9Routing_Protocol.ppt

2020/6/7,ISE-UJN,1,RoutingProtocolsRIP,OSPF,BGP,ChenZhenxiangandYangbo.ISE.UniversityofJinan,AdvancedNetworkArchitectureForPostgraduates,2020/6/7,ISE-UJN,2,Section1:Background,2020/6/7,ISE-UJN,3,InternetStructure,NSFNETbackbone,Stanford,BARRNET,regional,Berkeley,PARC,NCAR,UA,UNM,Westnet,regional,UNL,KU,ISU,MidNet,regional,10ormoreYearsAgo,theInternetwas.,SingleCoreBackbone,2020/6/7,ISE-UJN,4,InternetStructure,Backboneserviceprovider,Peering,point,Peering,point,Largecorporation,Largecorporation,Small,corporation,“Consumer”,ISP,“Consumer”,ISP,“Consumer”,ISP,InternetToday,Singlecorereplacedbyanetworkofpeerbackbones=morescalable.Todaythereareover40backbones.,PeerBackbone,2020/6/7,ISE-UJN,5,HowtoarrangetheIPBlocks-Super-netting,AssignblockofcontiguousnetworknumberstonearbynetworksCalledCIDR:ClasslessInter-DomainRoutingRepresentblockswithasinglepair(first_network_address,count)Restrictblocksizestopowersof2Useabitmask(CIDRmask)toidentifyblocksize(Whichisverysimilartothesubnetmask).AllroutersmustunderstandCIDRaddressing,Example:202.194.64.0-202.194.79.0are16classCIPaddressofUJN.Wecanuse202.194.64.0/20or202.194.64.0/255.255.240.0todenoteallthe16classCIPblocks.,2020/6/7,ISE-UJN,6,Whydoweneedroutingprotocols?,2020/6/7,ISE-UJN,7,RoutePropagation,Knowasmarterrouterhostsknowlocalrouter(DefaultGateway)localroutersknowsiterouters(Maybestaticrouting)siteroutersknowcorerouters(RoutingProtocols)coreroutersknoweverything(Mayhavelargeroutetables)AutonomousSystem(AS)correspondstoanadministrativedomainexamples:University,company,backbonenetworkassigneachASa16-bitnumber(ASNumber)Two-levelroutepropagationhierarchyInteriorGatewayProtocol(eachASselectsitsown)ExteriorGatewayProtocol(Internet-widestandard),TheneedforexchangingrouteinformationleadstotheRoutingProtocol.,2020/6/7,ISE-UJN,8,PopularInteriorGatewayProtocols,RIP:RouteInformationProtocoldevelopedforXNSdistributedwithUnixdistance-vectoralgorithmbasedonhop-count,OSPF:OpenShortestPathFirstrecentInternetstandarduseslink-statealgorithmsupportsloadbalancingsupportsauthentication,Section2:,2020/6/7,ISE-UJN,9,RIP-RouteInformationProtocol,OriginallydesignedforXeroxPARCUniversalProtocol,whenitwascalledGWINFO.OneoftheroutingalgorithmsusedbytheInternet,BSD(BerkleySoftwareDistributions)beganshippingwithRIPinstalledasroutedin1982,leadingtoitswideacceptance.BasedondistancevectorroutingDidnotscalewellsufferedthecount-to-infinityproblemweaksecurityRIPisphasedoutforlargebackbonesbutstillwidelyusedforsmallernetworks,2020/6/7,ISE-UJN,10,RIP:KeyFacts,DistanceVectorprotocolusingBellman-Fordalgorithm(Anefficientalgorithmtosolvethesingle-sourceshortest-pathproblem).Hopcountistheonlymetricforpathdetermination.Maximumhopcountis15,16isunreachable.RoutingupdatesareBROADCASTevery30secondbydefault.RIPiscapableofloadbalancingovermultiplepaths.RIPsupportsbothTCP/IProutingandIPX.RIPisclassful,itdoesnotkeeptrackofsubnetmasks.,2020/6/7,ISE-UJN,11,RIP:RouteTables,Theroutetablecontainsnothingmorethanalistofdestinations,associatedmetrics,andmaintenanceinformation.,2020/6/7,ISE-UJN,12,RIP:Timers(defaults),Updateinterval:30sec.Everyhalfminute,eachrouterbroadcastsitsroutingtableinentiretytoitsneighbors.Invalidtimer:180sec.Ifnoupdateabouttherouteisreceivedinthistime,itismarkedasinvalidandadvertisedunreachable.However,itcontinuestoforwardpacketsuntilflushtimeexpires.Holddown:180sec.Whenarouterreceivesapacketdeclaringarouteunreachable,thistimerisstarted.Norouteswithworsemetricsareaccepteduntilitexpires.Flushtimer:240sec.Howlongaftertherouteisdeclareddown,beforeitiscompletelyremoved.Startsincrementingimmediatelyafterlastupdateisreceived.,2020/6/7,ISE-UJN,13,RIP:Traffic,RIPpacketsareencapsulatedinUDPpackets(max512bytes).Amaximumof25routescanbeheldinanysingleupdatepacket.,2020/6/7,ISE-UJN,14,RIP:SummaryofIssues,RIPv1constantlysendsoutupdates,necessaryornot.RIPv1sconvergencetimeisdependentuponthesetupofthetimers.BadroutescantakeMINUTEStodisappear.RIPv1hasnoVLSM(variablelengthsubnetmasks)support.Youeitherhavetouselotsofclassfulnetworks,oruseauniversalsubnetmask.RIPv1hasnoauthenticationmethod.PlugaboxintoaRIPv1networkadvertisingadestinationwithmetric0,andeveryonewilluseit.(Oratleast,trytouseit!).Max16hopslimitittobeusedinsmallnetworks.,2020/6/7,ISE-UJN,15,OSPF:OpenShortestPathFirst,OpenShortestPathFirst,aPreferredIGPinInternet.RoutingalgorithmnowusedinsidetheInternetAS.OSPFusestheLinkStateRoutingalgorithmwithmodificationstosupport:Multipledistancemetrics(geographicaldistance,delay,throughput)Supportforreal-timetrafficHierarchicalroutingSecurity,2020/6/7,ISE-UJN,16,AutonomousSystemsandAreas,OSPFdividesthenetworkintoseveralhierarchies:AutonomousSystems(ASs)groupsofsubnetsAreasGroupsofrouterswithinanASBackboneAreasGroupsofroutersthatconnectotherareastogether,Area,Area,BackboneArea,AutonomousSystem,Area,Area,Area,BackboneArea,Area,2020/6/7,ISE-UJN,17,Neighborpeersexchangereachabilityinformationneighborreachability:onerouterperiodicallytestsiftheanotherisstillreachable;exchangeHELLO/ACKmessages;usesak-out-of-nruleroutingupdates:peersperiodicallyexchangetheirroutingtables(distance-vector),2020/6/7,ISE-UJN,23,BGP-4:BorderGatewayProtocol,ASTypesstubAS:hasasingleconnectiontooneotherASCarrieslocaltrafficonlymultihomedAS:hasconnectionstomorethanoneASItcan,butrefusestocarrytransittraffictransitAS:hasconnectionstomorethanoneASCarriesbothtransitandlocaltrafficEachAShas:oneormoreborderroutersoneBGPspeakerthatadvertises:localnetworksotherreachablenetworks(transitASonly)givespathinformation,BGPistheInternet.BGPisslowerthanalloftheIGPs,butitisalsomorescalable,2020/6/7,ISE-UJN,24,BGPBasicOperations,BGPmakesroutingdecisionsbasedonnetworkpoliciesandoptimalroutesBGPupdatesarecarriedusingTCPonport179Beforeroutinginformationisexchanged,aTCP3-wayhandshakeoccursBGPmessagetypes:-OPEN:Establishapeeringsession-Update:Announcingnewroutesorwithdrawingpreviouslyannouncedroutes.-Notification:Shutsdownapeeringsession.-Keepalive:Handshakeatregularintervals.,2020/6/7,ISE-UJN,25,BGPRouteProcessing,BestRouteSelection,ApplyImportPolicies,BestRouteTable,ApplyExportPolicies,InstallforwardingEntriesforbestRoutes.,ReceiveBGPUpdates,BestRoutes,TransmitBGPUpdates,ApplyPolicy=filterroutes&tweakattributes,BasedonAttributeValues,IPForwardingTable,ApplyPolicy=filterroutes&tweakattributes,Openendedprogramming.Constrainedonlybyvendorconfigurationlanguage,BGPispolicy-based,2020/6/7,ISE-UJN,26,BGPExample,SpeakerforAS2advertisesreachabilitytoPandQnetwork128.96,192.4.153,192.4.32,and192.4.3,canbereacheddirectlyfromAS2Speakerforbackboneadvertisesnetworks128.96,192.4.153,192.4.32,and192.4.3canbereachedalongthepath(AS1,AS2).Speakercancancelpreviouslyadvertisedpaths,2020/6/7,ISE-UJN,27,MobileRouting,Howtodealwithmobilecomputers?Wantasinglenetworkaddresstoroutetoasinglecomputer,whereveritis.Example:Cellphonenumberalwayscontactsasingled