General Network Engineer Interview Questions _ Part 5_5 General Knowledge Questions _ Syed Jahanzaib Personnel Blog to Share Knowledge !

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February22,2010

GeneralNetworkEngineerInterviewQuestions/Part5/5GeneralKnowledgeQuestions

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GeneralNetworkEngineerInterviewQuestions

GeneralKnowledgeQuestions

~SyedJahanzaib~

DescribetheOSImodel.(pronouncedasseparateletters)ShortforOpenSystemInterconnection,anISOstandardforworldwidecommunicationsthatdefinesanetworkingframeworkforimplementingprotocolsinsevenlayers.Controlispassedfromonelayertothenext,startingattheapplicationlayerinonestation,proceedingtothebottomlayer,overthechanneltothenextstationandbackupthehierarchy.

Atonetime,mostvendorsagreedtosupportOSIinoneformoranother,butOSIwastoo



Atonetime,mostvendorsagreedtosupportOSIinoneformoranother,butOSIwastoolooselydefinedandproprietarystandardsweretooentrenched.ExceptfortheOSIcompliantX.400andX.500emailanddirectorystandards,whicharewidelyused,whatwasoncethoughttobecometheuniversalcommunicationsstandardnowservesastheteachingmodelforallotherprotocols.

MostofthefunctionalityintheOSImodelexistsinallcommunicationssystems,althoughtwoorthreeOSIlayersmaybeincorporatedintoone.

OSIisalsoreferredtoastheOSIReferenceModelorjusttheOSIModel.OpenSystemInterconnectionanISOstandardforworldwidecommunicationsthatdefinesanetworkingframeworkforimplementingprotocolsinsevenlayers.Thesevenlayers&Functionsare:

Application(Layer7)Thislayersupportsapplicationandenduserprocesses.Communicationpartnersareidentified,qualityofserviceisidentified,userauthenticationandprivacyareconsidered,andanyconstraintsondatasyntaxareidentified.Everythingatthislayerisapplicationspecific.Thislayerprovidesapplicationservicesforfiletransfers,email,andothernetworksoftwareservices.TelnetandFTPareapplicationsthatexistentirelyintheapplicationlevel.Tieredapplicationarchitecturesarepartofthislayer.

Presentation(Layer6)Thislayerprovidesindependencefromdifferencesindatarepresentation(e.g.,encryption)bytranslatingfromapplicationtonetworkformat,andviceversa.Thepresentationlayerworkstotransformdataintotheformthattheapplicationlayercanaccept.Thislayerformatsandencryptsdatatobesentacrossanetwork,providingfreedomfromcompatibilityproblems.Itissometimescalledthesyntaxlayer.

Session(Layer5)Thislayerestablishes,managesandterminatesconnectionsbetweenapplications.Thesessionlayersetsup,coordinates,andterminatesconversations,exchanges,anddialoguesbetweentheapplicationsateachend.Itdealswithsessionandconnectioncoordination.

Transport(Layer4)Thislayerprovidestransparenttransferofdatabetweenendsystems,orhosts,andisresponsibleforendtoenderrorrecoveryandflowcontrol.Itensurescompletedatatransfer.

Network(Layer3)Thislayerprovidesswitchingandroutingtechnologies,creatinglogicalpaths,knownasvirtualcircuits,fortransmittingdatafromnodetonode.Routingandforwardingarefunctionsofthislayer,aswellasaddressing,internetworking,errorhandling,congestioncontrolandpacketsequencing.

DataLink(Layer2)Atthislayer,datapacketsareencodedanddecodedintobits.Itfurnishestransmissionprotocolknowledgeandmanagementandhandleserrorsinthephysicallayer,flowcontrolandframesynchronization.Thedatalinklayerisdividedintotwosublayers:The



MediaAccessControl(MAC)layerandtheLogicalLinkControl(LLC)layer.TheMACsublayercontrolshowacomputeronthenetworkgainsaccesstothedataandpermissiontotransmitit.TheLLClayercontrolsframesynchronization,flowcontrolanderrorchecking.

Physical(Layer1)Thislayerconveysthebitstreamelectricalimpulse,lightorradiosignalthroughthenetworkattheelectricalandmechanicallevel.Itprovidesthehardwaremeansofsendingandreceivingdataonacarrier,includingdefiningcables,cardsandphysicalaspects.FastEthernet,RS232,andATMareprotocolswithphysicallayercomponents.

ApplicationLayersUsageExample:

7.ApplicationLayerNNTPSIPSSIDNSFTPGopherHTTPNFSNTPSMPPSMTPSNMPTelnet(more)

6.PresentationLayer:MIMEXDR

5.SessionLayer:NamedPipesNetBIOSSAP

4.TransportLayer:TCPUDPPPTPSCTPSSLTLS

3.NetworkLayer:IPICMPIPsecIGMPIPXAppleTalk

2.DataLinkLayerARP:CSLIPSLIPEthernetFramerelayITUTG.hnDLLL2TPPPP

1.PhysicalLayer:RS232V.35V.34I.430I.431T1E1POTSSONET/SDHOTNDSL802.11a/b/g/nPHYITUTG.hnPHY

Whatisthedifferencebetweenarepeater,bridge,router?RelatethistotheOSImodel

Bridges:

(sometimescalledTransparentbridges)workatOSImodelLayer2.Thismeanstheydontknowanythingaboutprotocols,butjustforwarddatadependingonthedestinationaddressinthedatapacket.ThisaddressisnottheIPaddress,buttheMAC(MediaAccessControl)addressthatisuniquetoeachnetworkadaptercard.Bridgesareveryusefulforjoiningnetworksmadeofdifferentmediatypestogetherintolargernetworks,andkeepingnetworksegmentsfreeofdatathatdoesntbelonginaparticularsegment.

Switches:

SwitchesarethesamethingasBridges,butusuallyhavemultipleportswiththesameflavorconnection(Example:10/100/10000BaseT).

Switchescanbeusedinheavilyloadednetworkstoisolatedataflowandimproveperformance.Inaswitch,databetweentwolightlyusedcomputerswillbeisolatedfromdataintendedforaheavilyusedserver,forexample.Orintheoppositecase,inautosensingswitchesthatallowmixingof10and100Mbpsconnections,theslower10Mbpstransferwontslowdownthefaster100Mbpsflow.

Repeater:



Repeater:Forwardseveryframeitreceivesitisagenerator,notanamplifier(i.eitremovesnoise&regeneratessignal)BidirectionalinnatureUsefulinincreasingethernetsize/lengthMaximumof5RepeatersinanEthernet

RoutersLinksdissimilarn/wsnottransparenttoendstationsactsonanetworklayerframeisolatesLANtosubnetstomanage&controltraffic

vDescribeanEthernetswitchandwhereitfitsintotheOSImodel.

AswitchisahardwaredevicethatworksatLayer2oftheOSImodeldatalink.ThedatalinklayeriswheretheEthernetprotocolworks.

AswitchswitchesEthernetframesbykeepingatableofwhatMACaddresseshavebeenseenonwhatswitchport.Theswitchusesthistabletodeterminewheretosendallfutureframesthatitreceives.InCiscoterminology,thistableiscalledtheCAMtable(contentaddressablememory).Ingeneral,thepropertermforthistableisthebridgeforwardingtable.IfaswitchreceivesaframewithadestinationMACaddressthatitdoesnothaveinitstable,itfloodsthatframetoallswitchports.Whenitreceivesaresponse,itputsthatMACaddressinthetablesothatitwonthavetofloodnexttime.

Aswitchisahighspeedmultiportbridge.Thisiswhybridgesarenolongerneededormanufactured.Switchesdowhatbridgesdidfasterandcheaper.Mostrouterscanalsofunctionasbridges.

Youmightbeaskinghowahubfitsintothismixofdevices.Ahubisamultiportrepeater.Inotherwords,anythingthatcomesinoneportofahubisduplicatedandsentoutallotherportsofthehubthathavedevicesattached.Thereisnointelligencetohowahubfunctions.Aswitchisavastimprovementoverahubintermsofintelligence,formanyreasons.Themostimportantofthosereasonsishowthebridgeforwardingtableworks.Intelligent(smart)switcheshavemadehubsobsoletebecausetheycandomoreatthesamecostofadumbhub.Forthisreason,hubsarerarelyusedorsoldanylonger.

vWhatisaVLAN?WhatisanELAN?Whatisthedifference?

ShortforvirtualLAN,anetworkofcomputersthatbehaveasiftheyareconnectedtothesamewireeventhoughtheymayactuallybephysicallylocatedondifferentsegmentsofaLAN.VLANsareconfiguredthroughsoftwareratherthanhardware,whichmakesthemextremelyflexible.OneofthebiggestadvantagesofVLANsisthatwhenacomputerisphysicallymovedtoanotherlocation,itcanstayonthesameVLANwithoutanyhardwarereconfiguration.

AVLANisalogicallocalareanetwork(orLAN)thatextendsbeyondasingletraditionalLANtoagroupofLANsegments,givenspecificconfigurations.BecauseaVLANisalogicalentity,itscreationandconfigurationisdonecompletelyinsoftware.



VLANVirtualLocalAreaNetwork

ELANEmulatedLocalAreaNetwork

Differencebetweenthesetwoareasfollows:

WithoutgoingintothemechanicsofELANsandhowtheyareconfigured,anELAN(EmulatedLAN)connectsVLANsoveraWAN.

AVLAN(VirtualLAN)isagroupingofportsonswitcheswhichisconsideredasonebroadcastdomain.AlltheportsonaVLANactasiftheywereallonthesamewire.Therefore,broadcastsarepropagatedacrossaVLAN,andanythingcommunicationoutsidethatVLANmustberoutedorbridged.

TheELANisamechanismusedtolinkVLANsacrossawideareanetwork.ATMisagoodcandidateforELANs.WithELANs,youcouldhave2VLANsatdifferentsiteswhicharelinkedtogetherviaanELAN.TheELANlinksthetwoVLANs

Together,formingonebigbroadcastdomain.TheadvantageofELANsoverstraightbridgingisthatmembershipintoELANsisdynamic,andthatmultipleELANscanbehandledbyonesingleWANlink.

vDescribeEthernetpacketcontents:min./max.size,header.Ethernetframeconsistsof:7bytesPreamble1byteSOFDelimiter6bytesDA6bytesSA2bytesType\Length461500bytesData\802.2Header+Data4bytesFCS

Minamountofbytesis72.Ethernetframeminimalsizeis64=72bytesofframe7bytesofpreamble1byteofSOF.

Theethernetframesizeupperlimitof1500bytesgoesuptothehistoryofDIXEthernetphysicallimitofmemorysizeusedinNICsbecauseofitscost.Actuallythereisnostrictrequirementsbyusedalgorythmsorstandarts.

Lowerlimitofframesizehasthefollowingreasons:1.Tomaketransmissionerrordetectionmoreeasysmallersizeofbinarysequenceleadstolowerreliabilityoferrordetection.

2.Themostimportantreason:Ifframesizeislessthan64bytes(512bits),hostmayfinishtransmissionbeforereceivingnoisesignalandcanthinkthatframetransmittedsuccessfully,whileanotherhostsentcollisionnotification.For10Mbpsrateminframesizeshouldbeatleast500bitsthatstheonlyguaranteethatcollisioncanbedetectedanywhereinthecable.Forreliabilityminsizewasincreasedupto512



(powerof2)andbecame512bits=64bytes.theminsizewastomakesurethatitcontainsenoughethernetheaders.themaxsizealsohassomethingtodowiththedatawrittenintheheaders.

vDescribeTCP/IPanditsprotocols.TheTCP/IPsuiteofprotocolsisthesetofprotocolsusedtocommunicateacrosstheinternet.Itisalsowidelyusedonmanyorganizationalnetworksduetoitsflexibilityandwidearrayoffunctionalityprovided.MicrosoftwhohadoriginallydevelopedtheirownsetofprotocolsnowismorewidelyusingTCP/IP,atfirstfortransportandnowtosupportotherservices.

IPInternetProtocol.ExceptforARPandRARPallprotocolsdatapacketswillbepackagedintoanIPdatapacket.IPprovidesthemechanismtousesoftwaretoaddressandmanagedatapacketsbeingsenttocomputers.

TCP/IPisatwolayerprogram.Thehigherlayer,TransmissionControlProtocol,managestheassemblingofamessageorfileintosmallerpacketsthataretransmittedovertheInternetandreceivedbyaTCPlayerthatreassemblesthepacketsintotheoriginalmessage.Thelowerlayer,InternetProtocol,handlestheaddresspartofeachpacketsothatitgetstotherightdestination.Eachgatewaycomputeronthenetworkchecksthisaddresstoseewheretoforwardthemessage.Eventhoughsomepacketsfromthesamemessagearerouteddifferentlythanothers,theyllbereassembledatthedestination.

TCPAreliableconnectionorientedprotocolusedtocontrolthemanagementofapplicationlevelservicesbetweencomputers.Itisusedfortransportbysomeapplications.UDPAnunreliableconnectionlessprotocolusedtocontrolthemanagementofapplicationlevelservicesbetweencomputers.Itisusedfortransportbysomeapplicationswhichmustprovidetheirownreliability.

ManyInternetusersarefamiliarwiththeevenhigherlayerapplicationprotocolsthatuseTCP/IPtogettotheInternet.TheseincludetheWorldWideWebsHypertextTransferProtocol(HTTP),theFileTransferProtocol(FTP),Telnet(Telnet)whichletsyoulogontoremotecomputers,andtheSimpleMailTransferProtocol(SMTP).TheseandotherprotocolsareoftenpackagedtogetherwithTCP/IPasasuite.

vDescribeATMandwhatareitscurrentadvantagesanddisadvantages.DescribeSONET

ATM(asynchronoustransfermode)isadedicatedconnectionswitchingtechnologythatorganizesdigitaldatainto53bytecellunitsandtransmitsthemoveraphysicalmediumusingdigitalsignaltechnology.Individually,acellisprocessedasynchronouslyrelativetootherrelatedcellsandisqueuedbeforebeingmultiplexedoverthetransmissionpath.

BecauseATMisdesignedtobeeasilyimplementedbyhardware(ratherthansoftware),fasterprocessingandswitchspeedsarepossible.Theprespecifiedbitratesareeither155.520Mbpsor622.080Mbps.SpeedsonATMnetworkscanreach10Gbps.AlongwithSynchronousOpticalNetwork(SONET)andseveralothertechnologies,ATMisakeycomponentofbroadbandISDN(BISDN).

ATMalsostandsforautomatedtellermachine,amachinethatbankcustomersusetomake



ATMalsostandsforautomatedtellermachine,amachinethatbankcustomersusetomaketransactionswithoutahumanteller.

AdvantagesandDisadvantagesofATM

ATMAdvantagesATMsupportsvoice,videoanddataallowingmultimediaandmixedservicesoverasinglenetwork.Highevolutionpotential,workswithexisting,legacytechnologiesProvidesthebestmultipleservicesupportSupportsdelayclosetothatofdedicatedservicesSupportsthebroadestrangeofburstiness,delaytoleranceandlossperformancethroughtheimplementationofmultipleQoSclassesProvidesthecapabilitytosupportbothconnectionorientedandconnectionlesstrafficusingAALsAbletouseallcommonphysicaltransmissionpathslikeSONET.Cablecanbetwistedpair,coaxialorfiberopticAbilitytoconnectLANtoWANLegacyLANemulationEfficientbandwidthusebystatisticalmultiplexingScalabilityHigheraggregatebandwidthHighspeedMbpsandpossiblyGbps

ATMdisadvantages

Flexibletoefficiencysexpense,atpresent,foranyoneapplicationitisusuallypossibletofindamoreoptimizedtechnologyCost,althoughitwilldecreasewithtimeNewcustomerpremiseshardwareandsoftwarearerequiredCompetitionfromothertechnologies100MbpsFDDI,100MbpsEthernetandfastEthernetPresentlytheapplicationsthatcanbenefitfromATMsuchasmultimediaarerareThewait,withallthepromiseofATMscapabilitiesmanydetailsarestillinthestandardsprocess

vWhatarethemaximumdistancesforCAT5cabling?

Agoodstandardansweris100meters(300feet)withpatchcords,90meters(270feet)withoutpatchcords.ThatgoesprettymuchforeverythinguptoandincludingCAT7/ClassFaUTP.

Maximumcablelenghforethernetdependsonwhatkindofethernetyouaretalkingabout!Herearesomedetailsonthemostpopularkindsofethernet.(UTP=unshieldedtwistedpair)GigabitEthernet(overcopper),1000baseT

Speed: 1000Mbps

MaxLen: 100Meters

Cable: UTP,RJ45connectorsFastEthernet,100baseT



Speed: 100Mbps

MaxLen: 100Meters

Cable: UTP,RJ45connectorsTwistedPairEthernet,10baseT

Speed: 10Mbps

MaxLen: 100Meters

Cable: UTP,RJ45connectorsThinEthernet,10base2

Speed: 10Mbps

MaxLen: 185Meters

Cable: RG58typecoax,50ohmimpedanceThickEthernet,10base5

Speed: 10Mbps

MaxLen: 500Meters

Cable: RG58typecoax,50ohmimpedance

vDescribeUDPandTCPandthedifferencesbetweenthetwo.

TCPAreliableconnectionorientedprotocolusedtocontrolthemanagementofapplicationlevelservicesbetweencomputers.Itisusedfortransportbysomeapplications.

UDPAnunreliableconnectionlessprotocolusedtocontrolthemanagementofapplicationlevelservicesbetweencomputers.Itisusedfortransportbysomeapplicationswhichmustprovidetheirownreliability.

vDescribewhatabroadcaststormis.

Astateinwhichamessagethathasbeenbroadcastacrossanetworkresultsinevenmoreresponses,andeachresponseresultsinstillmoreresponsesinasnowballeffect.Aseverebroadcaststormcanblockallothernetworktraffic,resultinginanetworkmeltdown.Broadcaststormscanusuallybepreventedbycarefullyconfiguringanetworktoblockillegalbroadcastmessages.

vDescribewhatarunt,agiant,andalatecollisionareandwhatcauseseachofthem.

Aruntisapacketthatfailstomeettheminimumsizestandard.Ussuallybelow64bytes.Occursasaresultofacollision.

Agiantisapacketthatexceedsthesizestandardforthemediumussuallygraterthen1518bytes.Causedbymalfunctioningequipmentonyournetwork.

Latecollisionsarepacketcollisionsthatoccurafterthewindow



Latecollisionsarepacketcollisionsthatoccurafterthewindowforanetworkcollisioncloses.

vHowdoyoudistinguishaDNSproblemfromanetworkproblem?

Ifyoureabletoping157.166.224.26butyouareNOTabletopingcnn.com,ThenyourehavingaDNSproblem.

[IfyouareNOTabletopingEITHER,thentherearenetworkproblemsandyouhaveNOproblemsifyouCANpingBOTH]

Youcanthenusenslookuptolocateanalternateinternalorexternaldnsserverthatcorrectlyresolvescnn.comtoitsipaddressandconfigureyourworkstationsNICforthisstaticdnsserveruntiltheproblemswiththeDHCPassignedDNSserverarefixed.OR

WhenuareabletopingthedefaultgatewayandthewebsiteaddressthereisnoprobleminthenetworkandDNS

WhenuareabletopingthethegatewayandtheWEBsiteIP,butnottheWEBsiteaddressthenitisaproblemwiththeDNS

Whenuarenotabletopinganythingitsnetworkproblem

vDescribetheprincipleofmultilayerswitching.MultilayerswitchingissimplythecombinationoftraditionalLayer2switchingwithLayer3routinginasingleproduct.Multilayerswitchingisnew,andthereisnoindustrystandardyetonnomenclature.Vendors,analysts,andeditorsdontagreeaboutthespecificmeaningoftermssuchasmultilayerswitch,Layer2router,Layer3switch,IPswitch,routingswitch,switchingrouter,andwirespeedrouter.ThetermmultilayerswitchseemstobethebestandmostwidelyuseddescriptionofthisclassofproductthatperformsbothLayer3routingandLayer2switchingfunctions.

MultilayerswitchingisusuallyimplementedthroughafasthardwaresuchasahigherdensityASICs(ApplicationSpecificIntegratedCircuits),whichallowrealtimeswitchingandforwardingwithwirespeedperformance,andatlowercostthantraditionalsoftwarebasedroutersbuiltaroundgeneralpurposeCPUs.

Thefollowingaresomebasicarchitectureapproachesforthemultiplayerswitches:

GenericCutThroughRouting:InthemultilayerswitchingarchitectureLayer3routingcalculationsaredoneonthefirstpacketinadataflow.FollowingpacketsbelongingtothesameflowareswitchedatLayer2alongthesameroute.Inotherwords,routecalculationandframeforwardingarehandledverydifferentlyhere.

ATMBasedCutThroughRouting:ThisisavariationofgenericcutthroughroutingwhichisbasedonATMcellsratherthanframes.ATMbasedcutthroughroutingoffersseveraladvantagessuchasimprovedsupport



ofLANemulationandmultivendorsupportintheformoftheMultiprotocolOverATM(MPOA)standard.ProductsreferredtoasIPswitchesandtagswitchesgenerallyfallintothiscategory.

Layer3LearningBridgingCInthisarchitecture,routingisnotprovided.Instead,itusesIPsnoopingtechniquestolearntheMAC/IPaddressrelationshipsofendstationsfromtrueroutersthatmustexistelsewhereinthenetwork.ThenitredirectstrafficawayfromtheroutersandswitchesitbasedonitsLayer2addresses.

WirespeedRouting:Wirespeedarchitecturerouteseverypacketindividually.ItisoftenreferredtoaspacketbypacketLayer3switching.UsingadvancedASICstoperformLayer3routinginhardware,itimplementsdynamicroutingprotocolssuchasOSPFandRIP.InadditiontobasicIProuting,itsupportsIPmulticastrouting,VLANsegregation,andmultipleprioritylevelstoassistinqualityofservice.

NetworkTroubleshooting

vExplainhowtraceroute,ping,andtcpdumpworkandwhattheyareusedfor?Traceroute;

Tracerouteworksbyincreasingthetimetolivevalueofeachsuccessivebatchofpacketssent.Thefirstthreepacketssenthaveatimetolive(TTL)valueofone(implyingthattheyarenotforwardedbythenextrouterandmakeonlyasinglehop).ThenextthreepacketshaveaTTLvalueof2,andsoon.Whenapacketpassesthroughahost,normallythehostdecrementstheTTLvaluebyone,andforwardsthepackettothenexthost.WhenapacketwithaTTLofonereachesahost,thehostdiscardsthepacketandsendsanICMPtimeexceeded(type11)packettothesender.Thetracerouteutilityusesthesereturningpacketstoproducealistofhoststhatthepacketshavetraversedenroutetothedestination.Thethreetimestampvaluesreturnedforeachhostalongthepatharethedelay(akalatency)valuestypicallyinmilliseconds(ms)foreachpacketinthebatch.Ifapacketdoesnotreturnwithintheexpectedtimeoutwindow,astar(asterisk)istraditionallyprinted.Traceroutemaynotlisttherealhosts.Itindicatesthatthefirsthostisatonehop,thesecondhostattwohops,etc.IPdoesnotguaranteethatallthepacketstakethesameroute.AlsonotethatifthehostathopnumberNdoesnotreply,thehopwillbeskippedintheoutput.

Ping:

ItworksbysendingICMPechorequestpacketstothetargethostandlisteningforICMPechoresponsereplies.Pingestimatestheroundtriptime,generallyinmilliseconds,andrecordsanypacketloss,andprintsastatisticalsummarywhenfinished.TCPDUMP:

tracerouteandpingworkontheICMPprotocolandareusedfornetworkconnectivitytesting.butTCPDUMPisdifferentitsaNETWORKPACKETANALYZER.tcpdumpuseslibpacp/winpcaptocapturedataandusesitextensiveprotocoldefinitionsbuildinsidetoanalyzethecapturedpackets.Itsmainlyusedtodebugtheprotocolofthecapturedpacketwhichinturnrevealsthenetworktrafficcharachterstics.



vWhatisametric?

Metricsisapropertyofarouteincomputernetworking,consistingofanyvalueusedbyroutingalgorithmstodeterminewhetheronerouteshouldperformbetterthananother(theroutewiththelowestmetricisthepreferredroute).Theroutingtablestoresonlythebestpossibleroutes,whilelinkstateortopologicaldatabasesmaystoreallotherinformationaswell.Forexample,RoutingInformationProtocoluseshopcount(numberofhops)todeterminethebestpossibleroute.

AMetriccaninclude:

measuringlinkutilisation(usingSNMP)numberofhops(hopcount)speedofthepathpacketloss(routercongestion/conditions)latency(delay)pathreliabilitypathbandwidththroughput[SNMPqueryrouters]loadMTU

vWhatisanetworkmanagementsystem?

ANetworkManagementSystem(NMS)isacombinationofhardwareandsoftwareusedtomonitorandadministeranetwork

Effectiveplanningforanetworkmanagementsystemrequiresthatanumberofnetworkmanagementtasksbefoldedinasinglesoftwaresolution.Thenetworkmanagementsystemshouldautomatetheprocessesofexpensemanagementauditing,assetlifecyclemanagement,inventorydeploymenttracking,costallocationandinvoiceprocessing.

vDescribehowSNMPworks.

Thesimplenetworkmanagementprotocol(SNMP)useformonitoringofnetworkattacheddevicesforanyconditionsthatwarrantadministrativeattention.ItisusetomanageIPnetworkdevicessuchasservers,routers,switchesetc.Administratorcanfindormanage



networkperformance,solveproblemorevenoptimizeitfurther.ItworksatTCP/IPApplicationlayer5(L5).

vDescribehowWEPworksanditsstrengthsandweaknesses

AsyouprobablyalreadyknowWiredEquivalentPrivacy(WEP)isusedbycompaniestosecuretheirwirelessconnectionsfromsniffingattacks.Youveprobablyalsoheardthatitsnotverysecure.Inthefirstpartofthis2partseriesIllexplaintheinnerworkingsofWEPandfollowitupnextmonthwithwhyitsinsecure.

DoineedWEPatall?

Anauthenticuser,BobuseshislaptoptocheckhisGmailaccounteveryday.HehasawirelesscardinhislaptopwhichautomaticallydetectshisISPswirelessaccesspoint(WAP)justacrossthestreet.OncehesconnectedtotheWAPhecangoaheadandcheckhisEmail.AliceisasneakyuserwhodoesntwanttopaytheISPforaccesstotheInternet.ShehoweverknowsthattheISPacrossthestreethasanaccesspointwhichanyonecanconnecttoandaccesstheInternet.SheplugsinherlaptopandissoondownloadingmusicfromtheInternet.WEPwasdesignedtoensurethatusersauthenticatethemselvesbeforeusingresources,toblockoutAlice,andallowBob.Letsseehowitdoesthis.

HowWEPworks

WEPusestheRC4algorithmtoencryptthepacketsofinformationastheyaresentoutfromtheaccesspointorwirelessnetworkcard.Assoonastheaccesspointreceivesthepacketssentbytheusersnetworkcarditdecryptsthem.

Eachbyteofdatawillbeencryptedusingadifferentpacketkey.Thisensuresthatifahackerdoesmanagetocrackthispacketkeytheonlyinformationthatisleakedisthatwhichiscontainedinthatpacket.

TheactualencryptionlogicinRC4isverysimple.TheplaintextisXORedwithaninfinitelylongkeystream.ThesecurityofRC4comesfromthesecrecyofthepacketkeythatsderivedfromthekeystream.

vDescribewhataVPNisandhowitworks.

AVPNconnectionistheextensionofaprivatenetworkthatincludeslinksacrosssharedorpublicnetworks,suchastheInternet.VPNconnections(VPNs)enableorganizationstosenddatabetweentwocomputersacrosstheInternetinamannerthatemulatesthepropertiesofapointtopointprivatelink.

Basically,aVPNisaprivatenetworkthatusesapublicnetwork(usuallytheInternet)toconnectremotesitesoruserstogether.Insteadofusingadedicated,realworldconnectionsuchasleasedline,aVPNusesvirtualconnectionsroutedthroughtheInternetfromthecompanysprivatenetworktotheremotesiteoremployee.



VoIP

DescribehowVoIPworks.

VoiceoverInternetProtocol(VoIP),isatechnologythatallowsyoutomakevoicecallsusingabroadbandInternetconnectioninsteadofaregular(oranalog)phoneline.SomeVoIPservicesmayonlyallowyoutocallotherpeopleusingthesameservice,butothersmayallowyoutocallanyonewhohasatelephonenumberincludinglocal,longdistance,mobile,andinternationalnumbers.Also,whilesomeVoIPservicesonlyworkoveryourcomputeroraspecialVoIPphone,otherservicesallowyoutouseatraditionalphoneconnectedtoaVoIPadapter.

DescribemethodsofQoS.

Qualityofserviceistheabilitytoprovidedifferentprioritytodifferentapplications,users,ordataflows,ortoguaranteeacertainlevelofperformancetoadataflow.

QOSisQualityofService:Asetofmetricsusedtomeasurethequalityoftransmissionandserviceavailableofanygiventransmissionsystem

AreyoufamiliarwithIPv6?Ifso,whatarethemajordifferencesbetweenIPv4andIPv6?

IPv6isbasedonIPv4,itisanevolutionofIPv4.SomanythingsthatwefindwithIPv6arefamiliartous.Themaindifferencesare:

1.Simplifiedheaderformat.IPv6hasafixedlengthheader,whichdoesnotincludemostoftheoptionsanIPv4headercaninclude.EventhoughtheIPv6headercontainstwo128bitaddresses(sourceanddestinationIPaddress)thewholeheaderhasafixedlengthof40bytesonly.Thisallowsforfasterprocessing.Optionsaredealtwithinextensionheaders,whichareonlyinsertedaftertheIPv6headerifneeded.Soforinstanceifapacketneedstobefragmented,thefragmentationheaderisinsertedaftertheIPv6header.ThebasicsetofextensionheadersisdefinedinRFC2460.2.Addressextendedto128bits.Thisallowsforhierarchicalstructureoftheaddressspaceandprovidesenoughaddressesforalmosteverygrainofsandontheearth.Importantforsecurityandnewservices/devicesthatwillneedmultipleIPaddressesand/orpermanentconnectivity.3.AlotofthenewIPv6functionalityisbuiltintoICMPv6suchasNeighborDiscovery,Autoconfiguration,MulticastListenerDiscovery,PathMTUDiscovery.4.EnhancedSecurityandQoSFeatures.

IPv4meansInternetProtocolversion4,whereasIPv6meansInternetProtocolversion6.

IPv4is32bitsIPaddressthatweusecommonly,itcanbe192.168.8.1,10.3.4.5orother32bitsIPaddresses.IPv4cansupportupto232addresses,howeverthe32bitsIPv4addressesarefinishingtobeusedinnearfuture,soIPv6isdevelopedasareplacement.

IPv6is128bits,cansupportupto2128addressestofulfillfutureneedswithbettersecurityandnetworkrelatedfeatures.HerearesomeexamplesofIPv6address:

1050:0:0:0:5:600:300c:326b



1050:0:0:0:5:600:300c:326bff06::c30:0:0:0:0:0:192.1.56.10

Whatauthentication,authorizationadaccounting(AAA)mechanismsareyoufamiliarwith?Whichoneshaveyouimplemented??

RADIUSServer(RemoteAccessDialinUserService)

MSIAS(InternetAuthenticaionService)

Comments(11)

11Comments

1. Goodpost!

CommentbytechierantsFebruary6,2012@5:41PM

Reply2. Ilikethispost.

Canyoualsosaysomethingon3Gwirelessnetworkingandprotocolsinvolved?

CommentbyBiggyFebruary9,2012@4:49PM

Replysorrydear,ihavenoexperiencein3gandwififield.

CommentbySyedJahanzaib/Pinochio~:)February9,2012@7:42PM

Reply3. Verymuchinterestingpost.HopetoseethetextonInternationalterrestrialcabling

CommentbyMANaserApril4,2012@2:29PM

Reply4. VeryUsefulStuff,Thanks

CommentbymaheshMay28,2012@1:20PM

Reply5. []MSIAS(InternetAuthenticaionService)Comments(5)[]

PingbackbyGeneralNetworkEngineerInterviewQuestionsGeneralKnowledgeQuestionsYogesh(Yogi)June6,2012@1:31AM

Reply6. goodpost.thanx.



CommentbyranjitAugust20,2012@8:37PM

Reply7. nicepostthanxalot!!!

CommentbymathanDecember15,2012@11:41AM

Reply8. usefulinfowelldone

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Reply9. goodstuffforlesstimeinmoreknowledge.

CommentbyadityaMay8,2013@2:18PM

Reply10. Quitehelpfultounderstandthebasicofnetwork.

CommentbyJonathanJuly30,2013@10:00AM

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