通信网原理实验报告记录EthernetandARP.docx
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通信网原理实验报告记录EthernetandARP
通信网原理实验报告记录EthernetandARP
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————————————————————————————————日期：
实验一EthernetandARP
一、实验目的
1.加强对以太网帧格式的理解；
2.理解ARP协议的工作原理。
二、实验环境
1.PC机一台；
2.WireShark软件。
三、实验内容
1.CapturingandanalyzingEthernetframes
2.TheAddressResolutionProtocol
四、实验步骤及思考
（一）CapturingandanalyzingEthernetframes
（1）BasedonthecontentsoftheEthernetframecontainingtheHTTPGETmessage
1.Whatisthe48-bitEthernetaddressofyourcomputer?
Answer：
The48-bitEthernetaddressofmycomputeris:
c8:
0a:
a9:
db:
9b:
f3
2.Whatisthe48-bitdestinationaddressintheEthernetframe?
IsthistheEthernetaddressofgaia.cs.umass.edu?
（Hint:
theanswerisno）.WhatdevicehasthisasitsEthernetaddress?
[Note:
thisisanimportantquestion,andonethatstudentssometimesgetwrong.Re-readpages468-469inthetextandmakesureyouunderstandtheanswerhere.]
Answer：
1）The48-bitdestinationaddressintheEthernetframeis:
00:
23:
89:
8d:
50:
71
2）ThisisnottheEthernetaddressofgaia.cs.umass.edu.
3）ItistheaddressofmyLinksysrouter,whickisthelinkusedtogetoffthesubnet.
3.Givethehexadecimalvalueforthetwo-byteFrametypefield.Whatdothebit（s）whosevalueis1meanwithintheflagfield?
Answer：
1）Thehexadecimalvalueforthetwo-byteFrametypefieldis:
ox0800
2）Thevalueis1withintheflagfieldmeansthefragmenthasnotbeenfragmented.
4.HowmanybytesfromtheverystartoftheEthernetframedoestheASCII“G”in“GET”appearintheEthernetframe?
Answer：
1）TheASCII“G”appears54bytesfromtheverystartoftheEthernetframe.
2）Calculationprocessasfollows:
Thereare14bytesofEthernetframe,20bytesofIPheaderand20bytesofTCPheaderbeforeHTTPdataisencountered.
5.WhatisthehexadecimalvalueoftheCRCfieldinthisEthernetframe?
Answer：
1）ThereisnoCRCfield.
2）BecausetheCRCcalculatedbeforetheWiresharkpacketsnifferstartup.
（2）BasedonthecontentsoftheEthernetframecontainingthefirstbyteoftheHTTPresponsemessage
6.WhatisthevalueoftheEthernetsourceaddress?
Isthistheaddressofyourcomputer,orofgaia.cs.umass.edu（Hint:
theanswerisno）.WhatdevicehasthisasitsEthernetaddress?
Answer：
1）ThevalueoftheEthernetsourceaddressis:
00:
23:
89:
8d:
50:
71
2）Thisisneithertheaddressofyourcomputer,northeaddressofgaia.cs.umass.edu.
3）ItistheaddressofmyLinksysrouter,whichisthelinkusedtogetontomysubnet.
7.WhatisthedestinationaddressintheEthernetframe?
IsthistheEthernetaddressofyourcomputer?
Answer：
1）ThedestinationaddressintheEthernetframeis:
c8:
0a:
a9:
db:
9b:
f3
2）Itistheaddressofmycomputer.
（The48-bitEthernetaddressofmycomputeris:
c8:
0a:
a9:
db:
9b:
f3）
8.Givethehexadecimalvalueforthetwo-byteFrametypefield.Whatdothebit（s）whosevalueis1meanwithintheflagfield?
Answer：
1）Thehexadecimalvalueforthetwo-byteFrametypefieldis:
0x0800.
2）Thevalueis1withintheflagfieldmeansthefragmenthasnotbeenfragmented.
9.HowmanybytesfromtheverystartoftheEthernetframedoestheASCII“O”in“OK”（i.e.,theHTTPresponsecode）appearintheEthernetframe?
Answer：
1）TheASCII“O”appears54bytesfromtheverystartoftheEthernetframe.
2）Calculationprocessasfollows:
Thereare14bytesofEthernetframe,20bytesofIPheaderand20bytesofTCPheaderbeforeHTTPdataisencountered.
10.WhatisthehexadecimalvalueoftheCRCfieldinthisEthernetframe?
Answer：
1）ThereisnoCRCfield.
2）Thereason:
BecausetheCRCcalculatedbeforetheWiresharkpacketsnifferstartup.
（二）TheAddressResolutionProtocol
（1）ARPCaching
11.Writedownthecontentsofyourcomputer’sARPcache.Whatisthemeaningofeachcolumnvalue?
Answer：
1）TheInternetAddresscolumncontainstheIPaddress,.
2）ThePhysicalAddresscolumncontainstheMACaddress,andthetypeindicatestheprotocoltype.
3）ObservingARPinaction
12.WhatarethehexadecimalvaluesforthesourceanddestinationaddressesintheEthernetframecontainingtheARPrequestmessage?
Answer：
1）ThehexadecimalvaluesforthesourceaddressesintheEthernetframecontainingtheARPrequestmessageis:
00:
23:
89:
8d:
50:
71
2）ThedestinationaddressesintheEthernetframecontainingtheARPrequestmessageis:
ff:
ff:
ff:
ff:
ff:
ff
13.Givethehexadecimalvalueforthetwo-byteEthernetFrametypefield.Whatdothebit（s）whosevalueis1meanwithintheflagfield?
Answer：
Thehexadecimalvalueforthetwo-byteEthernetFrametypefieldis:
0x0806.
14.DownloadtheARPspecificationfromftp:
//ftp.rfc-editor.org/innotes/std/std37.txt.Areadable,detaileddiscussionofARPisalsoathttp:
//www.erg.abdn.ac.uk/users/gorry/course/inet-pages/arp.html.
a）HowmanybytesfromtheverybeginningoftheEthernetframedoestheARPopcodefieldbegin?
Answer：
TheARPopcodefieldbegins20bytesfromtheverybeginningoftheEthernetframe.
b）WhatisthevalueoftheopcodefieldwithintheARP-payloadpartoftheEthernetframeinwhichanARPrequestismade?
Answer：
ThehexvalueforopcodefieldwithingtheARP-payloadoftherequestis1.
c）DoestheARPmessagecontaintheIPaddressofthesender?
Answer：
Yes,theARPmessagecontaingtheIPaddress192.168.1.105forthesender.
d）WhereintheARPrequestdoesthe“question”appear–theEthernetaddressofthemachinewhosecorrespondingIPaddressisbeingqueried?
Answer：
Thefield“TargetMACaddress”issetto00:
00:
00:
00:
00:
00toquestionthemachinewhosecorrespondingIPaddress（192.168.1.105）isbeingqueried.
15.NowfindtheARPreplythatwassentinresponsetotheARPrequest.
a）HowmanybytesfromtheverybeginningoftheEthernetframedoestheARPopcodefieldbegin?
Answer：
TheARPopcodefieldbegins20bytesfromtheverybeginningoftheEthernetframe.
b）WhatisthevalueoftheopcodefieldwithintheARP-payloadpartoftheEthernetframeinwhichanARPresponseismade?
Answer：
ThehexvalueforopcodefieldwithingtheARP-payloadpartoftheEthernetframeis2．
c）WhereintheARPmessagedoesthe“answer”totheearlierARPrequestappear–theIPaddressofthemachinehavingtheEthernetaddresswhosecorrespondingIPaddressisbeingqueried?
Answer：
TheanswertotheearlierARPrequestappearsinthe”SenderMACaddress”field,whichcontainstheEthernetaddress00:
d0:
59:
a9:
3d:
68forthesenderwithIPaddress192.168.1.1.
16.WhatarethehexadecimalvaluesforthesourceanddestinationaddressesintheEthernetframecontainingtheARPreplymessage?
Answer：
Thehexvalueforthesourceaddressis00:
06:
25:
da:
af:
73andforthedestinationis00:
d0:
59:
a9:
3d:
68.
17.Opentheethernet-ethereal-trace-1tracefilein
http:
//gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip.ThefirstandsecondARPpacketsinthistracecorrespondtoanARPrequestsentbythecomputerrunningWireshark,andtheARPreplysenttothecomputerrunningWiresharkbythecomputerwiththeARP-requestedEthernetaddress.Butthereisyetanothercomputeronthisnetwork,asindiatedbypacket6–anotherARPrequest.WhyistherenoARPreply（sentinresponsetotheARPrequestinpacket6）inthepackettrace?
Answer：
Thereisnoreplyinthistrace,becausewearenotatthemachinethatsenttherequest.TheARPrequestisbroadcast,buttheARPreplyissentbackdirectlytothesender’sEthernetaddress.
五、实验结论
1.CRC在WireShark中是不能被抓到的，原因是CRC在抓包之前已经被计算好。
2.ARPRequest消息的Type字段值为1；ARPReplyt消息的Type字段值为2。
3.MACaddress是唯一的。
4.清空ARP缓存时（ARP–d）会出现如下的情况：
5.ARP–a可以查看ARP缓存中的内容。
六、实验总结
通过这次实验，我对ARP协议有了进一步的理解，在实验过程中遇到了许多问题，但经过查阅资料并和学姐交流，最终解决了这些问题，以实验的方式验证课本上的理论知识，学习也变得更有意义。
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