4.6RoutingintheInternetTheGlobalInternetconsistsofAutonomousSystems(AS)interconnectedwitheachother:StubAS:smallcorporationMultihomedAS:largecorporation(notransit)TransitAS:providerTwo-levelrouting:Intra-AS:administratorisresponsibleforchoiceInter-AS:uniquestandard14:NetworkLayerInternetASHierarchyIntra-ASborder(exteriorgateway)routersInter-AS

interior(gateway)routers24:NetworkLayer4.6.1Intra-ASRoutingAlsoknownasInteriorGatewayProtocols(IGP)MostcommonIGPs:RIP:RoutingInformationProtocolOSPF:OpenShortestPathFirstIGRP:InteriorGatewayRoutingProtocol(Ciscopropr.)34:NetworkLayerRIP(RoutingInformationProtocol)DistancevectoralgorithmIncludedinBSD-UNIXDistributionin1982Distancemetric:#ofhops(max=15hops)Distancevectors:exchangedevery30secviaResponseMessage(alsocalledadvertisement)Eachadvertisement:routetoupto25destinationnets44:NetworkLayerRIP(RoutingInformationProtocol)DestinationNetwork NextRouterNum.ofhopstodest.

w A 2

y B 2

z B 7

x -- 1 …. …. ....wxyzACDBRoutingtableinD54:NetworkLayerRIP:LinkFailureandRecovery

Ifnoadvertisementheardafter180sec-->neighbor/linkdeclareddeadroutesvianeighborinvalidatednewadvertisementssenttoneighborsneighborsinturnsendoutnewadvertisements(iftableschanged)linkfailureinfoquicklypropagatestoentirenetpoisonreverseusedtopreventping-pongloops(infinitedistance=16hops)64:NetworkLayerRIPTable

processingRIProutingtablesmanagedbyapplication-levelprocesscalledroute-d(daemon)advertisementssentinUDPpackets,periodicallyrepeated74:NetworkLayerRIPTableexample(continued)Router:giroflee.eurocom.fr

ThreeattachedclassCnetworks(LANs)RouteronlyknowsroutestoattachedLANsDefaultrouterusedto“goup”Routemulticastaddress:224.0.0.0Loopbackinterface(fordebugging)

DestinationGatewayFlagsRefUseInterface-----------------------------------------------------------------127.0.0.1127.0.0.1UH026492lo0192.168.2.192.168.2.5U213fa0193.55.114.193.55.114.6U358503le0192.168.3.192.168.3.5U225qaa0224.0.0.0193.55.114.6U30le0default193.55.114.129UG014345484:NetworkLayerOSPF(OpenShortestPathFirst)“open”:publiclyavailableUsesLinkStatealgorithm

LSpacketdisseminationTopologymapateachnodeRoutecomputationusingDijkstra’salgorithmOSPFadvertisementcarriesoneentryperneighborrouterAdvertisementsdisseminatedtoentireAS(viaflooding)94:NetworkLayerOSPF“advanced”features(notinRIP)Security:allOSPFmessagesauthenticated(topreventmaliciousintrusion);TCPconnectionsusedMultiplesame-costpathsallowed(onlyonepathinRIP)Foreachlink,multiplecostmetricsfordifferentTOS(eg,satellitelinkcostset“l(fā)ow”forbesteffort;highforrealtime)Integrateduni-andmulticastsupport:MulticastOSPF(MOSPF)usessametopologydatabaseasOSPFHierarchicalOSPFinlargedomains.104:NetworkLayerHierarchicalOSPF114:NetworkLayerHierarchicalOSPFTwo-levelhierarchy:localarea,backbone.Link-stateadvertisementsonlyinareaeachnodeshasdetailedareatopology;onlyknowdirection(shortestpath)tonetsinotherareas.Areaborderrouters:

“summarize”distancestonetsinownarea,advertisetootherAreaBorderrouters.Backbonerouters:runOSPFroutinglimitedtobackbone.Boundaryrouters:connecttootherASs.124:NetworkLayerIGRP(InteriorGatewayRoutingProtocol)CISCOproprietary;successorofRIP(mid80s)DistanceVector,likeRIPseveralcostmetrics(delay,bandwidth,reliability,loadetc)usesTCPtoexchangeroutingupdatesLoop-freeroutingviaDistributedUpdatingAlg.(DUAL)basedondiffusedcomputation134:NetworkLayer4.6.2Inter-ASrouting144:NetworkLayerInternetinter-ASrouting:BGPBGP(BorderGatewayProtocol):

thedefactostandardPathVectorprotocol:similartoDistanceVectorprotocoleachBorderGatewaybroadcasttoneighbors(peers)entirepath(I.e,sequenceofASs)todestinationE.g.,GatewayXmaysenditspathtodest.Z:Path(X,Z)=X,Y1,Y2,Y3,…,Z154:NetworkLayerIn萌te您rn定et臣i輝nt宴er箱-A霸S輩ro產(chǎn)ut撇in音g:提B獄GPSu藥pp推os哨e:ga稍te摸wa欄y纖X境se扁nd察i殲ts槽p鴿at賓h辮to且p男ee啞r目ga辣te欺wa壯y夜WW形ma庭y賭or貞m度ay墻n繡ot奴s出el貢ec卵t受pa幟th丙o高ff笑er獨(dú)ed冊(cè)b床y碼Xco仇st間,黨po郵li定cy也(爸do艦n’吹t堪ro姻ut撓e疲vi歷a嬌co弊mp伍et凝it鴨or尼s慌AS紛),俘l停oo脅p糾pr堅(jiān)ev域en扔ti錢on暴r解ea貞so莫ns.If乎W仿s答el亮ec孤ts磁p鎮(zhèn)at紡h矩ad傲ve丸rt掘is潛ed遣b筆y性X,經(jīng)t任he歲n:Pa涉th勻(竄W,循Z)粗=裂w寸,任Pa棕th罰(紐奉X,本Z)No象te見:粱X漿ca眼n麗co機(jī)nt款ro碧l懲in靜co彎mi報(bào)ng降t吸ra用ff慌ic闊b載y羊co貧nt螺ro斧ll善in私g捷it傲r王ou換te汽a角dv搶er另ti鍛se號(hào)me異nt蘭s她to兵p罷ee膝rs丟:e.楊g.池,攤do篇n’敗t滔wa值nt唐t倚o竹ro誼ut雨e郊tr奴af減fi饞c炸to剪Z船-姥>訪do估n’饑t唱ad播ve偵rt稿is名e昏an在y大ro澤ut僵es箏t畫o葛Z164:們N柿et評(píng)wo容rk尸L點(diǎn)ay閣erIn北te蹦rn淹et請(qǐng)i傻nt飼er泥-A伴S私ro個(gè)ut厘in唉g:訪B具GPBG賠P戀me罩ss窮ag振es看e牧xc匹ha瘋ng胳ed頌u居si材ng浙T墊CP芬.BG稠P醋me見ss挨ag龍es綱:OP蓋EN陡:op亦en餃s懸TC場(chǎng)P凳co來nn忙ec氧ti富on性t筒o簡(jiǎn)pe廁er虧a傻nd統(tǒng)a辯ut技he犯nt思ic誼at圣es畢s寬en訊de曲rUP燥DA美TE怪:ad犁ve銜r(shí)t亂is核es恭n睜ew孫p具at婆h攝(o足r偉wi績(jī)th固dr鈴aw遠(yuǎn)s腥ol腳d)KE和EP浩AL招IV宿Eke廳ep查s霉co叢nn媽ec特ti彎on最a裳li沫ve雀i鈔n腫ab沙se呆nc奔e薯of鞭U畜PD姨AT看ES許;點(diǎn)al孟soAC貍KsOP愉EN宴r焰eq泰ue雀stNO電TI慚FI掘CA秤TI傍ON榮:re矛po鑼rt祝s勇er第ro承rs質(zhì)i藝n彎pr著ev匠io雜usms挑g;弱al曠so敗u坡se紋d速to附c維lo慎se白c蛋on這ne浩ct岔io柄n174:疤N(yùn)擁et白wo暫rk適L腰ay扮erWh隸y老di仁ff藏er卡en尼t(yī)腐In央tr腦a-赴a詢nd情I園nt至er妖-A鐮S泡ro歲ut撕in袋g胃?Po非li資cy屢:In靜te坡r-姑