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1、IntroductiontoComputerNetworksInter-domainrouting1HuazhongUniversityofScienceandTechnologyInternetStructureLargeISPLargeISPDial-UpISPStubSmallISPStubStubStub2HuazhongUniversityofScienceandTechnologyAutonomousSystems(AS)Internetisnotasinglenetwork!TheInternetisaco
2、llectionofnetworks,eachcontrolledbydifferentadministrationsAnautonomoussystem(AS)isanetworkunderasingleadministrativecontrol3HuazhongUniversityofScienceandTechnologyASNumbers(ASNs)ASNsare16bitvalues.64512through65535are“private”Genuity:1AT&T:7018,6341,5074,…UUNET
3、:701,702,284,12199,…Sprint:1239,1240,6211,6242,……Currentlyover11,000inuse.4HuazhongUniversityofScienceandTechnologyImplicationsASswanttochooseownlocalroutingalgorithmAStakescareofgettingpacketsto/fromtheirownhostsIntradomainrouting:RIP,OSPF,etcASswanttochooseownn
4、on-localroutingpolicyInterdomainroutingmustaccommodatethisBGPisthecurrentinterdomainroutingprotocolBGP:BorderGatewayProtocol5HuazhongUniversityofScienceandTechnologyExampleAS-1AS-2AS-3InteriorrouterBGProuter6HuazhongUniversityofScienceandTechnologyIntra-DomainAS-
5、1AS-2AS-3InteriorrouterBGProuterIntra-domainroutingprotocolakaInteriorGatewayProtocol(IGP),e.g.OSPF,RIP7HuazhongUniversityofScienceandTechnologyInter-DomainAS-2InteriorrouterBGProuterInter-domainroutingprotocolakaExteriorGatewayProtocol(EGP),e.g.BGPAS-1AS-38Huazh
6、ongUniversityofScienceandTechnologyInter-DomainRoutingGlobalconnectivityisatstakeInevitablyleadstoonesingleprotocolthateveryonemustspeakUnlikemanychoicesinintra-domainroutingWhataretherequirements?ScalabilityFlexibilityinchoosingroutesIfyouweretochoose,linkstateb
7、asedordistancevectorbased?BGPissortofahybrid:Pathvectorprotocol9HuazhongUniversityofScienceandTechnologyBorderGatewayProtocolPartI:E-BGPRborderrouterinternalrouterE-BGPR2R1R3AS1AS2TwotypesofroutersBorderrouter(Edge),Internalrouter(Core)10HuazhongUniversityofScien
8、ceandTechnologyPurposeofE-BGPRborderrouterinternalrouterE-BGPR2R1R3AAS1AS2youcanreach netAviametableatR1:destnexthopAR2ShareconnectivityinformationacrossASes11
