计算机网络实验4Wireshark Lab ICMP.docx

计算机网络实验4Wireshark Lab ICMP.docx

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计算机网络实验4WiresharkLabICMP

Lab4WiresharkLab:

ICMP

STEPS

•Let’sbeginthisadventurebyopeningtheWindowsCommandPromptapplication（whichcanbefoundinyourAccessoriesfolder）.

•StartuptheWiresharkpacketsniffer,andbeginWiresharkpacketcapture.

•Thepingcommandisinc:

\windows\system32,sotypeeither“ping–n10hostname”or“c:

\windows\system32\ping–n10hostname”intheMS-DOScommandline（withoutquotationmarks）,wherehostnameisahostonanothercontinent.Ifyou’reoutsideofAsia,youmaywanttoenterwww.ust.hkfortheWebserveratHongKongUniversityofScienceandTechnology.Theargument“-n10”indicatesthat10pingmessagesshouldbesent.ThenrunthePingprogrambytypingreturn.

•WhenthePingprogramterminates,stopthepacketcaptureinWireshark.

QUESTIONS

1、WhatistheIPaddressofyourhost?

WhatistheIPaddressofthedestinationhost?

TheIPaddressofmyhostis172.18.40.131.TheIPaddressofthedestinationhostis143.89.14.2.

2、WhyisitthatanICMPpacketdoesnothavesourceanddestinationportnumbers?

BecausethattheICMPisaprotocolinnetworklayer,anditisdesignedtocommunicateinformationinnetworklayerbetweenhostsandrouters,ratherthanapplicationlayerprocesses.WehavetonoticethateachICMPpackethasa“Type”and“Code”field.Theywillidentifiesthemessagebeingreceived.NetworksoftwarecanunderstandtheICMPmessage.SoICMPpacketdoesnotneedtohavesourceanddestinationportnumbers.

3、Examineoneofthepingrequestpacketssentbyyourhost.WhataretheICMPtypeandcodenumbers?

WhatotherfieldsdoesthisICMPpackethave?

Howmanybytesarethechecksum,sequencenumberandidentifierfields?

TheICMPtypeis8,andthecodenumbersis0.ThisICMPpacketstillhaveChecksum、Identifier、Sequencenumberanddatafields.Checksumfieldhas2bytes.Sequencenumberfieldshas2bytes.Identifierfieldhas2bytes.

4、Examinethecorrespondingpingreplypacket.WhataretheICMPtypeandcodenumbers?

WhatotherfieldsdoesthisICMPpackethave?

Howmanybytesarethechecksum,sequencenumberandidentifierfields?

TheICMPtypeis0,andthecodenumbersis0.TheICMPpacketstillhaveChecksum、Identifier、Sequencenumberanddatafields.Checksumfieldhas2bytes.Sequencenumberfieldshas2bytes.Identifierfieldhas2bytes.

STEPS

•Let’sbeginbyopeningtheWindowsCommandPromptapplication（whichcanbefoundinyourAccessoriesfolder）.

•StartuptheWiresharkpacketsniffer,andbeginWiresharkpacketcapture.

•Thetracertcommandisinc:

\windows\system32,sotypeeither“tracerthostname”or“c:

\windows\system32\tracerthostname”intheMS-DOScommandline（withoutquotationmarks）,wherehostnameisahostonanothercontinent.（NotethatonaWindowsmachine,thecommandis“tracert”andnot“traceroute”.）Ifyou’reoutsideofEurope,youmaywanttoenterwww.inria.frfortheWebserveratINRIA,acomputerscienceresearchinstituteinFrance.ThenruntheTracerouteprogrambytypingreturn.

•WhentheTracerouteprogramterminates,stoppacketcaptureinWireshark.

QUESTIONS

5.WhatistheIPaddressofyourhost?

WhatistheIPaddressofthetargetdestinationhost?

TheIPaddressofmyhostis172.18.40.131.TheIPaddressofthetargetdestinationhostis128.93.162.84

6.IfICMPsentUDPpacketsinstead（asinUnix/Linux）,wouldtheIPprotocolnumberstillbe01fortheprobepackets?

Ifnot,whatwoulditbe?

TheIPprotocolnumberwouldn’tstillbe01fortheprobepackets.Itwouldbe17.

7.ExaminetheICMPechopacketinyourscreenshot.IsthisdifferentfromtheICMPpingquerypacketsinthefirsthalfofthislab?

Ifyes,howso?

TheICMPechopackethasthesamefieldsasthepingquerypacket.Butthedatafield’ssizeisdifferent.TheICMPpingquerypackets’datafieldsizeis32bytes.ButthesizeofdatafieldinICMPechopacketisnotthenumber.

ICMPechopacket

ICMPpingquerypackets

8.ExaminetheICMPerrorpacketinyourscreenshot.IthasmorefieldsthantheICMPechopacket.Whatisincludedinthosefields?

Itcontainstheheaderandthefirst8bytesoftheIPdatagramthatcausetheICMPmessagetobegenerated.Besides,wecanseethatithastheoriginalICMPmessage,andithasownType、CodeandChecksumfields.

ICMPechopacket

ICMPerrorpacket

9.ExaminethelastthreeICMPpacketsreceivedbythesourcehost.HowarethesepacketsdifferentfromtheICMPerrorpackets?

Whyaretheydifferent?

ThelastthreeICMPpackets’typeis0ratherthan11.ThatmeanstheICMPpacketisanechoreplypacket.TheyaredifferentbecausethatthelastthreeICMPpackethavearrivedthedestinationbeforetheTTLexpired..

ICMPerrorpackets

thelastthreeICMPpackets

10.Withinthetracertmeasurements,istherealinkwhosedelayissignificantlylongerthanothers?

RefertothescreenshotinFigure4,istherealinkwhosedelayissignificantlylongerthanothers?

Onthebasisoftherouternames,canyouguessthelocationofthetworoutersontheendofthislink?

Inthepicture,wecanseethatalinkbetweenstep12andstep13hasasignificantlydelaylongerthanothers.Butsadly,wecan’tgettheroutername,soit’shardtogettheinformationabouttheirlocation.ButwecansearchthemontheInternet.WhatsurprisemeisthatbothofthemareinChina,whichmeansthattheyarenotindifferentcountry.InFigure4,wecanseethatalinkbetweenstep9andstep10hasasignificantlydelaylongerthanothers.Basedontheroutername,IcanguessthelinkisfromNewYorkCitytoPastourelle,France.

QUESTIONS

ForoneoftheprogrammingassignmentsyoucreatedaUDPclientpingprogram.Thispingprogram,unlikethestandardpingprogram,sendsUDPprobepacketsratherthanICMPprobepackets.UsetheclientprogramtosendaUDPpacketwithanunusualdestinationportnumbertosomelivehost.Atthesametime,useWiresharktocaptureanyresponsefromthetargethost.ProvideaWiresharkscreenshotfortheresponseaswellasananalysisoftheresponse.

Mycomputerruntheclient,andtheIPaddressis172.18.40.131.Anothercomputerruntheserver,andtheIPaddressis172.18.43.93,andtheportnumberis1048.SoIgettheWiresharkscreenshotasthefollow.

Theclient’sinformationisfollow.

WecangetthattheminimumRTTsis6ms.ThemaximumRTTsis264ms.TheaverageRTTsis132.9ms.Inthiscondition,Packet2islostorthereplyforpacket2islost,sopacket2didn’tgetreply.Butotherpacketgettheirreply.

Thecodeforclientisfollow.

importjava.io.*;

import.*;

importjava.util.*;

importjava.text.SimpleDateFormat;

publicclassPingClient

{

privatestaticfinaldoubleLOSS_RATE=0.3;

privatestaticfinalintAVERAGE_DELAY=100;//milliseconds

publicstaticvoidmain（String[]args）throwsException

{

if（args.length!

=2）

{

System.out.println（"Requiredarguments:

hostport"）;

return;

}

Stringhost=args[0].toString（）;

intport=Integer.parseInt（args[1]）;

//建立socket

DatagramSocketclientSocket=newDatagramSocket（）;

//等待1秒钟

clientSocket.setSoTimeout（1000）;

InetAddressIPAddress=InetAddress.getByName（host）;

for（inti=0;i<10;i++）

{

//发送报文

byte[]sendData=newbyte[1024];

byte[]receiveData=newbyte[1024];

DatecurrentTime=newDate（）;

SimpleDateFormatformatter=newSimpleDateFormat（"yyyy-MM-ddHH:

mm:

ss:

SSS"）;

StringtimeStamp=formatter.format（currentTime）;

StringpingMessage="PING"+i+""+timeStamp+""+"\r\n";

sendData=pingMessage.getBytes（）;

DatagramPacketsendPacket=newDatagramPacket（sendData,sendData.length,IPAddress,port）;

try

{

DatecurTime1=newDate（）;

clientSocket.send（sendPacket）;

DatagramPacketreceivePacket=newDatagramPacket（receiveData,receiveData.length）;

clientSocket.receive（receivePacket）;

DatecurTime2=newDate（）;

printData（receivePacket）;

System.out.println（"RTT:

"+（curTime2.getTime（）-curTime1.getTime（））+"ms"）;

}

catch（.SocketTimeoutExceptionex）

{

System.out.println（"NoReplyFromServer!

"）;

}

}

clientSocket.close（）;

}

privatestaticvoidprintData（DatagramPacketreceivePacket）throwsException

{

//Obtainreferencestothepacket'sarrayofbytes.

byte[]buf=receivePacket.getData（）;

//Wrapthebytesinabytearrayinputstream,sothatyoucanreadthedataasastream

//ofbytes.

ByteArrayInputStreambais=newByteArrayInputStream（buf）;

//Wrapthebytearrayoutputstreaminaninputstreamreader,

//soyoucanreadthedataasastreamofcharacters.

InputStreamReaderisr=newInputStreamReader（bais）;

//Wraptheinputstreamreaderinabufferedreader,

//soyoucanreadthecharacterdataalineatatime.

//（Alineisasequenceofcharsterminatedbyanycombinationof\rand\n.）

BufferedReaderbr=newBufferedReader（isr）;

//Themessagedataiscontainedinasingleline,soreadthisline.

Stringline=br.readLine（）;

//Printhostaddressanddatareceivedfromit.

System.out.println（"PacketFromServer"+":

"+newString（line））;

}

}