2021思科认证考试题库8节

2021思科认证考试题库精选8节第1节

在相距几百英里的路由器之间使用租用线路的点到点WAN链路上，下列哪个

设备室DCE设备

A.路由器

B.CSU/DSU

C用话局中心机房设备

D.路由器处理器上的芯片

正确答案：B

下面是你在一台交换机上执行命令showspanning-tree时得到的输出:请问下面

哪两种有关这台交换机的说法是正确的?()

A.这台交换机是根网桥

B这台交换机不是根网桥

C根网桥与这台交换机之间有4台交换机

D.这台交换机运行的是802.1W

E.这台交换机运行的是STPPVST+

答案：BD

下图中如果允许/24和10.000/8的网络之间通信,必须要配置的

两条命令是什么()

/8

「B一

A.A(config)iproute

B.A(config)iprouteS0/0/0

C.A(config)iproute

D.B(config)iproute

E.B(config)iproute

F.Biproute192.168.1,0

正确答案：AD

Whichoneofthefollowingcharacteristicsistrueregardingtheuseofhubs

andswitches?

A.HubscanhavetheirportsbeconfiguredwithVLANs

B.Usinghubsiscostlywithregardtobandwidthavailability.

C.Switchescannotforwardbroadcasts.

D.Switchesaremoreefficientthanhubsinprocessingframes.

E.Switchesincreasethenumberofcollisiondomainsinthenetwork.

正确答案：E

解析：

Explanation:Switchesincreasesthenumberofcollisionsdomainsinthenetwork.Switch

esthatareconfiguredwithVLANswillreducethesizeofthecollisiondomainsbyincreasin

gthenumberofcollisiondomainsinanetwork,butmakingthemsmallerthanthatofoneb

ig,flatnetwork.IncorrectAnswers:A.SwitchesarecapableofVLANconfigurations,buth

ubsarenot.B.Hubsaregenerallytheleastcostlymethodpossibletoconnectmultipledev

icestogetherinanetwork.C.Switchesforwardbroadcastsandmulticasts,bydefault,toall

portswithinthesameVLAN.Onlyroutersblockallbroadcasttrafficbydefault.D.Switches

andhubscanbeequallyefficientinprocessingframes,intheory.Inpractice,switchesareg

enerallymoreefficientastheyusuallyhavemoreCPUanclmemoryallocatecltothem,and

aregenerallymuchmoreexpensivethanasimplehub.

将路由器的许可证删除包括哪两步?()

A.使用命令eraseflashJicense

B.重启系统

C.使用命令licenseboot,并在末尾指定关键字disable

D.使用命令licenseclear将许可证清除

答案：CD

2021思科认证考试题库精选8节第2节

SplithorizonhasbeenenabledwithintheEzonexamroutednetwork.Which

oneofthefollowingstatementsbestexplainsthesplithorizonrule?

A.Onlyrouterscansplitboundaries(horizons)betweennetworksin

separateASnumbers.

B.EachASmustkeeproutingtablesconvergedtopreventdeadroutes

frombeingadvertisedacrossboundaries.

C.Oncearouteisreceivedonaninterface,advertisethatrouteas

unreachablebackoutthesameinterface.

D.Informationaboutarouteshouldneverbesentbackinthedirection

fromwhichtheoriginalupdatecame.

E.Noneoftheabove

正确答案：D

解析:Explanation:

Thesplithorizonrulestates:

*Neveradvertisearouteoutoftheinterfacethroughwhichyoulearnedit.

Forinstance,inFigure4abelow,ifRouterOneisconnectedtoRoutersTwoand

Threethroughasinglemultipointinterface(suchasFrame.Relay),andRouter

OnelearnedaboutNetworkAfromRouterTwo,itwillnotadvertisetherouteto

NetworkAbackoutthesameinterfacetoRouterThree.Routeroneassumesthat

RouterThreewouldlearnaboutNetworkAdirectlyfromRouterTwo.

IncorrectAnswers:

A:Thereisnosuchrequirement

B:Distancevectorprotocolsupdatesroutingtableatregularintervalsinsteadof

Topologychanges

C:Thisisthedefinitionofthepoisonreverserule,notthesplithorizonrule.

请参见图示。管理员注意到从ISP处进入网络的流量大幅增加。管理员清除了

计数器。几分钟之后，管理员又检查access-list表。从图中的输出可得出什么结论

0

R2*showaccess-lists

ExtendedIPaccesslists175

10denyicmpanyanyecho(1786matches)

20permittcpanyhost45eqwww(21matches)

30permittcpanyhost43eqpop3(189matches)

40permittcpanyhost43eqsmtp(133matches)

A.少量HTTP流量表明web服务器未正确配置

B.较高的POP3流量（与SMTP流量相比）表明企业中POP3电子邮件客户端

的数量比SMTP客户端数量多

C.大量ICMP流量在接口处被拒绝，这是受到DoS攻击的迹象

D.较高的电子邮件流量（与web流量相比）表明攻击目标主要是电子邮件服

务器

正确答案：C

AEzonexamEthernetswitchreceivesaunicastframe,withadestinationMAC

thatislistedintheswitchtable.Whatwillthisswitchdowiththeframe?

A.Theswitchwillforwardtheframe,toaspecificport

B.Theswitchwillforwardtheframe,toallportsexcepttheportonwhichit

wasreceived

C.Theswitchwillreturnacopyoftheframe,outthesourceport

D.Theswitchwillnotforwardunicastframes

E.TheswitchwillremovethedestinationMACfromtheswitchtable

F.Noneoftheabove.

正确答案：A

A解析：Explanation:

HowDoestheSwitchFindHostMACs?

Let'susethediagrambelowtohelpusunderstandhowaddresslearningprocess

takesplace.

DataLinkAddressLearning

Mactable

FEO/O:0000.74a3.0023

/FE0/11:0000.43C5.334C

Let'sassumethatwehavejustpoweredontheswitch.IthasnothinginitsMAC

table.Weconnectthecablesfromthehostsontheswitchinterfacesasshownin

thediagram.HostAinitiatesaconnectiontowardsHostD,andthefollowing

takesplace:

1.HostA(interfacefeO/O)sendsaframe,toHostD(MAC

address:0000.43c5.334c).

2.TheswitchinspectstheSourceAddressintheframe,andnotesinitstablethe

MACaddressofHostAalongwiththeInterfacenumberfromwhichtheframe,

originated.

3.TheswitchinspectstheDestinationAddressintheframe.Sinceitdoesnot

haveHostsDMACaddressinitstable,itconstructsabroadcastframe,and

forwardsoutallinterfacesexcepttheinterfacefromwheretheoriginalframe,

arrived.

4.HostDidentifiesitselfastheexpectedrecipientandrespondsbacktoHostA.

Theswitchreceivestherespondframe,oninterfacefeO/11andplacestheSAin

itstablealongwiththeinterfacenumberwheretheframe,camefrom.

5.Fromnowon,furthercommunicationbetweenthetwohostswillbeswitched

totheappropriateinterfacesbasedontheMACtablesentries.

Thisprocesstakesplaceeverytimeanewhostisattachedontheswitchand

initiatestraffic.TheswitchtriestokeepitsMACtableup-to-date,thereforeif

somehostsdonotinitiatetrafficforacertainamountoftime,theswitchremoves

themfromitstableandreinsertsthemwhentheybeginsendingtraffic.

YouneedsubnetaEzonexamnetworksegment.Howmanysubnetworksand

hostsareavailablepersubnetifyouapplya/28masktotheclassC

network?

A.30networksand6hosts.

B.6networksand30hosts.

C.8networksand32hosts.

D.32networksand18hosts.

E.16networksand14hosts.

F.Noneoftheabove

正确答案：E

E解析：Explanation:

A28bitsubnetmask(11111111.11111111.11111111.11110000)appliedtoaclass

Cnetworkusesa4bitsfornetworks,andleaves4bitsforhosts.Usingthe2n-2

formula,wehave24-2(or2x2x2x2-2)whichgivesus14forthenumberofhosts,

andthenumberofnetworksis24=16.

IncorrectAnswers:

A.Thiswouldbetheresultofa/29(48)network.

B.Thiswouldbetheresultofa/27(24)network.

C.Thisisnotpossible,aswemustsubtracttwofromthesubnetsandhostsfor

thenetworkandbroadcastaddresses.

D.Thisisnotapossiblecombinationofnetworksandhosts.

Barney是子网/24中一个具有IP地址1QLL1的主机。以下哪些操作

时标准IPACL可配置来执行的()

A.匹配准确的源IP地址

B.使用一个access-list命令匹配IP地址到,而不匹配其他IP

地址

C.使用一个access-list命令匹配Barney的子网中的所有IP地址，而不匹配其

他IP地址

D.仅匹配包的目标IP地址

正确答案：AC

2021思科认证考试题库精选8节第3节

802.1d定义了哪些端口状态?()

A.阻断

B.丢弃

C侦听

D学习

E.转发

F.替代

答案：ACDE

AEzonexamswitchisconfiguredwithallportsassignedtoVLAN2.In

addition,allportsareconfiguredasfull-duplexFastEthernet.Whatistheeffectof

addingswitchportstoanewVLANonthisswitch?

A.Theadditionswillcreatemorecollisionsdomains.

B.IPaddressutilizationwillbemoreefficient.

C.Morebandwidthwillberequiredthanwasneededpreviously.

D.Anadditionalbroadcastdomainwillbecreated.

E.Thepossibilitythatswitchingloopswilloccurwillincreasedramatically.

正确答案：D

解析:Explanation:

AVLANisagroupofhostswithacommonsetofrequirementsthat

communicateasiftheywereattachedtothesamewire,regardlessoftheir

physicallocation.AVLANhasthesameattributesasaphysicalLAN,butitallows

forendstationstobegroupedtogethereveniftheyarenotlocatedonthesame

LANsegment.

Networksthatusethecampus-wideorend-to-endVLANslogicallysegmenta

switchednetworkbasedonthefunctionsofanorganization,projectteams,or

applicationsratherthanonaphysicalorgeographicalbasis.Forexample,all

workstationsandserversusedbyaparticularworkgroupcanbeconnectedtothe

sameVLAN,regardlessoftheirphysicalnetworkconnectionsorinteractionwith

otherworkgroups.

Networkreconfigurationcanbedonethroughsoftwareinsteadofphysically

relocatingdevices.CiscorecommendstheuseoflocalorgeographicVLANsthat

segmentthenetworkbasedonIPsubnets.Eachwiringclosetswitchisonitsown

VLANorsubnetandtrafficbetweeneachswitchisroutedbytherouter.The

reasonsfortheDistributionLayer3switchandexamplesofalargernetwork

usingboththecampus-wideandlocalVLANmodelswillbediscussedlater.

AVLANcanbethoughtofasabroadcastdomainthatexistswithinadefinedset

ofswitches.PortsonaswitchcanbegroupedintoVLANsinordertolimit

unicast,multicast,andbroadcasttrafficflooding.Floodedtrafficoriginatingfrom

aparticularVLANisonlyfloodedoutportsbelongingtothatVLAN,including

trunkports,soaswitchthatconnectstoanotherswitchwillnormallyintroduce

anadditionalbroadcastdomain.

以下ACL将对路由器的流量产生何种影响（）

Access-!ist1deny192.168.19.1620.0.0.0

Access-!ist1permitany

A.它将允许所有源自的网络流量

B.它将拒绝源自主机62的流量

C.因为通配符掩码忽略了所有比特，所以对流量没有影响

D.permitany选项使deny选项失效

正确答案：B

下列静态路由配置正确的是0

A.iprouteserial0/0

B.iproute/24

C.iproute

D.iproute

正确答案：D

Afterloggingintoarouterandtypinginafewshowcommands,youpress

theuparrowkey.Whatwillthisdo?

A.Itwillrecallthepreviouscommandline

B.Itwillmovethecursoronelineup

C.Itwillredisplaythecurrentcommandline

D.Itwillcapitalizethecommandline

E.Noneoftheabove

正确答案：A

解析:Explanation:

Theuparrowkeyisusedtorecallthepreviouscommandlineentry.The

commandsthatwereenteredpreviouslycanbedisplayedbyrepeatedlypressing

theuparrowkey,orbyenteringthe"showhistory"command.

2021思科认证考试题库精选8节第4节

Usingasubnetmaskof24,whichoftheIPaddressesbelow

canyouassigntothehostsonthissubnet?(Selectallthatapply)

A.3

B.59

C.3

D.6

E.7

F.92

正确答案：CDE

C,D,E解析：Explanation:

Sincethesubnetmaskis24,thenumberofnetworkhoststhatis

availableis30.Everynetworkboundarywillbeamultipleof32.Thismeansthat

everysubnetwillbeamultiple(0,32,64,96,128,160,192,224)andthe

broadcastaddressforeachofthesesubnetswillbeonelessthisnumber(31,63,

95,127,159,191,223).

Therefore,anyIPaddressthatdoesnotendinoneofthesenumberswillbea

validhostIPaddress.

C.ValidHostinsubnetwork2(4to5)

D.ValidHostinsubnetwork1(2to3)

E.ValidHostinsubnetwork2(4to5)

IncorrectAnswers:

A.Thiswillbethebroadcastaddressforthe2/27network.

B.Thiswillbethebroadcastaddressforthe28/27network

F.Thiswillbethenetworkaddressforthe92/27network.

路由表中，某条路由的"路由代码为D”,则表明该路由为()

A.直连路由

B.静态路由

C.IGRP路由

D.EIGRP路由

正确答案：D

下列选项不属于分组交换技术的广域网通信协议有()。

A.X.25

B.帧中继

C.ATM

D.PSTN

正确答案：D

Whichtypeofcableshouldbeusedtomakeaconnectionbetweenthe

Fa0/0portonarouterandtheFa0/0portswitch?

A.Rollovercable

B.Consolecable

C.Crossovercable

D.Straight-throughcable

E.Serialcable

正确答案：D

解析：Explanation:Straight-

throughcablesareusedtoconnecthosttoswitch(orhub)androutertoswitch(orhub).

Youhavejustpurchasedabrandnewrouterandwishtohavetherouter

promptyouthroughtheinitialconfigurationcommands.Whichroutermode

doesthisdescribe?

A.ROMMonitormode

B.SETUPmode

C.Autoflashmode

D.RXBOOTmode

E.Noneoftheabove

正确答案：B

解析:Explanation:

Setupmodeisaconvenientmodethatwalksyouthroughthesetupprocedure

bypromptingyouwithspecificquestionsandoptionsonebyone.

2021思科认证考试题库精选8节第5节

EzonexamhasaClassCnetworkandyouneedtensubnets.Youwishtohave

asmanyaddressesavailableforhostsaspossible.Whichoneofthefollowing

subnetmasksshouldyouuse?

A.92

B.24

C.40

D.48

E.Noneoftheabove

正确答案：c

解析:Explanation:Usingthe2n-

2formula,wewillneedtouse4bitsforsubnetting,asthiswillprovidefor24-

2=14subnets.Thesubnetmaskfor4bitsisthen40.IncorrectAnswers:A.Th

iswillgiveusonly2bitsforthenetworkmask,whichwillprovideonly2networks.B.Thiswill

giveus3bitsforthenetworkmask,whichw川provideforonly6networks.D.Thisw川use5bi

tsforthenetworkmask,providing30networks.However,itwillprovideforonlyfor6hosta

ddressesineachnetwork.soCisabetterchoice.

什么是路由环路()

A.数据包在路由器的两个环回接口之间来回传递

B.从目的地返回的路径与出发路径不同而形成"环路"的情况

C.数据包在一系列路由器间不断传输却始终无法到达其真正的目的地的情况

D.路由从一种路由协议到另一种路由协议的分布

正确答案：C

WhichLayer4protocolisusedforaTelnetconnectionbetweentwo

Ezonexamrouters?

A.IP

B.ICMP

C.DNS

D.TCP

E.UDP

F.RTP

正确答案：D

D解析：Explanation:

TCPisareliableconnection-orientedprotocol.TCPusesacknowledgments,

sequencing,andflowcontroltoensurereliability.TelnetusesTCPport23.

Youareexperiencingintermittentissuesrelatingtocongestionwithinthe

Ezonexamnetwork.WhatarethepossiblecausesofcongestiononthisLAN?

(Chooseallthatapply)

A.Abroadcastdomainwithtoomanyhosts.

B.Fullduplexoperation.

C.Broadcaststorms.

D.Multicasting.

E.NetworkSegmentation.

F.Lowbandwidth.

正确答案：ACF

A,C,F解析：Explanation:

ALANsegmentwithtoomanyhostscanmeanthattherearealargenumberof

stationscontendingforbandwidth.Itcanalsomeananincreaseinthenumberof

collisionsonthesegment,whichcancausefurthercongestionissues.

Broadcaststormsaretheresultofalargenumberofbroadcastssentoverthe

LAN.Becauseeachstationlistenstothesebroadcastmessages,congestioncan

occurquickly.Finally,lowbandwidthcansimplymeanthattheLANcannot

processalloftheLANtrafficthatisbeingsent.ThiscanmeanthatTCPsessions

areretransmitted,whichcanleadtoadditionalcongestion.

IncorrectAnswers:

B.Thiscanalleviatecongestion,asdatacanbesentandreceivedatthesame

time.Inaddition,collisionsarenotpossibleinafullduplexLAN.

D.Multicastingcanactuallyalleviatecongestionissues,assinglestreamsof

informationcanreachmultiplehostsatthesametime,insteadofusingaseries

ofpointtopoint

connections.

E.SegmentationbreaksupalargeLANintomultiple,smallerLANS.Thiswill

meanfewerhostsperbroadcastdomain.

在路由器上，可以使用的命令有：0

A.ping

B.showinterfaces

C.showiproute

D.ipconfig

E.wincfg

正确答案：ABC

2021思科认证考试题库精选8节第6节

关于RIPV1和RIPV2,RIPV1报文支持子网掩码，RIPV2不支持子网掩码。

此题为判断题(对，错)。

正确答案：x

你使用命令copyrunning-configstartup-config保存路由器的配置，并重启路由

器，但路由器启动后没有任何运行配置。请问可能出现了什么问题?()

A.启动路由器时使用的命令不对

B.NVRAM受损

G配置寄存器的设置不正确

D.新升级到的IOS与路由器硬件不兼容

E.保存的配置与硬件不兼容

答案：C

对于以下ACL语句描述正确的是()

RI(config)#ipaccess-liststandardTELNET

RI(config-stdmacl)#permit192.168.4.20.0.0.0

R1#1ineytv04

RI(config-1ine)#access-classTELNETin

A.只允许的数据流穿过RI

B.只允许192,168.4.2对RI进行TELNET

C.只允许对R1进行TELNET并拒绝其它流量

D.只允许/24网段的数据流穿过R1

正确答案：B

下面关于地址转换，叙述正确的是0。

A.NAT技术不可以有效的隐藏内部局域网中的主机，但却是一种有效的网络

安全保护技术

B.一个局域网内部有很多主机，可是不能保证每台主机都拥有合法的公网IP

地址，为了达到所有的内部主机都可以连接Internet网络的目的,可以使用地址转

换

C.地址转换是在IP地址日益短缺的情况下提出的

D.NAT可以按照用户的需要,在局域网内部提供给外部FTP.WWW.Telnet

正确答案：BCD

Youhavejustpurchasedabrandnewrouterandwishtohavetherouter

promptyouthroughtheinitialconfigurationcommands.Whichroutermode

doesthisdescribe?

A.ROMMonitormode

B.SETUPmode

C.Autoflashmode

D.RXBOOTmode

E.Noneoftheabove

正确答案：B

解析:Explanation:

Setupmodeisaconvenientmodethatwalksyouthroughthesetupprocedure

bypromptingyouwithspecificquestionsandoptionsonebyone.

2021思科认证考试题库精选8节第7节

AfterworkingallnightandsuccessfullyconfiguringaCiscorouterforthe

Ezonexamnetworkyousaveyourchangesonthestartupconfig,rebootthe

router,andgooutforacigarette.Whenyoureturn,noneofyourchangesare

activeandtherouterbootstotheinitialconfigurationmode!Whichofthe

choicesbelowindicatesthesourceofyourproblem?

A.HardwarefailureinNVRAMpreventstherouterfromloadingtheconfig

B.Startup-configinflashiscorruptandcannotbeanalyzed

C-Routerconfiguration-registersettobypassstartupconfiguration

D.Startup-configinNVRAMiscorruptandcannotbeanalyzed

E.Noneoftheabove

正确答案：C

解析:Explanation:

Thedefaultconfiguration-registersettingof0x2102loadstheIOSfromflashand

theconfigurationfromNVRAM.

However,forpasswordrecovery,youcansettheregisterto0x2142andthe

startup-configfileinNVRAMwillbebypassed.Theproblemdescribedhereis

thattheconfigregisterwasnotchangedbackto0x2102beforetherouterwas

rebooted,sotheactiveconfigurationisbypassed.Simplysettingtheconfig

registerbackto0x2102willfixthisproblem.

IncorrectAnswers:

A,B,D.Allofthesedescribehardwareorsoftwareerrors.Intheeventthatthisis

theproblem,errorswillbegeneratedandtherouterwillfailtobootproperly.In

thesecases,therouterwillnotreturntotheinitialstartupconfiguration.

Whichthreeoftheprotocolsbelowbelongtotheapplicationlayer?(Select

threeanswerchoices)

A.ARP

B.HTTPS

C.SMTP

D.CDP

E.TFTP

F.ICMP

正确答案：BCE

B,C,E解析：Explanation:

TheapplicationlayeristhehighestOSIlayer,andprotocolsatthislayerareend­

useroriented.HTTPSsopeoplecangetinformationontheinternet,SMTPso

peoplecanmanagenetworks,andTFTPsopeoplecandownloadfiles.

IncorrectAnswers:

A,D,F.ARP,CDP,ICMPareprotocolsthatequipmentlikeroutersandswitches

usetocommunicatewiththemselves,andbelongtolowerlevelsonthemodel.

下列有关标准ACL和扩展AC