ICMP協(xié)議IP協(xié)議的缺陷ErrorReporting/ErrorcorrectingmechanismAssistancemechanism–queryInformationfromanotherhostorrouter.ICMP協(xié)議的層次ICMP消息差錯報告消息查詢消息ICMP消息格式差錯報告消息IP不關(guān)心差錯檢查和差錯控制ICMP只報告差錯，不糾錯，糾錯的處理？差錯消息總是被發(fā)送給源端。（？）差錯報告消息類型差錯報告消息對差錯報告消息，不會生成差錯報告消息去響應(yīng)。即一個差錯報告消息獨立完成一個任務(wù)。對分片報文，只有第一個分片引發(fā)差錯報告消息對多播報文，不會產(chǎn)生差錯報文對環(huán)回地址不會產(chǎn)生差錯報文差錯消息內(nèi)容為什么要加IP報文數(shù)據(jù)部分的8個字節(jié)UDP和TCP報文頭格式目的不可達消息報文Code0.Thenetworkisunreachable,possiblyduetohardwarefailure.Code1.Thehostisunreachable.Thiscanalsobeduetohardwarefailure.Code2.Theprotocolisunreachable.AnIPdatagramcancarrydatabelongingto

higher-levelprotocolssuchasUDP,TCP,andOSPF.Ifthedestinationhost

receives

adatagramthatmustbedelivered,forexample,totheTCPprotocol,but

theTCPprotocolisnotrunningatthemoment,acode2messageissent.Code3.Theportisunreachable.Theapplicationprogram(process)thatthedatagramisdestinedforisnotrunningatthemoment.Code4.Fragmentationisrequired,buttheDF(donotfragment)fieldofthedatagram

hasbeenset.Inotherwords,thesenderofthedatagramhasspecifiedthatthe

datagramnotbefragmented,butroutingisimpossiblewithoutfragmentation.Code5.Sourceroutingcannotbeaccomplished.Inotherwords,oneormorerouters

definedinthesourceroutingoptioncannotbevisited.Code6.Thedestinationnetworkisunknown.Thisisdifferentfromcode0.In

code0,therouterknowsthatthedestinationnetworkexists,butitis

unreachable

atthemoment.Forcode6,therouterhasnoinformationaboutthedestination

network.Code7.Thedestinationhostisunknown.Thisisdifferentfromcode1.Incode1,

therouterknowsthatthedestinationhostexists,butitisunreachableatthemoment.Forcode7,therouterisunawareoftheexistenceofthedestinationhost.Code8.Thesourcehostisisolated.Code9.Communicationwiththedestinationnetworkisadministratively

prohibited.Code10.Communicationwiththedestinationhostisadministrativelyprohibited.Code11.Thenetworkisunreachableforthespecifiedtypeofservice.Thisisdifferent

fromcode0.Heretheroutercanroutethedatagramifthesourcehad

requestedanavailabletypeofservice.Code12.Thehostisunreachableforthespecifiedtypeofservice.Thisisdifferent

fromcode1.Heretheroutercanroutethedatagramifthesourcehadrequestedan

availabletypeofservice.Code13.Thehostisunreachablebecausetheadministratorhasputafilteronit.Code14.Thehostisunreachablebecausethehostprecedenceisviolated.The

messageissentbyaroutertoindicatethattherequestedprecedenceisnotpermitted

forthedestination.Code15.Thehostisunreachablebecauseitsprecedencewascutoff.Thismessage

isgeneratedwhenthenetworkoperatorshaveimposedaminimumlevelofprecedencefortheoperationofthenetwork,butthedatagramwassentwithaprecedence

belowthislevel.SourceQuench消息流控制和擁賽控制報文格式TimeExceeded消息ParameterProblem消息IP頭部歧義會引起嚴(yán)重問題。路由器或主機發(fā)現(xiàn)任何頭部歧義問題時，會丟棄此數(shù)據(jù)報，并向源端報告。0頭部字段有歧義1頭部要求的選項丟失Redirection消息報文格式Code0.Redirectionforanetwork-specificroute.Code1.Redirectionforahost-specificroute.Code2.Redirectionforanetwork-specificroutebasedonaspecifiedtypeof

service.Code3.Redirectionforahost-specificroutebasedonaspecifiedtypeofservice.查詢消息用于診斷網(wǎng)絡(luò)問題現(xiàn)在只使用兩組：echorequestechoreply

timestamprequesttimestampreply.echo消息Timestamp消息兩個測試工具PINGTRACEROUTE作業(yè)111、主機A發(fā)送一個時間戳請求消息給主機B，但是沒有收到響應(yīng)，給出三個原因及主機或路由器對其采取的處理。2、主機A發(fā)送一個IP數(shù)據(jù)報給主機B。主機B沒接收到任何數(shù)據(jù)報，主機A也沒接收到任何失敗的