英語版培訓(xùn)課件：Wide Area Networking Protocols

WideAreaNetworkingProtocolsOverview1.0 WideAreaNetworks2.0 High-LevelData-LinkControlProtocol(HDLC)3.0 Point-to-PointProtocol(PPP)4.0 FrameRelay5.0 IntegratedServicesDigitalNetwork6.0 Dial-onDemandRouting(DDR)1.0 WideAreaNetworks1.1 IntroductiontoWideAreaServices1.2 DefiningWANTerms1.2 WANConnectionTypes1.3 WANProtocols1.1 IntroductiontoWideAreaServicesToextendLANstootherLANsatremotesitesConnectingsitestogethersoinformationcanbeexchangedServiceprovidersleaseorsharetheiralreadyinstalledconnections1.2 DefiningWANTerms(WANServiceProviders)CustomerPremisesEquipment(CPE)Equipmentthatisownedandlocatedatthesubscriber’spremisesDemarcation(demarc)TheplacewheretheCPEendsandthelocalloopportionoftheservicebegins(usuallyinthe“phone-closet”)LocalLoopConnectsthedemarctotheclosestswitchingoffice(CO)CentralOffice(CO)/PointofPresence(POP)Connectsthecustomerstotheprovider’sswitchingnetwork.TollNetworkTheswitchesandfacilities,(trunks),insidetheWANprovider’s“cloud”.SynchronousserialAsynchronousserial,ISDNSynchronousserial1.3 WANConnectionTypesDedicatedLeasedlines(PointtoPointConnection)Apre-establishedWANcommunicationspathfromtheCPE,throughtheDCEswitch,totheCPEoftheremotesite,allowingDTEnetworkstocommunicateatanytimewithnosetupproceduresbeforetransmittingdata.CircuitSwitchingSetsuplinelikeaphonecall.Nodatacantransferbeforetheend-to-endconnectionisestablished.Usedial-upmodemsandISDN.Itisusedforlow-bandwidthdatatransfers.PacketSwitchingSharebandwidthwithothercompaniestosavemoney.Fornotconstantlydatatransmission(otherwiseusingleasedline)TelephoneCompanyServiceProviderSpeedupto45MbpsLow-bandwidthdatatransfersSpeedrangefrom56Kto2.048M1.4 WANProtocolsFrameRelayPacket-switchedtechnologywithDataLinkandPhysicalLayerspecificationProvideDynamic-bandwidthallocationandcongestioncontrolISDN(IntegratedServicesDigitalNetwork)VoiceandDatatransmissionoverexistingphonelinesHigherspeedthananalogdial-uplink;goodchoiceasabackuplinkLAPB(LinkAccessProcedure,Balanced)Aconnection-orientedprotocolattheDataLinklayerforusewithX.25Veryhighoverhead;onlyusediflinkisveryerrorproneHDLC(High-LevelDataLinkControl)DerivedfromSynchronousDataLinkControl(SDLC)createdbyIBMAconnection-orientedprotocolattheDataLinkLayer,lowoverheadEachvendor’sHDLCisproprietaryfortheirequipmentPPP(Point-to-PointProtocol)Anindustry-standardprotocol,tocreatepoint-to-pointlinksbetweendifferentvendor’sequipmentAllowauthenticationandmulti-linkconnections,runoverasyn.&syn.links2.0 High-LevelData-LinkControlProtocol(HDLC)ISOstandard,bit-orientedDataLinklayerprotocolApoint-to-pointprotocolusedonleasedlinesDefaultencapsulationusedbyCiscoroutersoversynchronousseriallinks;ortypethefollowingcommandsRouter(config-if)#EncapsulationhdlcEachvendorhasadifferentwayfortheHDLCprotocoltocommunicatewiththeNetworklayerprotocolNoauthenticationSynchronousPhysicalMediaHDLCIPIPXAppleTalkBit-orientedprotocolsusesinglebitascontrolinformation(byte-orienteduseentirebyte)3.0 Point-to-PointProtocol3.1 IntroductiontoPPP3.2 Point-to-pointProtocolStack3.3 LinkControlProtocol(LCP)ConfigurationOptions3.4 PPPSessionEstablishment3.5 PPPAuthenticationMethods3.6 ConfiguringPPPonCiscoRouters3.7 VerifyingPPPEncapsulation3.1 IntroductiontoPPPAData-link,point-to-pointprotocolusedOverasynchronousserial(dialup)Oversynchronousserial(ISDN,Leasedline)LCP(LinkControlProtocol)tobuildandmaintaindata-linkconnectionsUsetotransportlayer-3packetsacrossaData-linklayerComponents:EIT/TIA-232-C(formerlyRS-232)–physicallayerinternationalstandardforserialcommunicationHDLC–AmethodforencapsulatingdatagramsoverseriallinksLCP–Amethodofestablishing,configuring,maintaining,andterminatingthepoint-to-pointconnectionNCP–EncapsulatingdifferentNetworklayerprotocolacrossaPPPdatalink3.2 Point-to-pointProtocolStackNetworkLayerIPIPXOthers,e.g.AppleTalkIPCPIPXCPOthers…DataLinkLayerNetworkControlProtocol(NCP)LinkControlProtocol(LCP)Authentication,otheroptionsHigh-LevelDataLinkControlProtocol(HDLC)PhysicalLayerSynchronousorAsynchronousPhysicalMedia(suchasEIA/TIA-232,V.24,V.35,ISDN)PPPServiceProviderTCP/IPAppleTalkPPPEncapsulationTCP/IPIPXAppleTalkIPX3.3 LinkControlProtocol(LCP)ConfigurationOptions LCPoffersPPPthefollowingoptions:AuthenticationPAP&CHAPCompressiontoincreasethethroughputofPPPconnection(Stacker&Predictor)ErrorDetectionQuality&MagicNumberMulti-linkstartinginIOS11.1SplitstheloadforPPPovertwoormoreparallelcircuits(bundle)3.4 PPPSessionEstablishmentThreephasesofsessionestablishmentLink-establishmentphaseLCPpacketsaresentbyeachPPdevicetoconfigureandtestthelinkAuthenticationphase(optional)CHAPorPAPisusedtoauthenticatealinkNetwork-layerprotocolphaseNCPtoencapsulatemultipleNetwork-layerprotocolsandthensendoveraPPPdatalink3.5 PPPAuthenticationMethodsPasswordAuthenticationProtocol(PAP)LesssecurePasswordsaresentincleartextOnlyperformupontheinitiallinkestablishmentWhenthePPPlinkisfirstestablished,theremotenodesentbacktheusernameandpasswordforauthenticationatthesendingrouterChallengeAuthenticationProtocol(CHAP)UsedattheinitialstartupofalinkandatperiodiccheckupachallengerequestAvaluecalculatedwithMD5Checkthevalue,ifnotmatch->terminateatonce!*MD5isaone-wayhashfunction3.6 ConfiguringPPPonCiscoRoutersRouter(config-if)#EncapsulationpppConfiguringPPPencapsulationonaninterface(serial)Router(config)#Hostname<hostnameoflocalrouter>Username<hostnameofremoterouter>password<password>Case-sensitiveandPlain-textpasswordThepasswordonbothroutersmustbethesameBoththelocalandremoteroutermustbeconfiguredRouter(config-if)#pppauthenticaiton{chap|pap}Configuringtheauthenticationtypeonaninterface(serial)Ifbotharechosen,thefirstonewillbeused.Ifthefirstonefailed,thesecondonewillbeused.3.7 VerifyingPPPEncapsulationRouter#Showints0Showtheencapsulationmethod,protocolsupport,etc.Router#DebugpppauthenticationVerifythePPPauthenticationconfiguration4.0 FrameRelay4.1 IntroductiontoFrameRelay4.2 FrameRelayTerminology4.3 DataLinkConnectionIdentifiers(DLCIs)4.4 LocalManagementInterface(LMI)4.5 Sub-interface4.6 MappingFrameRelay4.7 FrameRelayConfigurationTasks4.8 FrameRelayCongestionControl4.9 CommittedInformationRate(CIR)4.10 MonitoringFrameRelay4.1 IntroductiontoFrameRelayFrameRelayworksonphysicalanddatalinklayer.FrameRelayprovidesconnection-oriented,DataLinklayercommunicationviavirtualcircuitsjustasX.25does.ThesevirtualcircuitsarelogicalconnectionscreatedbetweentwoDTEsacrossapacket-switchednetwork,whichisidentifiedbyaDLCI,orDataLinkConnectionIdentifier.FrameRelayismoreefficientandfasterthanX.25becauseitassumeserrorcheckingwillbedonethroughhigher-layerprotocolsandapplicationservices.Also,likeX.25,FrameRelayusesbothPVCs(PermanentVirtualCircuits)andSVCs(SwitchedVirtualCircuits),althoughmostFrameRelaynetworksuseonlyPVCs.Thisvirtualcircuitprovidesthecompletepathtothedestinationnetworkpriortothesendingofthefirstframe.FrameRelayisusedoveravarietyofnetworkprotocols.FrameRelayinterfacebetweentheuserandthenetworkequipmentwilltransmitandreceiveframesusingfirst-infirst-outqueuingonastatisticallymultiplexedcircuit4.2 FrameRelayTerminologyHub/SwitchDSU/CSURouterDLCI16

DSU/CSUUserDemarcCentralOfficeDemarcDSU/CSUHub/SwitchRouterDLCI17

DSU/CSUUserFrameactuallytransversethisPVCRouterseethisUseronlyseethisFrameRelaynetworkallowuserstocommunicatebetweentwoDTEdevicesthroughDCEdevices.123456Rememberthatbeforedataissentthroughthecloud,thevirtualcircuitiscreatedfromendtoend.CentralOfficeWAN784.3 DataLinkConnectionIdentifier(DLCI)AssignmentFrameRelayvirtualcircuits(PVCs)areidentifiedbyDLCIs.FrameRelayprovidersetsuptheDLCInumberstobeusedbytheroutersforestablishingPVCsFortheIPdevicesateachendofavirtualcircuittocommunicate,theirIPaddressesneedtobemappedtoDLCIs.Thismappingcanfunctionasamultipointdevice—onethatcanidentifytotheFrameRelaynetworktheappropriatedestinationvirtualcircuitforeachpacketthatissentoverthesinglephysicalinterface.ThemappingscanbedonedynamicallythroughIARPormanuallythroughtheFrameRelaymapcommand.EachDLCIislocallysignificant.ThatmeansDLCInumbersdonotnecessarilyneedtobeunique.TwoDLCInumberscanbethesameondifferentsidesofalinkbecauseFrameRelaymapsalocalDLCInumbertoavirtualcircuitoneachinterfaceoftheswitch.EachremoteofficecanhaveitsownDLCInumberandcommunicatewiththecorporateofficeusinguniqueDLCInumbers.DLCIstartat16.DLCI1023isspecificforLMIuse,DLCIs1019to1022addressmulticastMapentryindicatesstaticroutetodestination4.4 LocalManagementInterface(LMI)TheLMIisasignalingstandardbetweenaCPEdevice(router)andaframeswitch.TheLMIisresponsibleformanagingandmaintainingstatusbetweenthesedevices.LMImessagesprovideinformationaboutthefollowing:KeepalivesVerifydataisflowingMulticastingProvidesalocalDLCIPVCMulticast

addressingProvidesglobalsignificanceStatusofvirtualcircuitsProvidesDLCIstatusTherearethreestandardLMIsignalingformatsaresupported:CiscoLMIdefinedbytheGangofFour(default)ANSIAnnexDdefinedbyANSIstandardT1.617ITU-T(q933a)AnnexAdefinedbyQ.933RoutersreceiveLMIinformationonaframe-encapsulatedinterfaceandupdatethevirtualcircuitstatustooneofthreedifferentstates:ActivestateEverythingisupandrouterscanexchangeinformation.InactivestateTherouter’sinterfaceisupandworkingwithaconnectiontotheswitchingoffice,buttheremoterouterisnotworking.DeletedstateThismeansthatnoLMIinformationisbeingreceivedontheinterfacefromtheswitch.Itcouldbeamappingproblemoralinefailure.4.5 SubinterfacesCreatingSubinterfacesinordertohavemultiplevirtualcircuitsonasingleserialinterfaceandyettreateachasaseparateinterface(withdifferentconfiguration).Defineslogicalsub-interfacesontheseriallineEachsub-interfaceusesaDLCItorepresentsthedestinationsforFrameRelayPVCnetworkEachsub-interfaceusesitsownsub-networkWorkforPartialmeshFrameRelaynetworkConfiguringsubinterfacesactuallyworkstosubdividetheFrameRelaynetworkintosmallersubnetworks.Subinterfacesalsosolvetheproblemwithroutingprotocolsthatusesplithorizon.Therearetwotypesofsubinterfaces:Point-to-pointUsedwhenasinglevirtualcircuitconnectsoneroutertoanother.Eachpoint-to-pointsubinterfacerequiresitsownsubnet.MultipointUsedwhentherouteristhecenterofastarofvirtualcircuits.Usesasinglesubnetforallrouters’serialinterfacesconnectedtotheframeswitch.4.6 MappingFrameRelayInorderforIPdevicesattheendsofvirtualcircuitstocommunicate,theiraddressesmustbemappedtotheDLCIs.Therearetwowaystomakethismappinghappen:UsetheFrameRelaymapcommandformanuallymapping.ThisisalsotheonlywaytoconfiguremultipleframeencapsulationtypesonaninterfaceUsetheinverse-arp(bydefaultenable)functiontoperformdynamicmappingoftheIPaddresstotheDLCInumberbutit’snotasstableasusingthemapcommand-becausevirtualcircuitscanbeinsidiouslyanddynamicallymappedtounknowndevices.4.7 FrameRelayConfigurationTasks(1)Router(config-if#encapsulationframe-relay[cisco|ietf]Setsframerelayencapsulationforconnectiontonon-CiscoRouters(thedefaultencapsulationisforsameCiscoRouters)Router(config-if)#frame-relaylmi-type[ansi|cisco|q933a]SelectsLMItypeBeginningwithIOSversion11.2,theLMItypeisauto-sensed.ThisenablestheinterfacetodeterminetheLMItypesupportedbytheswitch.Router(config-if)#frame-relaymap<protocol>protocol-address<DLCI>[cisco|ietf][broadcast]DefineshowtoreachadestinationThebroadcastkeywordattheendtellstheroutertoforwardbroadcastsforthisinterfacetothisspecificvirtualcircuit.RememberthatFrameRelayisanonbroadcastmultiaccess(NBMA)encapsulationmethod,whichwillnotbroadcastroutingprotocolsbydefault.4.7 FrameRelayConfigurationTasks(2)Router(config)#interface<type>.sub-interface-number{point-to-point|multipoint}Createsthelogicalsub-interfaceforFrameRelayGenerallythesubinterfacenumbermatchestheDLCInumberbutthisisnotarequirement–itonlyhelpsintheadministrationoftheinterfaces.Router(config-if)#frame-relayinterface-dlci<dlci>AssignsaDLCItotheFrameRelaysub-interfaceontherouter4.8 FrameRelayCongestionControlFrameRelayswitchcontrolcongestionasfollows:DE(DiscardEligibility)WhenaFrameRelayrouterdetectscongestionontheFrameRelaynetwork,itwillturntheDEbitoninaFrameRelaypacketheader.Iftheswitchiscongested,theFrameRelayswitchwilldiscardthepacketswiththeDEbitsetfirst.IfyourbandwidthisconfiguredwithaCIRofzero,theDEwillalwaysbeon.FECN(Forward-ExplicitCongestionNotification)WhentheFrameRelaynetworkrecognizescongestioninthecloud,theswitchwillsettheFECNbitto1inaFrameRelaypacketheader.ThiswillindicatetothedestinationDCEthatthepathjusttraversediscongested.BECN(Backward-ExplicitCongestionNotification)WhentheswitchdetectscongestionintheFrameRelaynetwork,itwillsettheBECNbitinaFrameRelaypacketandsendittothesourcerouter,tellingittoslowdowntherateatwhichitistransmittingpackets.4.9 CommittedInformationControl(CIR)FrameRelayisbasedontheassumptionthatnotallcustomersneedtotransmitconstantdataallatthesametime.FrameRelayworksbestwithburstytraffic.FrameRelayprovidersallowcustomerstobuyaloweramountofbandwidththanwhattheyreallymightneed.ThisiscalledtheCommittedInformationRate(CIR).TheCIRspecifiesthataslongasthedatainputbyadevicetotheFrameRelaynetworkisbeloworequaltotheCIR,thenthenetworkwillcontinuetoforwarddataforthePVC.However,ifdataratesexceedtheCIR,itisnotguaranteed.YoucanuseazeroCIRtosavemoneyifretransmissionofpacketsisacceptable.However,understandthattheDEbitwillalwaysbeturnedonineveryframe.4.10 MonitoringFrameRelayshowframe-relaylmicommandwillgiveyoutheLMItrafficstatisticsexchangedbetweenthelocalrouterandtheFrameRelayswitch.showframepvccommandwilllistallconfiguredPVCsandDLCInumbers.thestatusofeachPVCconnectionandtrafficstatisticsthenumberofBECNandFECNpacketsreceivedontheroutershowinterfacecommanddisplaysline,protocol,DLCI,andLMIinformationshowframemapcommandwillshowyoutheNetworklayer–to–DLCImappingsdebugframelmicommandwillshowoutputontherouterconsolesbydefault.TheinformationfromthiscommandwillallowyoutoverifyandtroubleshoottheFrameRelayconnectionbyhelpingyoutodeterminewhethertherouterandswitchareexchangingthecorrectLMIinformation5.0 IntegratedServicesDigitalNetwork(ISDN)5.1 IntroductiontoISDN5.2 ISDNComponents5.3 BasicRateInterface(BRI)5.4 PrimaryRateInterface(PRI)5.5 ISDNwithCiscoRouters5.6 ISDNConfigurationTasks5.7 ISDNConfigurationExample5.1 IntroductiontoISDNAsetofcommunicationprotocolsproposedbytelephonecompanyallowingdigitalservicesrunoverexistingtelephonenetworksSupportdata,text,voice,music,graphicandvideotransmissionsimultaneously,e.g.High-speedimageapplicationsHigh-speedfiletransferVideo-conferencingMultiplelinksintohomesoftelecommutersReferencedbyasuiteofITU-TstandardsthatencompasstheOSImodel’sphysical,DataLinkandNetworklayersPPPistypicallyusedwithISDNtoprovidedataencapsulation,linkintegrityandauthentication.Benefits:Cancarryvoice,video,anddatasimultaneouslyHasfastercallsetupthanamodemHasfasterdataratesthanamodemconnectionTwoTransferInterfaces:BasicRateInterfaceandPrimaryRateInterface5.2 ISDNComponents(1)ISDNTerminalEquipmentTypes:NT1–(NetworkTermination1)ConvertBRIsignalsintoaformusedbytheISDNdigitallineNT2–switchorISDNPBX(typicallyaprovider’sequipment)TE1–(TerminalEquipment1)understandISDNstandardsTE2–Non-ISDNdevice,predateISDNstandards,requireaTATA–(TerminalAdapter),e.g.ISDNmodemwhichconvertV.35,andothersignalsintoBRIsignalsReferencePointsdescribetheinterfacebetween:R–non-ISDNandTAS–userterminalsandNT2T–NT1andNT2devicesU–NT1andlineterminationTANT1US/TRTE2NT1US/TTE1Routerwithbuilt-inNT1ISDNSwitchserviceUReferencepointsareaseriesofspecificationdefiningtheconnectionbetweenthevariousequipmentusedinanISDNnetworkL1L1-L3L4–L7L4–L75.2 ISDNComponents(2)ISDNProtocolsseries(definedbytheITU)ISDNSwitchTypesTheswitchtypesandthecorrespondingkeywordusedwiththeisdnswitch-typecommandtoconfiguretherouterconnectedtoSwitchTypeKeywordAT&TbasicrateswitchBasic-5essNortelDMS-100basicrateswitchBasic-dms100NationalISDN-1SwitchBasic-nilAT&T4ESS(ISDNPRIonly)Primary-4essAT&T5ESS(ISDNPRIonly)Primary-5essNortelDMS-100(ISDNPRIonly)Primary-dms100IssueProtocolsKeyExamplesTelephonenetworkandISDNE-seriesE.163—InternationaltelephonenumberingplanE.164—InternationalISDNaddressingConcepts,aspects,andinterfacesI-seriesI.100series—Concepts,structures,terminologyI.400series—UserNetworkInterfaces(UNIs)SwitchingandsignalingQ-seriesQ.921—LAPD(LinkAccessProcedureontheD-channel)Q.931—ISDNnetworklayerbetweenterminalandswitch5.3 BasicRateInterface(BRI)-1ISDNBRIserviceprovides:2Bchannelsoperateat64Kbps,carrydataEachchannelshouldhaveaSPID(ServiceProfileIdentifier)1Dchanneloperatesat16Kbps,carrycontrolandsignalinginformationtosetupandcontrolcallsWorkwithLAPDatheDataLinklayer;protocolsspanacrossOSI’sPhysical,DataLinkandNetworklayersAlsousedforotherfunctions(e.g.alarmsystemforabuilding)whichdoesn’tneedmuchbandwidth5.3 BasicRateInterface(BRI)-2SetupprocedureforaBRIcall:DchannelbetweenrouterandISDNswitchcomesupISDNswitchusestheSS7signalingtechniquetosetupapathtoaremoteswitchTheremoteswitchsetsuptheD-channellinktotheremoterouterTheBchannelsoflocalandremoteroutersarethenconnectedend-to-endRouterwithbuilt-inNT1ISDNSwitchserviceUNT2-ISDN

SwitchatProviderNT2-ISDN

SwitchatProviderRouterwithbuilt-inNT1LOCALREMOTEU5.4 PrimaryRateInterface(PRI)ProvidehighertransferrateMainlyuseinBusinessorPBX(PrivateBranchExchange)InNorthAmericaandJapanISDNPRIprovides23B(64K)+1D(64K)serviceTotalbitrateupto1.544MbpsInEurope,AustraliaISDNPRIprovides30B(64K)+1D(64K)serviceTotalbitrateupto2.048Mbps5.5 ISDNwithCiscoRoutersRoutershouldhavebuilt-inNT1oranISDNmodemforISDNAccessWhenconfiguringISDNyou’llneedtoknowthetypeofswitchwhatyourserviceproviderisusing(differentmanufacturerhasaproprietaryprotocolforsignaling)Needtoseewhichswitchestherouterwillsupportbyusingcommandisdnswitch-type?NT1US/TTE2Routerwithbuilt-inNT1(ISDNUport)ISDNSwitchserviceUNT2-ISDNSwitchatProviderNT1UTA(ISDNModem)TE1RouterwithISDNS/Tport5.6 ISDNConfigurationTasksRouter(config)#isdnswitch-type<switch-type> OR Router(config-if)#isdnswitch-type<switch-type>Router(config)#interfacebri<interface-number>SelectstheinterfaceforISDNBRIoperationRouter(config-if)#encapsulation[ppp|hdlc]SelectsframingforISDNBRIRouter(config-if)#isdnspid1spid-number[ldn]SetsaBchannelServiceProfileIdentifier(SPID)requiresbymanyserviceprovidersRouter(config-if)#isdnspid2spid-number[ldn]SetsaSPIDforthesecondBchannelSpid-numberisprovidedbytheISDNprovidertoidentifyyouontheswitchLdn=localdialnumber5.7 ISDNConfigurationExampleExample RouterA(config)#isdnwitch-typebasic-nel RouterA(config)#intbri0 RouterA(config-if)#encapppp(optional) RouterA(config-if)#isdnspid10865066101008650661 RouterA(config-if)#isdnspid20865066201008650662Theisdnswitch-typecommandcanbeconfiguredeitherin:Globalconfigurationmode–settheswitchtypeforallBRIintherouterInterfaceconfigurationmode–settheswitchtypeforindividualinterface6.0 Dial-on-DemandRouting(DDR)6.1 IntroductiontoDDR6.2 ConfiguringDDR6.2a ConfiguringStaticRoutes6.2b SpecifyingInterestTraffic6.2c ConfiguringtheDialerInformation6.3 OptionalCommands6.4 VerifyingtheISDNOperationRouter1CorporateIntranetRemoteNetworkModemPSTN,ISDN,InternetModemRouter16.1 IntroductiontoDDRDial-on-demandrouting(DDR)isusedtoallowtwoormoreCiscorouterstodialanISDNdial-upconnectiononanas-neededbasis.DDRisonlyusedforlow-volume,periodicnetworkconnectionsusingeitheraPublicSwitchedTelephoneNetwork(PSTN)orISDN.ThiswasdesignedtoreduceWANcostsifyouhavetopayonaper-minuteorper-packetbasis.DDRworkswhenapacketreceivedonaninterfacemeetstherequirementsofanaccesslistdefinedbyanadministrator,whichdefinesinterestingtraffic.ThefollowingfivestepsgiveabasicdescriptionofhowDDRworkswhenaninterestingpacketisreceivedinarouterinterface:Routetothedestinationnetworkisdetermined.InterestingpacketsdictateaDDRcall.Dialerinformationislookedup.Trafficistransmitted.Callisterminatedwhennomoretrafficisbeingtransmittedoveralinkandtheidle-timeoutperiodends.6.2 DDRConfigurationTasksToconfigurelegacyDDR,youneedtoperformthreetasks:1. Definestaticroutes,whichdefinehowtogettotheremotenetworksandwhatinterfacetousetogetthere.2. Specifythetrafficthatisconsideredinterestingtotherouter.3. Configurethedialerinformationthatwillbeusedtodialtheinterfacetogettotheremotenetwork.CommandsdefininginterestingtrafficDialerGroupS0orBRI0CommandssetDDRcallparametersCommandsdirectcallandtraffictogroupinterfaceDDRinterface6.2a ConfiguringStaticRoutesToforwardtrafficacrosstheISDNlink,youconfigurestaticroutes(notdynamic)ineachoftherouters.KeepthefollowinginmindwhencreatingstaticroutesDDR:Allparticipatingroutersmusthavestaticroutesdefiningallroutesofknownnetworks.Defaultroutingcanbeusedifthenetworkisastubnetwork.AnexampleofstaticroutingwithISDNisshownbelow:RouterA(config)#iproute172.16.50.0255.255.255.0172.16.60.2RouterA(config)#iproute172.16.60.2255.255.255.255bri0Thefirstlinetellstherouterhowtogettonetwork172.16.50.0,whichisthrough172.16.60.2.Thesecondlinetellstherouterhowtogetto172.16.60.2.6.2b SpecifyingInterestingTrafficSpecifyinginterestingtrafficmeanstoconfiguretheroutertodeterminewhatbringsuptheISDNline.Anadministratorusingthedialer-listglobalconfigurationcommanddefinesinterestingpackets.Router(config)#dialer-list<dialer-group>protocol<protocol-name>{permit|deny|list<access-list-number>|<access-group>}Todefineadial-on-demandrouting(DDR)dialerlistfordialingbyProtocolAcombinationofaprotocolandapreviouslydefinedaccesslistUsethedialer-groupcommandtoassociateinterfacewiththedialerlistExampleshowingthecommandstoturnonallIPtraffic:Router(config)#dialer-list1protocolippermitRouter(config)#intbri0Router(config-if)#dialer-group16.2c ConfiguringtheDialerInformationTherearefivestepsintheconfigurationofthedialerinformation.1. Choosetheinterface.2. SettheIPaddress.3. Configuretheencapsulationtype.4. Linkinterestingtraffictotheinterface.5. Configurethenumbertodialbyusingthe