计算机网络实验2WiresharkDNS.docx
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计算机网络实验2WiresharkDNS.docx
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计算机网络实验2WiresharkDNS
Lab2
1.nslookup
1.RunnslookuptoobtaintheIPaddressofaWebserverinAsia.
Theaddressis202.38.193.188
2.RunnslookuptodeterminetheauthoritativeDNSserversforauniversityinEurope.
TherearefourauthoritativeDNSservers.
3.RunnslookupsothatoneoftheDNSserversobtainedinQuestion2isqueriedforthemailserversforYahoo!
mail.
Thequeryisfailed.
3.TracingDNSwithWireshark
STEPS
•UseipconfigtoemptytheDNScacheinyourhost.
•Openyourbrowserandemptyyourbrowsercache.(WithInternetExplorer,gotoToolsmenuandselectInternetOptions;thenintheGeneraltabselectDeleteFiles.)
•OpenWiresharkandenter“ip.addr==your_IP_address”intothefilter,whereyouobtainyour_IP_address(theIPaddressforthecomputeronwhichyouarerunningWireshark)withipconfig.Thisfilterremovesallpacketsthatneitheroriginatenoraredestinedtoyourhost.
•StartpacketcaptureinWireshark.
•Withyourbrowser,visittheWebpage:
http:
//www.ietf.org
•Stoppacketcapture.
QUESTIONS
4.LocatetheDNSqueryandresponsemessages.AretheysentoverUDPorTCP?
TheyaresentoverUDP.
5.WhatisthedestinationportfortheDNSquerymessage?
WhatisthesourceportofDNSresponsemessage?
ThedestinationportfortheDNSquerymessageis53.ThesourceportofDNSresponsemessageis53.
6.TowhatIPaddressistheDNSquerymessagesent?
UseipconfigtodeterminetheIPaddressofyourlocalDNSserver.ArethesetwoIPaddressesthesame?
TheDNSquerymessageissentto202.116.64.114.TheIPaddressofmylocalDNSserveris202.116.64.114.ThesetwoIPaddressesarethesame.
7.ExaminetheDNSquerymessage.What“Type”ofDNSqueryisit?
Doesthequerymessagecontainany“answers”?
The“Type”is‘A’.Thequerymessagedoesn’tcontainany“answers”.
8.ExaminetheDNSresponsemessage.Howmany“answers”areprovided?
Whatdoeseachoftheseanswerscontain?
3“answers”areprovided.ThefirstonecontainsName,Type,Class,Timetolive,Datalength,CNAME.ThelasttwocontainsName,Type,Class,Timetolive,Datalength,Address.
9.ConsiderthesubsequentTCPSYNpacketsentbyyourhost.DoesthedestinationIPaddressoftheSYNpacketcorrespondtoanyoftheIPaddressesprovidedintheDNSresponsemessage?
TheIPaddressesprovidedintheDNSresponsemessageare104.20.0.85and104.20.1.85.ButthereisnotaSYNpacketofwhichthedestinationIPaddresscorrespondtoanyofthem.
10.Thiswebpagecontainsimages.Beforeretrievingeachimage,doesyourhostissuenewDNSqueries?
Myhostdoesn’tissuenewDNSqueries.
STEPS
•Startpacketcapture.
•Doannslookupon“”
•Stoppacketcapture.
QUESTIONS
11.WhatisthedestinationportfortheDNSquerymessage?
WhatisthesourceportofDNSresponsemessage?
ThedestinationportfortheDNSquerymessageis53.ThesourceportofDNSresponsemessageis53.
12.TowhatIPaddressistheDNSquerymessagesent?
IsthistheIPaddressofyourdefaultlocalDNSserver?
TheIPaddressis202.116.64.114.ThisistheIPaddressofmydefaultlocalDNSserver.
13.ExaminetheDNSquerymessage.What“Type”ofDNSqueryisit?
Doesthequerymessagecontainany“answers”?
Thetypeis‘A’.Thequerymessagedoesn’tcontainany“answers”.
14.ExaminetheDNSresponsemessage.Howmany“answers”areprovided?
Whatdoeseachoftheseanswerscontain?
Oneanswerisprovided.ItcontainsName,Type,Class,Timetolive,Datalength,Address.
15.Provideascreenshot.
STEPS
•Startpacketcapture.
•Enterthecommand“nslookup-type=NS”
•Stoppacketcapture.
QUESTIONS
16.TowhatIPaddressistheDNSquerymessagesent?
IsthistheIPaddressofyourdefaultlocalDNSserver?
TheIPaddressis202.116.64.114.ThisistheIPaddressofmydefaultlocalDNSserver.
17.ExaminetheDNSquerymessage.What“Type”ofDNSqueryisit?
Doesthequerymessagecontainany“answers”?
Thetypeis“NS”.Thequerymessagedoesn’tcontainany“answers”.
18.ExaminetheDNSresponsemessage.WhatFUDANnameserversdoestheresponsemessageprovide?
DoesthisresponsemessagealsoprovidetheIPaddressesoftheFUDANnameservers?
NoIPaddress.
19.Provideascreenshot.
STEPS
•Startpacketcapture.
•Enterthecommand“nslookup”
•Stoppacketcapture.
QUESTIONS
20.TowhatIPaddressistheDNSquerymessagesent?
IsthistheIPaddressofyourdefaultlocalDNSserver?
Ifnot,whatdoestheIPaddresscorrespondto?
202.120.224.26.Thisisn’ttheIPaddressofmydefaultlocalDNSserver.TheIPaddresscorrespondto.
21.ExaminetheDNSquerymessage.What“Type”ofDNSqueryisit?
Doesthequerymessagecontainany“answers”?
Thetypeis‘A’.Thequerymessagedoesn’tcontainany“answers”.
22.ExaminetheDNSresponsemessage.Howmany“answers”areprovided?
Whatdoeseachoftheseanswerscontain?
2answersareprovided.ThefirstonecontainsName,Type,Class,Timetolive,Datalength,CNAME.ThesecondonecontainsName,Type,Class,Timetolive,Datalength,Address.
23.Provideascreenshot.
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