华科网工18.ppt

1、HuazhongUniversityofScienceandTechnology,1,IntroductiontoComputerNetworks,Inter-domainrouting,HuazhongUniversityofScienceandTechnology,2,InternetStructure,LargeISP,LargeISP,Dial-UpISP,Stub,SmallISP,Stub,Stub,Stub,HuazhongUniversityofScienceandTechnology,3,AutonomousSystems(AS),Internetisnotasinglene

2、twork!TheInternetisacollectionofnetworks,eachcontrolledbydifferentadministrationsAnautonomoussystem(AS)isanetworkunderasingleadministrativecontrol,HuazhongUniversityofScienceandTechnology,4,ASNumbers(ASNs),ASNsare16bitvalues.,64512through65535are“private”,Genuity:1AT&T:7018,6341,5074,UUNET:701,702,2

3、84,12199,Sprint:1239,1240,6211,6242,Currentlyover11,000inuse.,HuazhongUniversityofScienceandTechnology,5,Implications,ASswanttochooseownlocalroutingalgorithmAStakescareofgettingpacketsto/fromtheirownhostsIntradomainrouting:RIP,OSPF,etcASswanttochooseownnon-localroutingpolicyInterdomainroutingmustacc

4、ommodatethisBGPisthecurrentinterdomainroutingprotocolBGP:BorderGatewayProtocol,HuazhongUniversityofScienceandTechnology,6,Example,AS-1,AS-2,AS-3,Interiorrouter,BGProuter,HuazhongUniversityofScienceandTechnology,7,Intra-Domain,AS-1,AS-2,AS-3,Interiorrouter,BGProuter,Intra-domainroutingprotocolakaInte

5、riorGatewayProtocol(IGP),e.g.OSPF,RIP,HuazhongUniversityofScienceandTechnology,8,Inter-Domain,AS-2,Interiorrouter,BGProuter,Inter-domainroutingprotocolakaExteriorGatewayProtocol(EGP),e.g.BGP,AS-1,AS-3,HuazhongUniversityofScienceandTechnology,9,Inter-DomainRouting,GlobalconnectivityisatstakeInevitabl

6、yleadstoonesingleprotocolthateveryonemustspeakUnlikemanychoicesinintra-domainroutingWhataretherequirements?ScalabilityFlexibilityinchoosingroutesIfyouweretochoose,linkstatebasedordistancevectorbased?BGPissortofahybrid:Pathvectorprotocol,HuazhongUniversityofScienceandTechnology,10,BorderGatewayProtoc

7、olPartI:E-BGP,borderrouter,internalrouter,E-BGP,AS1,AS2,TwotypesofroutersBorderrouter(Edge),Internalrouter(Core),HuazhongUniversityofScienceandTechnology,11,PurposeofE-BGP,borderrouter,internalrouter,E-BGP,A,AS1,AS2,ShareconnectivityinformationacrossASes,HuazhongUniversityofScienceandTechnology,12,P

8、artII:I-BGP,CarryingInfowithinanAS,E-BGP,A,AS2,E-BGP,HuazhongUniversityofScienceandTechnology,13,I-BGP,I-BGPneighborsdonotannounceroutesreceivedviaI-BGPtootherI-BGPneighbors.,Problem:InjectingexternalroutesintoIGP(e.g.OSPF)doesnotscaleandcausesBGPpolicyinformationtobelostI-BGPcanbeusedtodisseminateB

9、GProutestoallroutersinASBGProute+IGProutesufficetocreateforwardingtable,HuazhongUniversityofScienceandTechnology,14,JoinI-BGPwithIGPtoCreateForwardingTable,AS1,AS2,192.0.2.1,135.207.0.0/16,10.10.10.10,192.0.2.0/30,E-BGP,HuazhongUniversityofScienceandTechnology,15,MultipleRoutingProcessesonaSingleRou

10、ter,ForwardingTable,OSPFDomain,BGP,OSkernel,ForwardingTableManager,HuazhongUniversityofScienceandTechnology,16,RoutingbetweenISPs,Routingprotocol(BGP)containsreachabilityinformation(nometrics)NotaboutoptimizinganythingAllaboutpolicy(businessandpolitics)Why?MetricsoptimizeforaparticularcriteriaAT&Tsi

11、deaofagoodrouteisnotthesameasUUnetsScaleWhataBGPspeakerannouncesornotannouncestoapeerdetermineswhatroutesmaygetusedbywhom,HuazhongUniversityofScienceandTechnology,17,Nontransitvs.TransitASes,ISP1,ISP2,NontransitASmightbeacorporateorcampusnetwork.,NETA,TrafficNEVERflowsfromISP1throughNETAtoISP2(Atlea

12、stnotintentionally!),IPtraffic,InternetServiceproviders(often)havetransitnetworks,HuazhongUniversityofScienceandTechnology,18,SelectiveTransit,NETB,NETC,NETAprovidestransitbetweenNETBandNETCandbetweenNETDandNETC,NETA,NETD,NETADOESNOTprovidetransitBetweenNETDandNETB,Mosttransitnetworkstransitinaselec

13、tivemanner,HuazhongUniversityofScienceandTechnology,19,CustomersandProviders,CustomerpaysproviderforaccesstotheInternet,provider,customer,HuazhongUniversityofScienceandTechnology,20,CustomersDontAlwaysNeedBGP,provider,customer,Defaultroute0.0.0.0/0pointingtoprovider.,Configuredroute192.0.2.0/24point

14、ingtocustomer,192.0.2.0/24,StaticroutingisthemostcommonwayofconnectinganautonomousroutingdomaintotheInternet.ThishelpsexplainwhyBGPisamysterytomany,HuazhongUniversityofScienceandTechnology,21,Customer-ProviderHierarchy,IPtraffic,provider,customer,HuazhongUniversityofScienceandTechnology,22,ThePeerin

15、gRelationship,PeersprovidetransitbetweentheirrespectivecustomersPeersdonotprovidetransitbetweenpeersPeers(often)donotexchange$,trafficallowed,trafficNOTallowed,HuazhongUniversityofScienceandTechnology,23,PeeringProvidesShortcuts,Peeringalsoallowsconnectivitybetweenthecustomersof“Tier1”providers.,Hua

16、zhongUniversityofScienceandTechnology,24,BGP:PathVectorProtocol,DistancevectoralgorithmwithextrainformationForeachroute,storethecompletepath(ASs)Noextracomputation,justextrastorageAdvantages:canmakepolicychoicesbasedonsetofASsinpathcaneasilyavoidloops,HuazhongUniversityofScienceandTechnology,25,BGPO

17、perations(Simplified),EstablishsessiononTCPport179,Exchangeallactiveroutes,Exchangeincrementalupdates,AS1,AS2,WhileconnectionisALIVEexchangerouteUPDATEmessages,BGPsession,HuazhongUniversityofScienceandTechnology,26,FourTypesofBGPMessages,Open:Establishapeeringsession.KeepAlive:Handshakeatregularinte

18、rvals.Notification:Shutsdownapeeringsession.Update:Announcingnewroutesorwithdrawingpreviouslyannouncedroutes.,Announcement=prefix+attributesvalues,HuazhongUniversityofScienceandTechnology,27,AttributesareUsedtoSelectBestRoutes,192.0.2.0/24pickme!,192.0.2.0/24pickme!,192.0.2.0/24pickme!,192.0.2.0/24p

19、ickme!,Givenmultipleroutestothesameprefix,aBGPspeakermustpickatmostonebestroute(Note:itcouldrejectthemall!),HuazhongUniversityofScienceandTechnology,28,Example:MultipleASPaths,128.2/16,128.2/169701,128.2/16970181239,HuazhongUniversityofScienceandTechnology,29,ShorterDoesntAlwaysMeanShorter,AS4,AS3,A

20、S2,AS1,Path41is“better”thanpath321,HuazhongUniversityofScienceandTechnology,30,ImplementingCustomer/ProviderandPeer/Peerrelationships,WhatyouannouncedetermineswhatroutecanbeusedbywhomEnforcetransitrelationshipsOutboundroutefilteringEnforceorderofroutepreferenceproviderpeercustomer,HuazhongUniversity

21、ofScienceandTechnology,31,ImportRoutes,Frompeer,Frompeer,Fromprovider,Fromprovider,Fromcustomer,Fromcustomer,HuazhongUniversityofScienceandTechnology,32,ExportRoutes,Topeer,Topeer,Tocustomer,Tocustomer,Toprovider,Fromprovider,providerroute,customerroute,peerroute,ISProute,HuazhongUniversityofScienceandTechnology,33,HowCanRoutesbeColored?BGPCommunities!,VerypowerfulBECAUSEithasnopredefinedmeaning,CommunityAttribute=alistofcommunityvalues.(Sooneroutecanbelongtomultiplecommunities),UsedforsignalingwithinandbetweenASes,HuazhongUniversityofSciencea