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3IPAddressingCERTIFICATIONOBJECTIVES3.01TCP/IPProtocolStack3.02IPAddressingIntroduction3.03Subnetting3.04PlanningIPAddressing3.05FiguringOutIPAddressComponents✓Two-MinuteDrillQ&ASelfTestCertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter3BlindFolio3:1D:\omh\CertPrs8\934-9\ch03.vpMonday,August04,200310:58:47AMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreenTheTransmissionControlProtocol/InternetProtocol(TCP/IP)isastandardthatincludesmanyprotocols.Itdefineshowmachinesonaninternetworkcancommunicatewitheachother.ItwasinitiallyfundedbyanddevelopedforDARPA(DefenseAdvancedResearchProtectsAgency),whichisaconglomerationofU.S.militaryandgovernmentorganizations.Developedinitiallyforthegovernment,itwaslatermadeavailabletothepublic,mainlyseenonUnixsystems.FirstspecifiedinRFC791,ithasbecomethedefactostandardfornetworkingprotocols.TheInternetusesTCP/IPtocarrydatabetweennetworks,andmostcorporationstodayuseTCP/IPfortheirnetworks.ThischapterwillprovideanoverviewofTCP/IP,includingsomeofitsmoreimportantprotocols,aswellasIPaddressing.CERTIFICATIONOBJECTIVE3.01TCP/IPProtocolStackTohelparticulatehowdataismovedbetweendevicesrunningTCP/IP,amodelwasdevelopedthatresemblestheOSIReferenceModeldiscussedinChapter2.Table3-1comparesthetwomodels.ThefollowingsectionswillcoverthelayersoftheTCP/IPProtocolstack.ApplicationLayerOnemaindifferencebetweentheOSIReferenceModelandTCP/IP’smodelisthatTCP/IPlumpstogethertheapplication,presentationandsessionlayersintoonelayer,calledtheapplicationlayer.HerearesomecommonTCP/IPapplicationsCiscodevicessupport:DNS,HTTP,SNMP,telnet,andTFTP.2Chapter3:IPAddressingCertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter3ItisVERYimportantthatyouunderstandALLaspectsofIPaddressing.Therefore,spendalotoftimeonthischapter.Ifyoudon’tunderstandIPaddressingwhentakingtheexam,youwillhaveadifficulttimeinpassingit.ThisExamWatchgoesforallthreeexams:INTRO,ICND,andCCNA.D:\omh\CertPrs8\934-9\ch03.vpMonday,August04,200310:58:47AMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreenTransportLayerTheTCP/IPtransportlayerisresponsibleforprovidingalogicalconnectionbetweentwodevicesandcanprovidethesetwofunctions:■Flowcontrol(throughtheuseofwindowingoracknowledgements)■Reliableconnections(throughtheuseofsequencenumbersandacknowledgements)Thetransportlayerpackagesapplicationlayerdataintosegmentstosendtoadestinationdevice.Theremotedestinationisresponsiblefortakingthedatafromthesesegmentsandforwardingittothecorrectapplication.TCP/IPhastwotransportlayerprotocols:TransmissionControlProtocol(TCP)andUserDatagramProtocol(UDP).Theseprotocolsarediscussedinthefollowingsections.TCPTCP’smainresponsibilityistoprovideareliableconnection-orientedlogicalservicebetweentwodevices.Itcanalsousewindowingtoimplementflowcontrolsothatasourcedevicedoesn’toverwhelmadestinationwithtoomanysegments.TCPSegmentTCPtransmitsinformationbetweendevicesinadataunitcalledasegment.Table3-2showsthecomponentsofasegment.TCP/IPProtocolStack3CertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter3LayerOSIReferenceModelTCP/IPProtocolStackLayer7ApplicationLayer6PresentationLayer5SessionApplicationLayer4TransportTransportLayer3NetworkInternetLayer2DataLinkDataLinkLayer1PhysicalPhysicalTABLE3-1ComparisonoftheOSIReferenceModelandtheTCP/IPProtocolStackTCP/IP’stransportlayercanprovideforflowcontrolandreliableconnections.Herearesomeexamplesofapplications(andtheirports)thatuseTCP:HTTP(80),FTP(21),SMTP(25),andtelnet(23).D:\omh\CertPrs8\934-9\ch03.vpMonday,August04,200310:58:47AMColorprofile:GenericCMYKprinterprofileCompositeDefaultscreenThesegmentiscomposedofaheader,followedbytheapplicationdata.Withoutanyoptions,theTCPheaderis20-bytesinlength.TCP’sMultiplexingFunctionTCP,andUDP,provideamultiplexingfunctionforadevice:Thisallowsmultipleapplicationstosimultaneouslysendandreceivedata.Withtheseprotocols,portnumbersareusedtodifferentiatetheconnections.Portnumbersarebrokenintotwobasiccategories:well-knownportnumbers(sometimescalledreservedportnumbers)andsourceconnectionportnumbers.Eachapplicationisassignedawell-knownportnumberthatistypicallybetween1and1,023.Anytimeyouwanttomakeaconnectiontoaremoteapplication,yourapplicationprogramwillusetheappropriatewell-knownportnumber.AsyousawinTable3-2,however,therehappenstobetwoportnumbersinthesegment:sourceanddestination.Whenyouinitiateaconnectiontoaremote4Chapter3:IPAddressingCertPrs8/CCNACiscoCertifiedNetworkAssociateStudyGuide/Deal/222934-9/Chapter3TCPFieldNameLength(inbits)DefinitionSourcePort16IdentifieswhichapplicationissendinginformationDestinationPort16IdentifieswhichapplicationistoreceivetheinformationSequenceNumber32MaintainsreliabilityandsequencingAcknowledgementNumber32UsedtoacknowledgereceivedinformationHeaderLength4Numberof32-bitwordsthatcomprisetheheaderReservedField6Currentlynotused(settoallzeroes)CodeBits6Definescontrolfunctions,likesynchronizationWindowSize16IndicatesthenumberofsegmentsallowedtobesentbeforewaitingforanacknowledgmentfromthedestinationChecksum16CRC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