最详细的TCP_IP介绍

IntroductiontoTCP/IP,Agenda,WhatisTCP/IP?TCP/IPlayeringTransportlayerNetworklayerLinklayerGeneralintroductiontoTCP/IPSuiteIPProtocolARPICMPUDPBOOTPtheyarereservedforfutureuse.Normally,BOOTPserversattempttodeliverBOOTREPLYmessagesdirectlytoaclientusingunicastdelivery.ThedestinationaddressintheIPheaderissettotheBOOTPyourIPaddressandtheMACaddressissettotheBOOTPclienthardwareaddress.IfahostisunabletoreceiveaunicastIPdatagramuntilitknowsitsIPaddress,thenthisbroadcastbitmustbesettoindicatetotheserverthattheBOOTREPLYmustbesentasanIPandMACbroadcast.Otherwisethisbitmustbesettozero.ClientIPaddress:Setbytheclient,eithertoitsknownIPaddressor.YourIPaddress:SetbytheserveriftheclientIPaddressfieldwas.ServerIPaddress:Setbytheserver.,BOOTP&DHCP(4),RouterIPaddress:ThisistheaddressofaBOOTPrelayagent,notageneralIProutertobeusedbytheclient.ItissetbytheforwardingagentwhenBOOTPforwardingisbeingused.Clienthardwareaddress:Setbytheclientandusedbytheservertoidentifywhichregisteredclientisbooting.Serverhostname:OptionalserverhostnameterminatedbyX00.Bootfilename:Theclienteitherleavesthisnullorspecifiesagenericname,suchasrouterindicatingthetypeofbootfiletobeused.Theserverreturnsthefullyqualifiedfilenameofabootfilesuitablefortheclient.ThevalueisterminatedbyX00.,BOOTP&DHCP(5),Vendor-specificarea:Optionalvendor-specificarea.Typicallengthis64bytes.ThefirstfourbytesoftheoptionsfieldoftheDHCPmessagecontainthemagiccookie(9).Theremainderoftheoptionsfieldextendsto312bytesandconsistsoftaggedparametersthatarecalledoptions.,312bytes,Example:,Server,Client,(1),DHCPDISCOVER(0:0:0:0,clientsEthernetaddress),(2),DHCPOFFER(serverofferaIPaddress0),(3),DHCPREQUEST(clientask0),(4),DHCPACK,(5),useARPtoverify(ARPrequest:Whoisserver?),ARPreply,Agenda,WhatisTCP/IP?TCP/IPlayeringTransportlayerNetworklayerLinklayerGeneralintroductiontoTCP/IPSuiteIPProtocolARPICMPUDPBOOTP&DHCPTFTPTCP,TFTP:TrivialFileTransferProtocol,IPheader,UDPheader,opcode(1=RRQ)(2=WRQ),20byte8byte2Nbytes1Nbytes1,filename,0,mode,0,opcode(3=data),blocknumber,data,opcode(4=ACK),opcode(5=error),errornumber,0,errormessage,blocknumber,220-512bytes,22N1,22,IPdatagram,Agenda,WhatisTCP/IP?TCP/IPlayeringTransportlayerNetworklayerLinklayerGeneralintroductiontoTCP/IPSuiteIPProtocolARPICMPUDPBOOTP&DHCPTFTPTCP,TCP:TransmissionControlProtocol,TCPisaconnection-orientedprotocol,whileUDPisaconnectionless-orientedprotocol.TCPhasconjunctioncontrolwhichUDPlacks.ImportantcharacteristicsaboutTCP:StreamdatatransferDividedintooctets(bytes)ReliabilityUsingsequencenumbertoidentifyeachbyteinthestreamofdataThree-wayhandshakeFlowcontrolSlidewindowmechanismLogicalconnectionBothsidesagreetocommunicate,create“connection”,verifycommunicationanddetectfailureDatagramsmaystilltakedifferentpathsFullduplexTwostreamsflowinginoppositedirectionswithnoapparentinteractionControlinformationcanbepiggybackedonoppositeflow,TCP:TransmissionControlProtocol,16-bitsourceportnumber,16-bitsourceportnumber,32-bitsequencenumber,32-bitacknowledgmentnumber,4-bitheaderlength,16-bitwindowsize,16-bitTCPchecksum,16-biturgentpointer,Reserved(6bits),URG,ACK,PSH,RST,SYN,FIN,options(ifany),data(ifany),0,1516,31,20,Source/DestinationportSequenceNumberIdentifiesthepositioninthesendersbytestreamofthedatainthesegmentAcknowledgementNumberIdentifiesthenumberoftheoctetthatthesourceexpectstoreceivenext,TCP:TransmissionControlProtocol,16-bitsourceportnumber,16-bitsourceportnumber,32-bitsequencenumber,32-bitacknowledgmentnumber,4-bitheaderlength,16-bitwindowsize,16-bitTCPchecksum,16-biturgentpointer,Reserved(6bits),URG,ACK,PSH,RST,SYN,FIN,options(ifany),data(ifany),0,1516,31,20,Headerlengthin32-bitwordsCodeBitsURGUrgentpointerfieldisvalidACKAcknowledgementfieldisvalidPSHThissegmentrequestsapushRSTResettheconnectionSYNSynchronizesequencenumbersFINSenderhasreachedendofitsbytestream,TCP:TransmissionControlProtocol,16-bitsourceportnumber,16-bitsourceportnumber,32-bitsequencenumber,32-bitacknowledgmentnumber,4-bitheaderlength,16-bitwindowsize,16-bitTCPchecksum,16-biturgentpointer,Reserved(6bits),URG,ACK,PSH,RST,SYN,FIN,options(ifany),data(ifany),0,1516,31,20,WindowUsedinACKsegments.Itspecifiesthenumberofdatabytes,beginningwiththeoneindicatedintheacknowledgmentnumberfieldthatthereceiver(=thesenderofthissegment)iswillingtoaccept.,Server,Client,segment1(activeopen),segment2,segment3,SYNJ,Establishedconnection,ackK+1,SYNK,ackJ+1,(passiveopen),FINM,Terminatedconnection,ackN+1,FINN,ackM+1,ackM+1,deliverEOFtoapplication,TCP:Connectionestablishmentandtermination,TCP:SlideWindowmechanism(1),segment1,ACK,segment2,ACK,Idle,Idle,Notefficientenough,TCP:SlideWindowmechanism(2),segment1,ACK,ACK,segment2,segment3,segment4,segment5,TCP:SlidingWindowmechanism(3),segment1,ACK,ACK,segment2,segment3,segment4,segment5,Howslidingwindowworks?,TCP:Acknowledgment,DatastreamdividedintosegmentsSegmentsmaybelostorarriveoutoforderTargetreconstructsoctetstreamAcknowledgementspecifiesthenextoctettargetexpectstoreceive.AdvantagesEasytogenerateUnambiguousLostacknowledgmentsmaynotrequireretransmissionDisadvantagesSourcedoesnotknowaboutallsuccessfultransmissionsWhathappensiffivesegmentstransmittedbutfirstoneislost?,TCP:example,segment1,segment2,segment3,segment4,segment5,TXdatabuffer,time,ack2,ack2,t,segment1,segment2,segment3,segment2,ack4,segment1,segment2,segment3,RXdatabuffer,TCP:RetransmissionandTimeout,Whattimeoutvalueshouldbeused?Needlowvaluetoquicklydetectpacketloss.Butifvaluetoolow,unnecessaryretransmissionswastebandwidth.Ifvaluetoohigh,timewastedwaitingfortimeouttooccurTCPusesadaptiveretransmission.CanmeasureRoundTripTime(RTT)foreachsegment.Adjusttimeoutvaluebasedonmoving,weightedaverageofRTT.ActualRTTvariesdependingonnetworkload.Asload