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1/130ExamAQUESTION1Refertotheexhibit.WhatwillRouter1dowhenitreceivesthedataframeshown?(Choosethree.)A.Router1willstripoffthesourceMACaddressandreplaceitwiththeMACaddress0000.0c36.6965.B.Router1willstripoffthesourceIPaddressandreplaceitwiththeIPaddress192.168.40.1.C.Router1willstripoffthedestinationMACaddressandreplaceitwiththeMACaddress0000.0c07.4320.D.Router1willstripoffthedestinationIPaddressandreplaceitwiththeIPaddressof192.168.40.1.E.Router1willforwardthedatapacketoutinterfaceFastEthernet0/1.F.Router1willforwardthedatapacketoutinterfaceFastEthernet0/2.CorrectAnswer:ACFSection:part1ExplanationExplanation/Reference:考点：数据通信过程源目IP/mac地址的变化。Age(min)下面-为本地端口A：源MAC替换为f0/2口的mac，正确B：替换源IP，错误C：替换目的mac为下一跳入口的MAC，正确D：替换目的IP，错误E：从f0/1转发数据，错误F：正确QUESTION2Refertotheexhibit.WhichthreestatementscorrectlydescribeNetworkDeviceA?(Choosethree.)2/130A.Withanetworkwidemaskof255.255.255.128,eachinterfacedoesnotrequireanIPaddress.B.Withanetworkwidemaskof255.255.255.128,eachinterfacedoesrequireanIPaddressonauniqueIPsubnet.C.Withanetworkwidemaskof255.255.255.0,mustbeaLayer2deviceforthePCstocommunicatewitheachother.D.Withanetworkwidemaskof255.255.255.0,mustbeaLayer3deviceforthePCstocommunicatewitheachother.E.Withanetworkwidemaskof255.255.254.0,eachinterfacedoesnotrequireanIPaddress.CorrectAnswer:BDESection:part1ExplanationExplanation/Reference:如图，哪三个选项正确的描述了网络设备A？考点分析：这题考的是子网掩码的问题。使用掩码255.255.255.128和255.255.255.0时，两台主机的IP地址属于两个网段，所以A要用路由器（三层设备）才能通信，所以A设备每个接口需要设置IP地址。使用掩码255.255.254.0是，两台主机属于同一个网段，所以A要使用switch或hub就能通信，且不需要ip地址QUESTION3WhichlayerintheOSIreferencemodelisresponsiblefordeterminingtheavailabilityofthereceivingprogramandcheckingtoseeifenoughresourcesexistforthatcommunication?A.transportB.networkC.presentationD.sessionE.applicationCorrectAnswer:ESection:part1ExplanationExplanation/Reference:OSI中那一层负责决定一个进程的可用性并查看是否有可用的资源分给该进程？考点分析：OSI七层参考模型中负责决定一个进程的可用性并查看是否有可用的资源分给该进程是第七层应用层QUESTION4WhichofthefollowingdescribestherolesofdevicesinaWAN?(Choosethree.)A.ACSU/DSUterminatesadigitallocalloopB.Amodemterminatesadigitallocalloop3/130C.ACSU/DSUterminatesananaloglocalloopD.AmodemterminatesananaloglocalloopE.ArouteriscommonlyconsideredaDTEdeviceF.ArouteriscommonlyconsideredaDCEdeviceCorrectAnswer:ADESection:part1ExplanationExplanation/Reference:SU/DSU是用于连接终端和数字专线的设备，属于DCE设备modem用于数字信号和模拟信号的转换，属于DCE设备路由器一般是DTE设备QUESTION5Refertotheexhibit,HostApingsinterfaceS0/0onrouter3,whatistheTTLvalueforthatping?A.253B.252C.255D.254CorrectAnswer:ASection:part1ExplanationExplanation/Reference:默认是255，每经过一个路由器减1QUESTION6AnetworkadministratorisverifyingtheconfigurationofanewlyinstalledhostbyestablishinganFTPconnectiontoaremoteserver.Whatisthehighestlayeroftheprotocolstackthattheneworkadministratorisusingforthisoperation?4/130A.applicationB.presentationC.sessionD.transportE.internetF.datalinkCorrectAnswer:ASection:part1ExplanationExplanation/Reference:HTTP、FTP、TELNET、SNMP、DNS等服务都是在应用层QUESTION7Refertotheexhibit.AfterHostApingsHostB,whichentrywillbeintheARPcacheofHostAtosupportthistransmission?A.B.C.5/130D.E.F.CorrectAnswer:DSection:part1ExplanationExplanation/Reference:问：当主机Aping主机B之后，下面那个ARP缓存条目会支持此次通讯？考题分析：这道题考的是局域网ARP的请求。HostA要pingHostB，首先HostA需要封装ping包，而封装ping包需要HostA和HostB的二、三层地址的信息。然而HostA不知道HostB的二层地址，这样HostA就会向局域网发送Arp请求，来请求HostB的二层地址。网关收到HostA的Arp请求后，发现HostB是其他网段的地址，这样网关会启用代理Arp的功能，将自己的二层地址应答给HostA。HostA收到应答包后会对本地的ARP缓存进行更新，将应答方的IP和MAC地址存储在ARP缓存中，同时完成ping包的封装。网关在收到ping包后会自动完成二层地址的重定向。所以答案是D。此题考查的是pc的arp表，不要和包的目的地址、源地址弄混了。在以太网寻址的时候，依靠的事MAC地址，每一个网段都需要寻找到自己的下一条（gateway）以自己的MAC作为sourcegateway的mac作为destination封装Frame，然后将Frame转发出去，但是数据包是不会进行变化的，也就是packet的头部信息不会发生改变。所以IP包头的source和des地址是不会变更的QUESTION8Anetworkinterfaceporthascollisiondetectionandcarriersensingenabledonasharedtwistedpairnetwork.Fromthisstatement,whatisknownaboutthenetworkinterfaceport?A.Thisisa10Mb/sswitchport.B.Thisisa100Mbsswitchport.C.ThisisanEthernetportoperatingathalfduplex.D.ThisisanEthernetportoperatingatfullduplex.E.ThisisaportonanetworkinterfacecardinaPC.CorrectAnswer:CSection:part1ExplanationExplanation/Reference:考点：考查冲突域的概念。在半双工网络中才存在冲突域。综上所述选CQUESTION9Areceivinghostcomputesthechecksumonaframeanddeterminesthattheframeisdamaged.Theframeisthendiscarded.AtwhichOSIlayerdidthishappen?A.sessionB.networkC.physicalD.datalinkE.transport6/130CorrectAnswer:DSection:part1ExplanationExplanation/Reference:帧的处理是在二层QUESTION10WhichofthefollowingcorrectlydescribestepsintheOSIdataencapsulationprocess?(Choosetwo.)A.Thetransportlayerdividesadatastreamintosegmentsandmayaddreliabilityandflowcontrolinformation.B.ThedatalinklayeraddsphysicalsourceanddestinationaddressesandanFCStothesegment.C.Packetsarecreatedwhenthenetworklayerencapsulatesaframewithsourceanddestinationhostaddressesandprotocol-relatedcontrolinformation.D.PacketsarecreatedwhenthenetworklayeraddsLayer3addressesandcontrolinformationtoasegment.E.Thepresentationlayertranslatesbitsintovoltagesfortransmissionacrossthephysicallink.CorrectAnswer:ADSection:part1ExplanationExplanation/Reference:传输层将数据分段，并且加入flowcontrol等信息。在网络层就将数据进行打包，并加上ip包头，链路层