计算机网络6

杭州电子科技大学《计算机与网络实验》课程实验报告实验六:DNS,DataEncapsulationandFrameExamination学院通信工程班级14083415学号14081515姓名何必锋指导教师冯维LearningObjectivesAtcompletionofthislab,youwillbeableto:1.UseWiresharktocaptureandanalyzeDNSmessage2.UnderstandhowDNSworks3.usenslookupandipconfigcommands4.ExplaintheheaderfieldsinanEthernetIIframe.5.understanddataencapsulation6.ReportandFeedbackonthislabAnswerallquestionswithsupportingscreenshots.Pleasefillinthefollowingfeedbackformandappendittothereport.Yourfeedbackisvaluabletoussothatwecanimprovethislab,andmakethecoursewelcome.BackgroundWhenupperlayerprotocolscommunicatewitheachother,dataatthesendinghostflowsdowntheTCP/IPprotocollayersandisencapsulatedintoaprotocoldataunitatlowerlayer,andfinallyencapsulatedinaLayer2frame.Forexample,DNSmessageisoftentransportedbyUDPprotocolonlayer4.SoDNSmessageatthesendinghostisencapsulatedinaUDPsegment;theUDPsegmentisthenencapsulatedinanIPpacket,andtheIPpacketisencapsulatedfinallyinalayer2frame.Theframecompositionisdependentonthemediaaccesstype,orthenetwork.Forexample,ifthemediaaccessisEthernet,thentheLayer2frameencapsulationwillbeEthernetII.Whenlearningaboutdataencapsulationandprotocoloperations,itishelpfultoanalyzetheheaderinformationfoundintheprotocoldataunits.TheDNSprotocoloperation,ipconfigcommand,andEthernetIIframeheaderwillbeexaminedinthislab.EthernetIIframescansupportvariousupperlayerprotocols.TasksTask0ProtocolLayersandDataEncapsulationAswehavediscussedinLecture02,Internetisinter-connectednetworksbasedonTCP/IPprotocols.Readtheslidesortextbooktolearnhowdatagoesthroughprotocollayersandhowdataisencapsulatedintheprotocoldataunits.Thereareconventionalnamesfortheprotocoldataunitsfordifferentlayerprotocols.Question1.Whatarenamesfortheprotocoldataunits(PDUs)forlayer4,layer3,andlayer2protocolsinTCP/IPreferencemodelbyfillingthefollowform:对协议数据单元（PDU）的名字都是什么4层、3层和2层协议，TCP/IP参考模型填充下列表格：nameforPDUoflayer4protocols:segmentnameforPDUoflayer3protocol:packetnameforPDUoflayer2protocol:frameTask1DNSandnslookupAswediscussed,IPaddressisusedtoidentifyahostuniquelyontheInternet.ButIPaddressisnotuser-friendlyandthatiswhydomainnamewasintroduced.TheDomainNameSystem(DNS)translateshostnamestoIPaddresses,providingacriticalroleintheInternetinfrastructure.Inthistask,wepracticethenslookuptool,whichisavailablebothinLinux/UnixandMSWindows.TorunnslookupinMSWindows,youneedtoopenthecommandlinewindowbystartingthecommandcmd.exe.Withnslookup,youcanqueryanyspecifiedDNSserver(bydefault,yourlocalconfiguredDNSserver)foraDNSrecord.Toaccomplishthistask,nslookupsendsaDNSquerytothespecifiedDNSserver,receivesaDNSreplyfromthatsameDNSserver,anddisplaystheresult.Typethecommandnslookup:Question2:WhatistheDNSserverIPaddressthatisusedtoqueryandfindIPaddressfor:Whataredomainnameserversforhdu.edu.cnandtheirIPaddresses?Question4:WhichDNSserverisusedtoqueryandfornameresolution?YoucanalsousenslookuptofindthemappingfromIPaddressestothehostnames.Typethecommands“nslookup192.168.156.101”and“nslookupcourse.comm.hdu.edu.cn”,andcapturetheoutput,asIdidandshowedbelowQuestion5:Canahosthavemultiplehostnames?WhatistheIPaddressformoodle.tec.hkr.se?HowmanynamesdoyoufindforthisIPaddress?可以有，IP:194.47.35.25有且只有moodle.tec.hkr.seTask2DNSandipconfigipconfig(forWindows)andifconfig(forLinux/Unix,interfaceconfiguration)areamongthemostusefultoolsfordebuggingnetworkissues.ipconfigcanbeusedtoshowyourcurrentTCP/IPinformation,includingyouraddress,DNSserveraddresses,adapter(networkinterfacecard)typeandsoon.Forexample,ifyouwanttofindallthisinformationaboutyourhost,simplyenterthecommand“ipconfig/all”inthecommandline.Question6:WhatistheIPaddressforyourcomputer,andwhatisthelocalDNSserverIPaddress?ipconfigisalsoveryusefulformanagingtheDNSinformationstoredinyourhost.Toimprovethenetworkingperformance,ahostcancacheDNSrecordsitrecentlyobtained.Toviewthesecachedrecords,youcanusethecommand“ipconfig/displaydns”.EachentryshowstheremainingTimetoLive(TTL)inseconds.Toclearthecache,enterthecommand“ipconfig/flushdns”.FlushingtheDNScacheclearsallentriesandreloadstheentriesfromthehostsfile.Task3DNSProtocolAnalysiswithWireSharkNowitistimetocaptureDNSprotocoldataanddotheanalysiswithWireShark.FollowthestepstocapturetheDNSpackets:closeallotherInternetapplicationstoreducethecaptureddatastartawebbrowseruseipconfigtoemptytheDNScacheinyourcomputerstartWireSharkprogram,andenterthedisplayfilter“ip.addr==10.66.127.1anddns”,wheretheIPaddress192.168.0.100shouldbetheIPaddressforyourcomputer.Youfinditinquestion6.StartpacketcaptureinWireSharkEntertheurladdressStopthepacketcapture.Question7:LocatetheDNSqueryandresponseforresolving找到解决查询和响应。他们是通过UDP或TCP发送？UDPQuestion8:WhatisthedestinationportfortheDNSquerymessage?WhatisthesourceportofDNSresponsemessage?DNS查询消息的目的端口是什么？什么是源端口DNS响应消息？目的端口：210.32.32.1源端口：10.66.127.1Question9:TowhatIPaddressistheDNSquerymessagesent?Useipconfigtodete