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1、ccie试验备考之交换增强特性（ExchangeenhancementcharacteristicsofCCIEtestpreparation）ThisarticlebyShenXunchaocontributionDOCdocumentsmayexperiencepoorbrowsingontheWAPside.ItisrecommendedthatyouselectTXTfirstordownloadthesourcefiletothelocalmachine.ExchangeCCIEtestcharacteristicso
2、fCDPCDPisenhancedforCiscodevices(routers,switches,accessserversetc.)asecondlayerprotocolisenabledbydefault,andcanfindanimportantprotocoltoidentifytheconnectedneighborswithinformationequipment.CDPrunsinallmediathatsupportSNAP(subnetworkaccessprotocol,subnetAccessProto
3、col)frametypes,includingEthernet,framerelayandATM.CDPworksonthesecondlayeroftheOSIreferencemodel,andcaninteractwithotherCiscodevices,buthasnothingtodowiththenetworklayerprotocol.ThroughallthesupportCDPinterfacetothemulticastaddress01-00-0c-cc-cc-ccsendsperiodicmessag
4、es(notification),CDPcansendmessagesusingadjacentequipment,learninformationaboutaconnecteddevice.CDPpacketformat
5、version
6、TTL
7、checksum
8、
9、TLVlist
10、datapacketseachfielddescriptionfieldlengthdescriptionversion8bitCDPVersion(Ox02version2)TTLsavetime8bitreceivershallsavethein
11、formationinthepacketlengthoftime,insecondscheckand16bitCDPdatapacketchecktheTLVlistandvariablelengthTLVTLVformatlist
12、type(16bits)
13、length(16bits)
14、
15、data(variablelength)
16、TLVtypeanddescriptiondescriptionfunctioninterfacefunctiondeviceIDidentifierdeviceaddressnetworklayer
17、addressisusuallyinterfaceaddressportIDsendingCDPpacketidentifiertosendCDPpacketsthedescriptionoftheequipment(suchasarouterorswitch)equipmentrunningsoftwareversiondescriptioninformationplatformdescribedthehardwareplatformofNativeequipmentVLAN802.1QNativeVLAN(unlabeled
18、data)applicationofVLANIDcontainsasingleormultipleapplications,eachcontainingID(VoIPphone)andthecorrespondingVLANIDtriggerwhenthedevicereceivestheCDPdatawithtriggerTLVpackage,itwillbetoreceivedatapacketsinresponse,ratherthanwaitingfortheperiodicsendingthepacketpowerin
19、terfaceconnecteddevicepowersupplylineformaximumpowerunitforMWSysNamesystemThesysObjectIDsenderMIBobjectsysObjectIDOBJECT-IDENTIFIER
