Tải bản đầy đủ - 0 (trang)
Appendix A. Answers to Review Questions

Appendix A. Answers to Review Questions

Tải bản đầy đủ - 0trang

Chapter1

1. InwhichlayersoftheOSImodeldoescontentnetworkingreside?



Answer:



ContentnetworkingdevicestechnicallyworkatLayers17,buttruecontent

networkingservicescanbeconsideredtoresideinLayers57oftheOSImodel.



2. Whatarethefourmainpurposesandgoalsofcontentnetworking?



Thefourmainpurposesandgoalsofcontentnetworkingareto:



-Performscalabilityandavailabilityservicesfor

applications.



Answer:



-Increaseavailablenetworkbandwidthand

decreaseapplicationresponsetimes.

-Providecustomizationandprioritizationofcontent

withinyournetwork.

-Enablesecurity,auditing,andmanagementofa

network.



3.



Answer:



Estimatehowmanyserversarerequiredtoprovide"fourninesofavailability"for

anapplicationknowntofail11.5percentofthetime?



Fiveserversarerequiredfortheapplicationtoachieve"fourninesof

availability":

1(0.115)5=0.99998=99.99%



4. Whatisthedifferencebetweenapplicationscalabilityandavailability?



Answer:



Applicationavailabilityrequiresreplicationtoensuredatarecovery,whereas

scalabilitysimplyincreasesthecapacityofasystem.



5. Howarebandwidthandresponsetimesreducedinacontentnetwork?



Answer:



Bandwidthandresponsetimesarereducedbyplacingcontentincloserproximity

torequestingclients.



6. WhatisthemaindifferencebetweenanICDNandanECDN?



AnICDNisownedandoperatedbyathird-partyproviderandoftenrequires

content-basedbillingsoftwaretotrackandchargeforcustomerbandwidthand

Answer:

contentusage.AnECDNisoftenowned,operated,andusedbythesame

organization,andthereforenousagebillingisrequired.



7. Namefourscenariosinwhichcontentcanbeswitched.



Answer:



Contentcanbeswitchedinthefollowingfourways:SLB,GlobalSLB,FWLB,and

VPNloadbalancing.



8. NamefoursolutionsthatCiscoACNScanprovide.



CiscoACNScanprovidethefollowingfoursolutions:point-of-salevideosand

Answer: Webkiosks,softwareandfiledistribution,e-learning,andcorporate

communications.



Chapter2

1.



Howmanywirepairsdoes100BASE-TuseofaUTPcoppercable?Howmany

does1000BASE-Tuse?



The100BASE-Tstandardusestwopairs(fourwiresintotal),onepairfor

transmittingandanotherforreceiving.The1000BASE-Tstandardusesallfour

Answer:

pairs(eightwiresintotal)oftheUTPcable.Usingechocancellation,eachpairis

capableoftransmittingandreceivingsimultaneously.



2.



Whatarethephysicaldifferencesbetweenstepandgradedindexmultimode

fiber?



Stepindexmultimodefiberhasthesamephysicalfiberpropertiesthroughout

thecore,whichresultsinasuddenreflective"step"intothefibercladding.In

Answer: contrast,variationsareimposedinthecompositionofgradedindexglassinthe

core,whichresultsinagradualincreaseinrefractiontowardthecenterofthe

core.



3.



For100BASE-FX,whyisNRZ-Isignalingusedwith4B/5Bencodingandnotjust

straightNRZ?



InTable2-3,quiteafewofthe5-bitcodeshavemoreonesthanzeros.The

Answer: reasonthat100BASE-FXusesNRZ-Iwith4B/5Bisthatmoretransitionsare

performedduringlongstringsofonesusingNRZ-IthanwithstraightNRZ.



4. WhaterrorcheckingisperformedwithIP,UDP,andTCP?



IPchecksforerrorsintheIPpacketonly.UDPandTCPcheckforerrorsinthe

Answer: UDPheaderandsegmentpayload,butonlyTCPretransmitserroneous

segments.



5. WhatisthepurposeoftheTCPthree-wayhandshake?



Answer:



TheTCPthree-wayhandshakeisusedtosynchronizeTCPsequencenumbers

andexchangeTCPoptionsbetweenTCPdevices.



6. HowispacketlossdetectedbyTCPsenders?



Outstandingsegmentsaredetectedbythesenderwitheitheratimeoutorby

Answer: receivingduplicateACKsfromthereceiver.



7.



WhyisTCPbandwidthlimitedoversatellitelinks?HowcanTCPbandwidthover

satellitebeaccelerated?



TheTCPwindowsizelimitsbandwidthoversatelliteconnectionsduetohigh

Answer: latency.UseofmultipleTCPconnectionsorthewindowscalingoption(WSopt)or

botharewaystoacceleratetheTCPbandwidthoversatellitelinks.



8. WhatisthelowestlevelofcontentawarenessinTCP/IP?



Answer:



TheTCPurgentpointeristhelowestlevelofcontentawarenessoftheTCP/IP

protocolsuite.



Chapter3

1. HowareMACaddresstablesbuiltinLayer2switches?



Answer:



Layer2switchesbuildMACaddresstablesbyinspectingARPtrafficflowing

acrosstheswitch.



2. DoLayer3switchesmaintainanARPcacheoraMACaddresstable?



Layer3switchesmaintainbothanARPcacheandaMACaddressforwarding

Answer: table.TheMACforwardingtableisusedtoforwardframesbetweenportswithin

asingleVLAN,andtheARPcacheisusedtorouteframesbetweenVLANs.



3. WhatisthepurposeofVTP?



VTPsavestimeconfiguringVLANsandsavesNVRAMspaceinlargenetwork

environments.ThenetworkadministratorneedsonlytoaddVLANstotheVTP

Answer:

serverbeforeassigningVLANstoswitchportsacrosstheentirenetwork.VTPis

alsousedtogiveVLANshuman-readablenames.



4.



Whatisthedifferencebetweendistance-vectorandlinks-statedynamicrouting

protocols?



Distance-vectoralgorithmssendperiodicroutingupdatesandusehopcount

metrics.Link-statealgorithmssendtriggeredupdateswhenchangesoccurand

Answer:

usemetricsbasedonthestateofthelinks(thatis,basedonthebandwidth,

delay,reliability,load,andMTUofthelink).



5. WhatisaRIB?GiveafewexamplesofprotocolsthatuseRIBs.



Theroutinginformationbasestoresroutinginformationlearnedbylink-stateand

Answer: hybrid-dynamicroutingprotocols.ThebestRIBroutesareinstalledinthemain

routingtable.OSPF,EIGRP,andBGProutingprotocolsmaintaintheirownRIBs.



6. WhatisaFIB?GiveafewexamplesofswitchingpathsthatuseFIBs.



Aforwardinginformationbaseisefficientdatastructurecontainingforwarding

informationusedbyrouterstobypassslow(er)routingtablesandARPcache



Answer: lookups.ExamplesofswitchingpathsthatuseRIBsarefastandCEFswitching.

ProcessswitchingdoesnotuseaRIB.



7.



WhatformofNATdocontentswitchesusetoloadbalancingrequestsacross

serverfarms?



Answer: DestinationNATisusedbycontentswitchestoperformserverloadbalancing.







Chapter4

1. WhatisthedifferencebetweenstatefulandstatelessACLs?



StatefulACLstracktransportstateinformation,suchasIPaddresses,TCP/UDP

Answer: ports,TCPsequencenumbers,andTCPflags.StatefulACLsdonottrackany

transportinformation.



2. HowdostatefulACLstracktransportstateinformation?



BasicACLstracktransportstatesimplybycheckingtoseeiftheACKorRSTTCP

flagsaresetintheTCPheader.IPsessionfilterscreatetemporaryACLentries

Answer: forreturntraffic.CBACandPIXfirewallsstoretransportstateinformationfor

eachconnectioninastatetable.ThetableincludesIPaddresses,TCP/UDPports,

TCPsequencenumbers,andTCPflags.



3. HowcanyouapproximateUDPconnections?



YoucanapproximateUDPconnectionsbytrackingpacketswiththesamesource

Answer: anddestinationIPaddressesandportsthattransitthefirewalloverthesame

timeframe.



4. Howcanyouachievesupervisorredundancy?



Answer:



Supervisorredundancyisachievedbyinstallingtwosupervisorsinasingle

chassis,orbyusingtwochassiswithasinglesupervisorinstalledineach.



5. Howcanyouachieveswitchfabricredundancy?



Foractivebackplanes,twochassisarerequiredforredundancy.Forpassive

backplanes(thatis,SFMsorintegratedswitchfabrics),eithertwomodulesina

Answer:

singlechassisortwochassiswithasinglemoduleeacharerequiredfor

redundancy.



6. Whatisonebenefitofsandwichingpublicserversbetweentwofirewalls?



Bothsingleanddualfirewallconfigurationssecureinternalresourcesfromthe

Answer: publicresources.However,serversandwichingenablesfirewallsofdifferent



vendorstosecureinternalresources.



7. Whatcontentnetworkingsolutionsdoremotebranchusersbenefitfrom?



Answer:



Remoteofficeusersbenefitfromcontentedgedelivery,distribution,androuting

inordertoplacecontentclosertotheclient.



Chapter5

1. WhatisthedifferencebetweentheISMandSSMmulticastmodels?



WiththeISMmodel,theroutersinthenetworkmaintainsourceinformation.

However,withSSMthereceiversareresponsibleforspecifyingthedesired

Answer: source.ThereceiverapplicationobtainsknowledgeofthesourceunicastIP

addressorURLthroughmethodsexternaltothemulticastprotocol,suchasthe

userselectingthesourcefromalistofavailablesourcessuppliedbyawebpage.



2.



HowmanypossiblegloballyscopedmulticastaddressesareavailableforISM?

ForSSM?



TheIANAallocatesmulticastaddresseswithintherange232.0.0.0

232.255.255.255toSSM.

Fortheentiremulticastrange224.0.0.0239.255.255.255,thereare16*224=

16*16,777,216=268,435,456possibleaddressesavailable.Therefore,to

calculatetheavailableaddressesforISMapplications,subtractthelocallyscoped

8

Answer: addresses(thatis,2 =256addressesfortherange224.0.1.0224.0.1.255)

andtheSSMaddressesfromthisnumber.Theresultis268,435,45616,777,216

256=251,657,984.Youhavetodividethisnumberby32becauseofthe32-to1mappingofaddressestoEthernetMACaddresses.Theresultis251,657,984/

32=7,864,312possibleaddressesavailableforISMand16,777,216/32=

524,288forSSM.Becausemulticastapplicationsrandomlyassignmulticast

addresses,thechancesofhavingframeswithduplicateMACaddressesonan

EthernetLANareverylow.



3. Whatisthedifferencebetweensourceandshareddistributiontrees?



Withsourcetrees,thesourceofthemulticaststreamisattherootofthetree,

providingtheshortestpossiblepathbetweenthesourceandreceiversofthe

Answer:

content.RendezvousPointsaretherootofsharedtreesandoftencausethe

multicaststreamtotakeasuboptimalpathtothereceivers.



4. Howdoesdense-modemulticastdifferfromsparse-modemulticast?



Dense-moderoutersperiodicallyfloodthemulticaststreamtotheentire

network,eventolast-hoproutersthatdonothaveactivereceiversforthe

Answer:

group.Sparse-moderouterssendthemulticaststreamonlytolast-hoprouters

thatcontainmulticastreceiversforthestream.



5.



Answer:



Howdomulticastroutersroutemulticastpacketsdownstream?



Multicastroutersusereversepathforwarding(RPF)toforwardframestolasthoprouters.



6. Howdomulticastroutersroutemulticastpacketsupstream?



ForforwardingPIMJoinmessagesupthedistribution,insteadofcheckingtosee

ifthesourceofthepacket(thelast-hoprouter,inthiscase)isreachablefrom

theRPinterfaceusingRPF,therouterchecksitsoutgoinginterface(OIF)list.If

Answer: therouterreceivesthepacketfromaninterfaceintheOIFlist,thentherouter

forwardsthepacketoutitsRPFinterface.

Forforwardingmulticaststreamdataupthedistributiontree,youneedto

configureBidir-PIM.



7. WhatisthedifferencebetweenAuto-RPandBSR?



Auto-RPdistributestheRPcandidateinformationusingdense-modemulticast,

forcingyoutoenablePIMsparse-densemodeonallAuto-RProuters.BSRusesa

Answer:

hop-by-hopmethod,allowingyoutoconfigureonlyPIMsparsemodeonallBSR

routers.



8. WhatarethedifferencesbetweenAuto-RP,BSR,andAnycastRP?



TheAuto-RPandBSRprotocolsdonotallowyoutoconfigureload-balancingof

Answer: streamswithinthesamegroupbetweenmultipleactiveRPs.AnycastRPallows

per-grouploadbalancing.



9. WhatarethedifferencesbetweenCGMPandIGMPsnooping?



BothCGMPandIGMPsnoopingprovideyouwiththeabilitytorestrictmulticast

trafficinaLayer2switchednetworktoonlythoseportswithactivereceivers

Answer: attached.However,youmustconfigureCGMPontheroutertosignaltothe

switchwhichportstoforwardthetrafficto.YoudonotneedtoconfigureIGMP

snoopingontherouterbecausetheswitchinspectstheIGMPmessagesdirectly.



Chapter6

1. WhattoolscanyouusetomarkIPprecedenceandDSCP?



YoucanmarkDSCPwithclass-basedpacketmarkingonly.YoucanmarktheIP

PrecedenceofapacketusingPolicy-BasedRouting,QoSPolicyPropagationvia

Answer:

BorderGatewayProtocol,CommittedAccessRate/Class-BasedPolicing,Network

BasedApplicationRecognition,andClass-BasedPacketMarking.



2.



Ifarouterhas100,000concurrentconnectionsonaverage,approximatelyhow

muchmemorydoesNBARusetostoreinformationforthoseconnections?



Answer: NBARusesapproximately15MBofmemory.



3. WhyisWFQnotscalabletohigh-speedlinks?



BecauseWFQusesasinglequeueperflow,thenumberofrequiredqueues

Answer: wouldgrowtoohighforhigh-speedlinks,andpotentiallyfloodtherouter's

memory.



4. WhatisthedifferencebetweenstandardWFQandCBWFQ?



StandardWFQautomaticallyclassifiestrafficintoflows,andyourequireonlya

singleinterfaceconfigurationcommand(fair-queue).Incontrast,CBWFQallows

Answer: youtoconfigureclassesoftrafficandallocatebandwidthtotheclassesthrough

theMQC.Furthermore,becauseeachflowinstandardWFQistrackedin

memory,WFQisnotasscalableasCBWFQ.



5.



HowmanyegressqueuesdoCatalyst29xx/35xx/37xx/4xxxseriesswitches

have?WhataboutCatalyst6500seriesswitches?



Catalyst29xx/35xx/37xx/4xxxserieshavefouregressqueues.Todeterminethe

Answer: numberofegressqueuesonyourCatalyst6500seriesswitches,usetheshow

portcapabilitiescommand.



6. Whatisthedifferencebetweentrafficshapingandpolicing?



Trafficpolicingdropspacketswhenthetokenbucketsarefull,whereasshaping



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Appendix A. Answers to Review Questions

Tải bản đầy đủ ngay(0 tr)

×