2023學年完整公開課版DataForwardingScenario

《HCNA-HNTDFastTraining》DataForwardingScenario課程團隊：葉禮兵王蘇南張悅吳偉強Foreword

TheTCP/IPprotocolsuiteoperatesasacollectionofrulesinordertosupporttheend-to-endforwardingofdata,togetherwithlowerlayerprotocolssuchasthosedefinedintheIEEE802standards.TheknowledgeofthelifecycleofdataforwardingenablesadeeperunderstandingoftheIPnetworkbehaviorforeffectiveanalysisofnetworkoperationandtroubleshootingofnetworkingfaults.TheentireencapsulationanddecapsulationprocessthereforerepresentsafundamentalpartofallTCP/IPknowledge.Page2Objectives Uponcompletionofthissection,traineeswillbeableto:Explaintheprocessstepsfordataencapsulationanddecapsulation.Troubleshootbasicdataforwardingissues.Page3ScenarioIntroductionPage4InternetHostAHostBServerAServerB10.1.1.1/2410.1.1.2/24172.16.10.1/24172.16.10.2/24RTARTBDataforwardingmaybelocalorremote,howeverthegeneralforwardingprocessisthesame.PathDiscoveryPage5Page5Network/MaskGatewayInterface0.0.0.0/010.1.1.25410.1.1.1

10.1.1.0/24- 10.1.1.1InternetHostAHostBServerAServerB10.1.1.1/2410.1.1.2/24172.16.10.1/24172.16.10.2/24RTARTB10.1.1.254/24G0/0/0HostAmusthaveknowledgeofapathtothedestination.ARPPage6HostAHostB10.1.1.1/2400-01-02-03-04-0510.1.1.2/2400-01-02-03-04-0610.1.1.254/2400-01-02-03-04-08InternetHostA>arp-aInternetaddressPhysicaladdressType10.1.1.25400-01-02-03-04-08Dynamic10.1.1.200-01-02-03-04-06DynamicRTAG0/0/0TheARPcachetableisusedtodiscoverthedatalinknexthop.AnunknownnexthopwillgenerateanARPrequest.TCPEncapsulationPage7PhysicalDataLinkNetworkTransportTCPData(IfApplicable)SegmentHostADestinationPortSequenceNumberWindowChecksumOptionsSourcePortAcknowledgementNumberHeaderLengthResv.UrgentPointerFINPSHURGSYNRSTACKPaddingECECWRNSEncapsulationisperformedoncepathisconfirmed.IPEncapsulationPage8DSFieldTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressIPOptionsVersionPacket(Datagram)HostAIPPhysicalDataLinkNetworkTransportHeaderLengthTCPData(IfApplicable)EthernetFramingPage9FrameEthernetDataFCSD.MACS.MACLengthLLCSNAPD.MACS.MACTypePhysicalDataLinkNetworkTransportIPTCPHostAFrametypeisdependantontheencapsulatedprotocols.IPistheupperlayerprotocol,sotheEthernetIIframeisused.FrameForwardingPage10HostA11010101010101010101010101…1…0100D.MAC(48bits)SFD(8bits)Preamble(56bits)Datalinklayerusescarriersensetodetectforexistingtraffic.PreambleandSFDusedtosynchronizewithforwardedframe.FrameProcessingPage11HostAHostBSFDPreambleEthernetIIFCSDataErrorCheckRTAG0/0/0DESTINATIONMAC00-01-02-03-04-08TYPE0x0800Framewillbereceivedbyallinthesamecollisiondomain.Onlythegateway(RTA)willprocesstheframe.PacketProcessingPage12DataIP10.1.1.100/24G0/0/1SFDPreambleEthernetIIFCSDataSourceIP: 10.1.1.1DestIP:172.16.10.1RTAG0/0/0Destination/MaskInterface172.16.10.0/24G0/0/1IPOptionsVerHLDSTotalLengthIdentificationFlagOffsetTTLProtocolChecksumDestinationIPischeckedagainsttheaddressofthegateway.Anewframeheaderisconstructedfollowingdiscoveryprocess.FrameDecapsulationPage13ServerAServerB172.16.10.1/2408-07-06-05-04-AA172.16.10.2/2408-07-06-05-04-BBD.MACS.MACType(0x0800)SFDPreambleEthernetIIFCSDataRTBG0/0/1FrameisforwardedwithdestinationMACaddressofServerA.ServerAcomparesinterfaceMACtoframedestinationMAC.PacketDecapsulationPage14Data(IfApplicable)IPServerAServerB172.16.10.1/2408-07-06-05-04-AA172.16.10.2/2408-07-06-05-04-BBRTBG0/0/1HeaderLengthSourceIP:10.1.1.1DestinationIP:172.16.10.1Protocol:0x06Ver.DSField.TotalLengthIdentificationFlagsFragmentOffsetTTLHeaderChecksumIPOptionsServerAcomparesownIPtodestinationaddressofIPheader.IPheaderisprocessedanddiscarded,dataisdirectedtoTCP.SegmentDecapsulationPage15TCPheaderbuildsconnectionwiththeserviceatport80.ParameterswithintheTCPheaderusedtomanageconnection.ServerBData(IfAPL)TCPServerAServerB172.16.10.1/2402-03-04-05-06-AA172.16.10.2/2402-03-04-05-06-BBDestinationPort:80SourcePort:1027SYNSequenceNumberAcknowledgementNumberURGACKPSHRSTFINHeaderLengthResv.WindowChecksumUrgentPointerOptionsPaddingECECWRNSRTBG0/0/1SummaryWhatinformationisrequiredbeforedatacanbeencapsulated?Whathappenswhenaframeisforwardedtoadestinationtowhichitisnotintended?Howdoe