计网实验DNS--Data-Encapsulation-and-Frame-Examination

ComputernetowrksLabs1ComputernetowrksLabsDNS,DataEncapsulationandFrameExaminationDNS,DataEncapsulationandFrameExaminationLearningObjectivesAtcompletionofthislab,youwillbeableto:1.UseWiresharktocaptureandanalyzeDNSmessage2.UnderstandhowDNSworks3.usenslookupandipconfigcommands4.ExplaintheheaderfieldsinanEthernetIIframe.5.understanddataencapsulationComputernetowrksLabs26.ReportandFeedbackonthislabAnswerallquestionswithsupportingscreenshots.Pleasefillinthefollowingfeedbackformandappendittothereport.Yourfeedbackisvaluabletoussothatwecanimprovethislab,andmakethecoursewelcome.Foreachtask,pleaseratethefollowinginthescaleof1through5:Thedegreeofdifficulty:1=tooeasy;5=toodifficultThelearningexperience:1=learnednothing;5=learnedalotYourinterest:1=nointerest;5=highinterestTimeusedforthetask:inminutesTaskDifficulty(1—5)Learning(1—5)Interest(1—5)Time(min)Task0Task1Task2Task3Task4Yoursuggestion/comment:BackgroundWhenupperlayerprotocolscommunicatewitheachother,dataatthesendinghostflowsdowntheTCP/IPprotocollayersandisencapsulatedintoaprotocoldataunitatlowerlayer,andfinallyencapsulatedinaLayer2frame.Forexample,DNSmessageisoftentransportedbyUDPprotocolonlayer4.SoDNSmessageatthesendinghostisencapsulatedinaUDPsegment;theUDPsegmentisthenencapsulatedinanIPpacket,andtheIPpacketisencapsulatedfinallyinalayer2frame.Theframecompositionisdependentonthemediaaccesstype,orthenetwork.Forexample,ifthemediaaccessisEthernet,thentheLayer2frameencapsulationwillbeEthernetII.Whenlearningaboutdataencapsulationandprotocoloperations,itishelpfultoanalyzetheheaderinformationfoundintheprotocoldataunits.TheDNSprotocoloperation,ipconfigcommand,andEthernetIIframeheaderwillbeexaminedinthislab.EthernetIIframescansupportvariousupperlayerprotocols.Formorebackgroundinformation,pleasereadthelectures02,04-05,10,11.ComputernetowrksLabs3TasksTask0ProtocolLayersandDataEncapsulationAswehavediscussedinLecture02,Internetisinter-connectednetworksbasedonTCP/IPprotocols.Readtheslidesortextbooktolearnhowdatagoesthroughprotocollayersandhowdataisencapsulatedintheprotocoldataunits.Thereareconventionalnamesfortheprotocoldataunitsfordifferentlayerprotocols.Question1.Whatarenamesfortheprotocoldataunits(PDUs)forlayer4,layer3,andlayer2protocolsinTCP/IPreferencemodelbyfillingthefollowform: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:ComputernetowrksLabs4Question2:WhatistheDNSserverIPaddressthatisusedtoqueryandfindIPaddressfor“nslookup-type=NShdu.edu.cn”,andcapturetheoutput,asIdidandshowedbelow:Question3:Whataredomainnameserversforhdu.edu.cnandtheirIPaddresses?Typethecommand“nslookup”,andcapturetheoutput,asIdidandshowedbelow:Question4:WhichDNSserverisusedtoqueryandfornameresolution?YoucanalsousenslookuptofindthemappingfromIPaddressestothehostnames.Typethecommands“nslookup192.168.156.101”and“nslookupcourse.comm.hdu.edu.cn”,andcapturetheoutput,asIdidandshowedbelow:ComputernetowrksLabs5Question5:Canahosthavemultiplehostnames?WhatistheIPaddressformoodle.tec.hkr.se?HowmanynamesdoyoufindforthisIPaddress?Task2DNSandipconfigipconfig(forWindows)andifconfig(forLinux/Unix,interfaceconfiguration)areamongthemostusefultoolsfordebuggingnetworkissues.ipconfigcanbeusedtoshowyourcurrentTCP/IPinformation,includingyouraddress,DNSserveraddresses,adapter(networkinterfacecard)typeandsoon.Forexample,ifyouwanttofindallthisinformationaboutyourhost,simplyenterthecommand“ipconfig/all”inthecommandline.Readmoreon“usingipconfig”at:WhatistheIPaddressforyourcomputer,andwhatisthelocalDNSserverIPaddress?答:IP:192.168.1.143ComputernetowrksLabs6DNS:210.32.32.10210.32.32.11ipconfigisalsoveryusefulformanagingtheDNSinformationstoredinyourhost.Toimprovethenetworkingperformance,ahostcancacheDNSrecordsitrecentlyobtained.Toviewthesecachedrecords,youcanusethecommand“ipconfig/displaydns”.EachentryshowstheremainingTimetoLive(TTL)inseconds.Toclearthecache,enterthecommand“ipconfig/flushdns”.FlushingtheDNScacheclearsallentriesandreloadstheentriesfromthehostsfile.Task3DNSProtocolAnalysiswithWireSharkNowitistimetocaptureDNSprotocoldataanddotheanalysiswithWireShark.FollowthestepstocapturetheDNSpackets:closeallotherInternetapplicationsto