnetworks4.3What’sinsidearouter4.4IP:InternetProtocolDatagramformatIPv4addressingICMPIPv64.5RoutingalgorithmsLinkstateDistanceVectorHierarchicalrouting4.6RoutingintheInternetRIPO

5、SPFBGP4.7Broadcastandmulticastrouting6NetworkLayerRIP(RoutingInformationProtocol)DistancevectoralgorithmIncludedinBSD-UNIXDistributionin1982Distancemetric:#ofhops(max=15hops)DCBAuvwxyzdestinationhopsu1v2w2x3y3z2FromrouterAtosubsets:7NetworkLayerRIPadvertisementsDistancevectors:exchangedamongneigh

6、borsevery30secviaResponseMessage(alsocalledadvertisement)Eachadvertisement:listofupto25destinationnetswithinAS8NetworkLayerRIP(RoutingInformationProtocol)距离向量算法(Distancevectoralgorithm)含在BSD-UNIX1982版中距离的度量单位:#ofhops(max=15hops)Canyouguesswhy?距离向量:通过Response报文每隔30秒交换一次(也称为广告-advertisement)每次广告:发布

7、最多为25个AS内的目的子网列表9NetworkLayerRIP:ExampleDestinationNetworkNextRouterNum.ofhopstodest.wA2yB2zB7x--1….….....wxyzACDBRoutingtableinD10NetworkLayerRIP:ExampleDestinationNetworkNextRouterNum.ofhopstodest.wA2yB2zBA75x--1….….