Concept
Switchingisthemethodofmanuallyorautomaticallycompletingthetransmissionoftheinformationtobetransmittedinaccordancewiththeneedsofthetransmissionofinformationatbothendsofthecommunication.Ageneraltermfortechnologiesoncorrespondingroutesthatmeettherequirements.Accordingtodifferentworkingpositions,itcanbedividedintowideareanetworkswitchandlocalareanetworkswitch.Inabroadsense,switchisadevicethatcompletesthefunctionofinformationexchangeinacommunicationsystem.
Inthecomputernetworksystem,theconceptofexchangehasimprovedthesharedworkingmode.TheHUBhubthatweintroducedbeforeisakindofshareddevice.TheHUBitselfcannotidentifythedestinationaddress.WhenthehostAinthesameLANtransmitsdatatothehostB,thedatapacketistransmittedbybroadcastontheHUB-basednetwork.,Eachterminaldetermineswhethertoreceiveitbyverifyingtheaddressinformationinthepacketheader.Thatistosay,inthisworkingmode,onlyonegroupofdataframescanbetransmittedonthenetworkatthesametime,andifacollisionoccurs,ithastoberetried.Thiswayistosharenetworkbandwidth.
Principle
Worksatthedatalinklayer.Theswitchhasahigh-bandwidthbackbusandinternalswitchingmatrix.Alltheportsoftheswitchareconnectedtothisbackbus.Afterthecontrolcircuitreceivesthedatapacket,theprocessingportwilllookuptheaddresscomparisontableinthememorytodeterminethedestinationMAC(thehardwareaddressofthenetworkcard)andtheNIC(networkcard)connectionOnwhichport,thedatapacketisquicklytransmittedtothedestinationportthroughtheinternalswitchingmatrix.IfthedestinationMACdoesnotexist,itwillbebroadcasttoallports.Afterreceivingtheportresponse,theswitchwill"learn"thenewaddressandaddittotheinternalMACAddresstable.Theswitchcanalsobeusedto"segment"thenetwork.BycomparingtheMACaddresstable,theswitchallowsonlynecessarynetworktraffictopassthroughtheswitch.Throughthefilteringandforwardingoftheswitch,thecollisiondomaincanbeeffectivelyreduced,butitcannotdividethenetworklayerbroadcast,thatis,thebroadcastdomain.Theswitchcantransmitdatabetweenmultipleportpairsatthesametime.Eachportcanberegardedasanindependentnetworksegment,andthenetworkequipmentconnectedtoitenjoysthefullbandwidthindependently,anddoesnotneedtocompetewithotherequipmentforuse.WhennodeAsendsdatatonodeD,nodeBcansenddatatonodeCatthesametime,andbothtransmissionsenjoythefullbandwidthofthenetworkandbothhavetheirownvirtualconnections.Ifa10MbpsEthernetswitchisusedhere,thenthetotalcirculationoftheswitchatthistimeisequalto2×10Mbps=20Mbps,andwhena10MbpssharedHUBisused,thetotalcirculationofaHUBwillnotexceed10Mbps.Inshort,aswitchisanetworkdevicebasedonMACaddressrecognitionandcapableofencapsulatingandforwardingdatapackets.Theswitchcan"learn"theMACaddressandstoreitintheinternaladdresstable.Byestablishingatemporaryswitchingpathbetweentheoriginatorandthetargetreceiverofthedataframe,thedataframecandirectlyreachthedestinationaddressfromthesourceaddress.
Technologydevelopmenthistory
Origin
"Switch"isanimportedword,derivedfromtheEnglish"Switch,theoriginalmeaningis"switch",China'stechnicalcirclesareintroducingWhenthiswordistranslatedas"exchange".InEnglish,theverb"exchange"andthenoun"exchange"arethesameword(notethat"exchange"hererefersspecificallytotheexchangeofsignalsintelecommunicationstechnology,andisnotthesameconceptastheexchangeofgoods).
In1993,LANswitchingequipmentappeared.In1994,thedomesticexchangenetworktechnologywasupsurge.Infact,theswitchingtechnologyisaswitchwiththecharacteristicsofsimplicity,lowprice,highperformanceandhighportdensity.Theproduct,thecomplexswitchingtechnologythatembodiesthebridgingtechnology,operatesatthesecondlayeroftheOSIreferencemodel.Likethebridge,theswitchmakesarelativelysimpledecisiontoforwardinformationaccordingtotheMACaddressineachpacket.ThisforwardingdecisiongenerallydoesnotconsiderthepacketThedeeperotherinformationhiddeninthebridge.Thedifferencebetweentheswitchandthebridgeisthattheforwardingdelayoftheswitchissmall,andtheoperationisclosetotheperformanceofasingleLAN,whichfarexceedstheforwardingperformancebetweenordinarybridgedinterconnectionnetworks.
TheswitchingtechnologyallowsThebandwidthofsharedanddedicatedLANsegmentsisadjustedtoreducethebottleneckproblemofinformationcirculationbetweenLANs.Nowadays,thereareswitchingproductsofEthernet,FastEthernet,FDDIandATMtechnology.
SimilarTraditionalbridgesandswitchesprovidemanynetworkinterconnectionfunctions.Theswitchcaneconomicallydividethenetworkintosmallconflictingdomainsandprovidehigherbandwidthforeachworkstation.ThetransparencyoftheprotocolmakestheswitchdirectlyinthecaseofsimplesoftwareconfigurationInstalledinamulti-protocolnetwork;theswitchusesexistingcables,repeaters,hubs,andworkstationnetworkcards,withouttheneedforhigh-levelhardwareupgrades;theswitchistransparenttotheworkstation,sothemanagementoverheadislow,whichsimplifiestheincreaseofnetworknodes,Theoperationofmobileandnetworkchanges.
Usingaspeciallydesignedintegratedcircuit,theswitchcanforwardinformationinparallelonallportsatthelinerate,providingmuchhigheroperatingperformancethantraditionalbridges.AsintheoryAsingleEthernetportpaircontains64octaldatapackets,whichcanprovideatransmissionrateof14880bps.Thismeansthata"linerate"Ethernetswitchwith12portsand6paralleldatastreamsmustprovide89280bpsOverallthroughputrate(6informationstreamsX14880bps/channelinformationstream).ASICtechnologyenablestheswitchtoachievetheaboveperformancewithmoreports,anditsportcostislowerthantraditionalbridges.
Manualexchange
Thehistoryofelectricalsignalexchangeshouldbetracedbacktotheearlydaysoftheappearanceofthetelephone.Whenthetelephonewasinvented,onlyawirelongenough,plustwotelephonesattheend,couldbeseparatedTwopeoplefarawayhaveavoiceconversation.
Asthenumberoftelephonecallsincreases,itisimpossibleforustohavealinebetweeneverytwotelephonesinordertoenableeveryonewhohasatelephonetocommunicatewitheachother.SopeoplesetupInthetelephoneoffice,eachtelephoneuserconnectsalinetoalargecircuitboardinthetelephoneoffice.WhenAwantstotalktoB,heaskstheoperatorofthetelephoneexchangetoconnecttoB'sphone.Theoperatorusesawire,oneendisinsertedintotheholeofAtoconnecttothecircuitboard,andtheotherendisinsertedintotheholeofB.Thisis"connection",whichisequivalenttotemporarilypullingatelephonelineforAandB.Atthistime,bothpartiescanCalled.Whenthecallisover,theoperatorremovesthewire,whichiscalled"disconnection".Thewholeprocessis"manualexchange",whichisactuallyaprocessof"closingtheswitch"and"disconnectingtheswitch".Therefore,translating"exchange"into"switch"istechnicallyeasiertounderstand.
Electronicroutecontrolswitch
Theefficiencyofmanualswitchingistoolowtomeettheneedsoflarge-scaletelephonedeployment.Withthedevelopmentofsemiconductortechnologyandthematurityofswitchingcircuittechnology,peoplehavefoundthatelectronictechnologycanbeusedtoreplacemanualswitching.Aslongasthetelephoneterminalusersendsaseriesofelectricalsignalstotheelectronicdevice,theelectronicdevicecanconnectthecircuitoftherequestingpartyandtherequestedpartyaccordingtoapresetprocedure,andmonopolizethecircuit,andwillnotshareitwithathirdparty(ofcourse,Duetodesignflaws,theremaybesituationswheremultiplepeoplesharethecircuit,whichiscommonlyknownas"serialline").Thistypeofexchangeiscalled"program-controlledexchange".Andthiskindofequipmentisalsocalled"program-controlledswitchboard."
Asthetechnologyofprogram-controlledswitchinghasbeenmonopolizedbydevelopedcountriesforalongtimeandtheequipmentisexpensive,thetelephonepenetrationrateinmycountryhasnotbeenhigh.Withtheindependentdevelopmentofprogram-controlledswitchesbycompaniessuchasHuaweiandZTE,telephoneshaverapidlybecomepopularinmycountry.
Nowadays,thecommunicationprotocolcommonlyusedinvoiceprogram-controlledswitchesisSignallingSystemNo.7
Ethernetswitches
WithcomputersandWiththerapiddevelopmentofitsinterconnectiontechnology(alsoknownas"networktechnology"),Ethernethasbecometheshort-distanceLayer2computernetworkwiththehighestpenetrationratesofar.ThecorecomponentofEthernetistheEthernetswitch.
Whetheritismanualswitchingorprogram-controlledswitching,itisforthetransmissionofvoicesignals,anditisa"circuitswitching"thatrequiresanexclusiveline.TheEthernetisacomputernetworkthatneedstotransmitdata,soituses"packetswitching."Butnomatterwhichswitchingmethodisadopted,theswitch'sfeatureofproviding"exclusiveaccess"betweentwopointswillnotchange.AsfarasEthernetequipmentisconcerned,theessentialdifferencebetweenaswitchandahubisthatwhenAsendsamessagetoB,ifitpassesthroughthehub,allnetworknodesconnectedtothehubwillreceivethisinformation(thatis,itwillbesentintheformofbroadcast),Butthenetworkcardatthehardwarelevelwillfilterouttheinformationthatisnotsenttothemachine;andifitpassesthroughtheswitch,unlessAinformstheswitchtobroadcast,otherwisetheinformationsenttoBwillneverbereceived(obtainingthecontrolauthorityoftheswitchtomonitorthesituationexcept).
Nowadays,Ethernetswitchmanufacturershaveintroducedthree-layerorevenfour-layerswitchesaccordingtomarketdemand.Butinanycase,itscorefunctionisstillLayer2Ethernetdatapacketswitching,butwithacertainabilitytoprocessdatapacketsattheIPlayerorevenhigherlayers.
Opticalswitching
Opticalswitchingisthenextgenerationswitchingtechnologybeingdeveloped.Allswitchingtechnologiestodayarebasedonelectricalsignals.Eventoday’sfiberopticswitchesfirstconvertopticalsignalsintoelectricalsignals,andafterexchangeprocessing,theopticalsignalsarethenconvertedbacktoanotheropticalfiber.Duetothelowphotoelectricconversionrateandthephysicalbottleneckofthecircuitprocessingspeed,peoplehopetodesignan"opticalswitch"thatdoesnotrequirephotoelectricconversion.Theinternalpartisnotacircuitbutanopticalcircuit,andthelogicelementisnotaswitchingcircuit.Itistheswitchopticalpath.Thiswillgreatlyincreasetheprocessingspeedoftheswitch.
Classification
Transmissionmodeoftheswitchhasfullduplex,halfduplex,fullduplex/halfduplexadaptive
Thefullduplexoftheswitchmeansthattheswitchcanalsoreceivedatawhilesendingdata,andthetwoaresynchronized.Thisislikeweusuallymakeaphonecall,andwecanheartheotherparty'svoicewhiletalking.Today'sswitchessupportfullduplex.Theadvantageoffullduplexisthatthedelayissmallandthespeedisfast.
Whenitcomestofull-duplex,onecannotfailtomentionanotherconceptthatcloselycorrespondstoit,whichis"half-duplex."Theso-calledhalf-duplexmeansthatonlyoneactionoccursinaperiodoftime.Asimpleexampleisanarrowroad,andonlyonecarcanpassatthesametime.Whentherearetwocarsdrivinginoppositedirections,inthiscase,onlyonecanpassfirst,andthentheothercandriveaftertheend.Theexamplevividlyillustratestheprincipleofhalf-duplex.Earlywalkie-talkiesandearlyhubswereallproductsthatimplementedhalf-duplex.Withthecontinuousadvancementoftechnology,thehalf-doubleuniongraduallywithdrewfromthestageofhistory.
Inabroadsense,therearetwotypesofnetworkswitches:WANswitchesandLANswitches.WANswitchesaremainlyusedinthetelecommunicationsfieldtoprovideabasicplatformforcommunications.TheLANswitchisusedinthelocalareanetworktoconnecttoterminalequipment,suchasPCsandnetworkprinters.Fromthetransmissionmediumandtransmissionspeed,itcanbedividedintoEthernetswitches,fastEthernetswitches,GigabitEthernetswitches,FDDIswitches,ATMswitches,andtokenringswitches.Fromthescaleofapplication,itcanbedividedintoenterprise-levelswitches,department-levelswitches,andworkgroupswitches.Thescalesofdifferentmanufacturersarenotcompletelythesame.Generallyspeaking,enterprise-levelswitchesarerack-mounted,anddepartment-levelswitchescanberack-mounted(withasmallnumberofslots)orfixed-configurationtype.Thelevelswitchisafixedconfigurationtype(thefunctionisrelativelysimple).Ontheotherhand,fromtheperspectiveofapplicationscale,whenusedasabackboneswitch,aswitchthatsupportslarge-scaleenterpriseapplicationswithmorethan500informationpointsisanenterprise-levelswitch,andaswitchthatsupportsmedium-sizedenterpriseswithlessthan300informationpointsisadepartment-levelswitch,and100Switcheswithinthisinformationpointareworkgroup-levelswitches.TheswitchesintroducedinthisarticlerefertoLANswitches.
Function
Themainfunctionsoftheswitchincludephysicaladdressing,networktopology,errorchecking,framesequenceandflowcontrol.Nowswitchesalsohavesomenewfunctions,suchassupportforVLAN(virtuallocalareanetwork),supportforlinkaggregation,andsomeevenhavethefunctionofafirewall.
Learning:TheEthernetswitchunderstandstheMACaddressofthedeviceconnectedtoeachport,andmapstheaddresstothecorrespondingportandstoresitintheMACaddresstableintheswitchcache.
Forwarding/Filtering:WhenthedestinationaddressofadataframeismappedintheMACaddresstable,itisforwardedtotheportconnectedtothedestinationnodeinsteadofallports(suchasDataframesarebroadcast/multicastframesandthenforwardedtoallports).
Eliminateloops:Whentheswitchincludesaredundantloop,theEthernetswitchusesthespanningtreeprotocoltoavoidloopsandallowsforbackuppaths.
Inadditiontobeingabletoconnecttothesametypeofnetwork,theswitchcanalsointerconnectdifferenttypesofnetworks(suchasEthernetandFastEthernet).Nowadays,manyswitchescanprovidehigh-speedconnectionportsthatsupportFastEthernetorFDDI,etc.,whichareusedtoconnecttootherswitchesinthenetworkorprovideadditionalbandwidthforkeyserversthattakeupalotofbandwidth.
Generallyspeaking,eachportoftheswitchisusedtoconnecttoanindependentnetworksegment,butsometimesinordertoprovidefasteraccessspeed,wecanconnectsomeimportantnetworkcomputersdirectlytotheswitchOntheport.Inthisway,keyserversandimportantusersofthenetworkhavefasteraccessspeedsandsupportgreaterinformationflow.
Finally,brieflysummarizethebasicfunctionsoftheswitch:
1.Likeahub,theswitchprovidesalargenumberofportsforcableconnection,sothatthestartopologycanbeusedforwiring.
2.Likerepeaters,hubs,andbridges,whenitforwardsframes,theswitchregeneratesanundistortedsquareelectricalsignal.
3.Likeabridge,theswitchusesthesameforwardingorfilteringlogiconeachport.
4.Likeabridge,theswitchdividestheLANintomultiplecollisiondomains,andeachcollisiondomainhasanindependentbroadband,thusgreatlyimprovingthebandwidthoftheLAN.
5.Inadditiontothefunctionsofabridge,hub,andrepeater,theswitchalsoprovidesmoreadvancedfeaturessuchasvirtuallocalareanetwork(VLAN)andhigherperformance.
Thedifferencebetweenaswitchandarouter
TraditionalswitchesevolvedfrombridgesandbelongtothesecondlayerofOSI,thedatalinklayerequipment.ItaddressesaccordingtotheMACaddress,selectstheroutethroughthestationtable,andtheestablishmentandmaintenanceofthestationtableareautomaticallycarriedoutbytheswitch.TherouterbelongstothethirdlayerofOSI,thatis,thenetworklayerdevice.ItaddressesaccordingtotheIPaddressandisgeneratedthroughtheroutingtableroutingprotocol.Thebiggestadvantageoftheswitchisthatitisfast.BecausetheswitchonlyneedstoidentifytheMACaddressintheframe,itissimpletogenerateandselecttheforwardingportalgorithmdirectlybasedontheMACaddress,whichisconvenientforASICimplementation,sotheforwardingspeedisextremelyhigh.Buttheworkingmechanismoftheswitchalsobringssomeproblems.
1.Loop:Accordingtoswitchaddresslearningandstationtableestablishmentalgorithm,loopsarenotallowedbetweenswitches.Oncethereisaloop,thespanningtreealgorithmmustbestartedtoblocktheportthatgeneratestheloop.Therouter'sroutingprotocoldoesnothavethisproblem.Therecanbemultiplepathsbetweenrouterstobalancetheloadandimprovereliability.
2.Loadconcentration:Therecanonlybeonepathbetweenswitches,sothatinformationisconcentratedononecommunicationlink,anddynamicdistributionisnotpossibletobalancetheload.Therouter'sroutingprotocolalgorithmcanavoidthis.TheOSPFroutingprotocolalgorithmcannotonlygeneratemultipleroutes,butalsoselectdifferentoptimalroutesfordifferentnetworkapplications.
3.Broadcastcontrol:Theswitchcanonlyreducetheconflictdomain,butnotthebroadcastdomain.Theentireswitchednetworkisalargebroadcastdomain,andbroadcastmessagesarescatteredthroughouttheswitchednetwork.Theroutercanisolatethebroadcastdomain,andbroadcastpacketscannotcontinuetobebroadcastthroughtherouter.
4.Subnetting:TheswitchcanonlyrecognizetheMACaddress.TheMACaddressisaphysicaladdressandusesaflataddressstructure,sothesubnetcannotbedividedaccordingtotheMACaddress.TherouterrecognizestheIPaddress.TheIPaddressisassignedbythenetworkadministrator.ItisalogicaladdressandtheIPaddresshasahierarchicalstructure.Itisdividedintoanetworknumberandahostnumber.Itcanbeeasilyusedtodividesubnets.ThemainfunctionoftherouteristoConnecttodifferentnetworks.
5.Confidentialityissue:AlthoughtheswitchcanalsofiltertheframebasedonthesourceMACaddress,destinationMACaddressandothercontentoftheframe,therouterimplementsthemessagebasedonthesourceIPaddress,destinationIPaddress,TCPportaddressandothercontentofthemessage.Filteringismoreintuitiveandconvenient.
Exchangemethod
Theswitchexchangesinthefollowingthreeways:
1)Straight-through:
Thestraight-throughEthernetswitchcanbeunderstoodasalinematrixtelephoneswitchthatcrossesverticallyandhorizontallybetweeneachport.Whenitdetectsadatapacketattheinputport,itcheckstheheaderofthepacket,obtainsthedestinationaddressofthepacket,activatestheinternaldynamiclookuptabletoconvertitintothecorrespondingoutputport,connectsattheintersectionofinputandoutput,andpassesthedatapacketdirectlytoThecorrespondingportrealizestheswitchingfunction.Sincenostorageisrequired,thedelayisverysmallandtheexchangeisveryfast,whichisitsadvantage.ItsdisadvantageisthatbecausethecontentofthedatapacketisnotsavedbytheEthernetswitch,itcannotcheckwhetherthetransmitteddatapacketiswrong,anditcannotprovideerrordetectioncapabilities.Becausethereisnobuffer,input/outputportswithdifferentspeedscannotbedirectlyconnected,andpacketsareeasilylost.
2)Storeandforward:
StoreandforwardmethodisthemostwidelyusedinthefieldofcomputernetworkTheway.Itstoresthedatapacketoftheinputportfirst,andthenperformsCRC(cyclicredundancycheck)check.Afterprocessingtheerrorpacket,ittakesoutthedestinationaddressofthedatapacket,andconvertsitintotheoutputportthroughalookuptabletosendoutthepacket.Becauseofthis,thestore-and-forwardmethodhasalargedelayindataprocessing,whichisitsshortcoming,butitcanperformerrordetectiononthedatapacketsenteringtheswitchandeffectivelyimprovethenetworkperformance.Itisespeciallyimportantthatitcansupporttheconversionbetweenportsofdifferentspeedsandmaintainthecooperationbetweenhigh-speedportsandlow-speedports.
3)Fragmentationisolation:
Thisisasolutionbetweentheformertwo.Itcheckswhetherthelengthofthedatapacketis64bytes,ifitislessthan64bytes,itmeansitisafakepacket,andthendiscardsthepacket;ifitisgreaterthan64bytes,thepacketissent.Thismethodalsodoesnotprovidedataverification.Itsdataprocessingspeedisfasterthanstore-and-forward,butslowerthanstraight-through.
Severalswitchingtechnologies
Portswitching
Portswitchingtechnologyfirstappearedinslot-typehubs.ThebackplanesofsuchhubsareusuallydividedintomanyEthernetsegments(eachnetworksegmentisabroadcastdomain),donotneedtobeconnectedbyabridgeorroute,andthenetworksarenotconnectedtoeachother.Afteralargemainmoduleisinserted,itisusuallyallocatedtoanetworksegmentofabackplane.PortswitchingisusedtodistributeandbalancetheportsoftheEthernetmoduleamongmultiplenetworksegmentsofthebackplane.Accordingtothedegreeofsupport,portswitchingcanalsobesubdividedinto:
·Moduleswitching:Theentiremoduleismigratedtothenetworksegment.
·Portgroupexchange:Usuallytheportsonthemodulearedividedintoseveralgroups,andeachgroupofportsallowsnetworksegmentmigration.
·Port-levelswitching:supporteachporttomigratebetweendifferentnetworksegments.ThisswitchingtechnologyisbasedonthefirstlayerofOSIandhastheadvantagesofflexibilityandloadbalancingcapabilities.Ifconfiguredproperly,itcanbefault-toleranttoacertainextent,butitdoesnotchangethecharacteristicsofthesharedtransmissionmedium,andthuscannotbecalledatrueexchange.
Frameswitching
FrameswitchingiscurrentlythemostwidelyusedLANswitchingtechnology.Itprovidesaparalleltransmissionmechanismthroughmicro-segmentationoftraditionaltransmissionmediatoreduceconflictareas.Obtainhighbandwidth.Generallyspeaking,theimplementationtechnologyofeachcompany'sproductswillbedifferent,buttheprocessingmethodsfornetworkframesaregenerallyasfollows:Thefirst14bytesoftheframewilltransmitthenetworkframetothecorrespondingport.
Storeandforward:Checkandcontrolerrorsbyreadingnetworkframes.
Theexchangespeedoftheformermethodisveryfast,butitlacksmoreadvancedcontrolofnetworkframes,lacksintelligenceandsecurity,andcannotsupporttheexchangeofportswithdifferentrates.Therefore,variousmanufacturersfocusonthelattertechnology.
Somemanufacturersevendecomposethenetworkframeintofixed-sizecells.Thecellprocessingisextremelyeasytoimplementwithhardware,andtheprocessingspeedisfast.Atthesametime,itcancompleteadvancedcontrolfunctions(suchastheUnitedStates).MADGE'sLEThub)suchasprioritycontrol.
Cellexchange
ATMtechnologyusesafixed-length53-bytecellexchange.Sincethelengthisfixed,itiseasytoimplementinhardware.ATMusesdedicatednon-differentiatedconnectionsandrunsinparallel.Multiplenodescanbeestablishedatthesametimethroughaswitch,butitwillnotaffectthecommunicationcapabilitiesbetweeneachnode.ATMalsoallowsmultiplevirtuallinkstobeestablishedbetweenthesourcenodeandthetargetandnodetoensuresufficientbandwidthandfaulttolerance.ATMusesstatisticaltime-divisioncircuitsformultiplexing,whichcangreatlyimprovechannelutilization.ThebandwidthofATMcanreach25M,155M,622MandevenseveralGbtransmissioncapacity.Butwiththeemergenceof10GigabitEthernet,ATMtechnology,whichoncerepresentedthefuturedirectionofnetworkandcommunicationtechnologydevelopment,begantograduallyloseitsmeaning.
Developmentprospects
Asthemainconnectiondeviceforlocalareanetworks,Ethernetswitcheshavebecomeoneofthemostpopularnetworkdevices.Withthecontinuousdevelopmentofswitchingtechnology,thepriceofEthernetswitcheshasdroppedsharply,andswitchingtothedesktophasbecomeageneraltrend.
Ifyouhavealargenumberofusers,busyapplications,andvariousserversonyourEthernetnetwork,andyouhavenotmadeanyadjustmentstothenetworkstructure,thentheperformanceoftheentirenetworkmaybeveryLow.Oneofthesolutionsistoadda10/100MbpsswitchtotheEthernet,whichcannotonlyhandle10MbpsregularEthernetdataflow,butalsosupports100MbpsfastEthernetconnection.
Iftheutilizationrateofthenetworkexceeds40%,andthecollisionrateisgreaterthan10%,theswitchcanhelpyousolvealittleproblem.Switcheswith100MbpsFastEthernetand10MbpsEthernetportscanoperateinfullduplexmodeandcanestablishadedicated20Mbpsto200Mbpsconnection.
Notonlytheroleofswitchesindifferentnetworkenvironmentsisdifferent,theimpactofaddingnewswitchesandaddingswitchportsofexistingswitchestothenetworkinthesamenetworkenvironmentisalsodifferent.Fullyunderstandingandmasteringtheflowpatternofthenetworkisaveryimportantfactorinwhethertheswitchcanfunction.Becausethepurposeofusingaswitchistoreduceandfilterthedatatrafficinthenetworkasmuchaspossible,soifaswitchinthenetworkisinstalledincorrectlyandalmostneedstoforwardallthereceiveddatapackets,theswitchwillnotbeabletooptimizethenetwork.Theeffectofperformance,onthecontrary,reducesthedatatransmissionspeedandincreasesthenetworkdelay.
Inadditiontotheinstallationlocation,ifaswitchisalsoblindlyaddedtoanetworkwithasmallloadandalowamountofinformation,itmayalsohaveanegativeimpact.Affectedbyfactorssuchastheprocessingtimeofthedatapacket,thebuffersizeoftheswitchandtheneedtoregeneratenewdatapackets,inthiscase,itismoreidealtouseasimpleHUBthanaswitch.Therefore,wecannotassumethattheswitchhasadvantagesovertheHUB,especiallywhentheuser'snetworkisnotcongestedandthereisstillalotofusablespace,theuseoftheHUBcanmakefulluseoftheexistingresourcesofthenetwork.
Thedifferencebetweenthenumberoflayers
Layer2switch,thedifferencebetweenLayer3switchandLayer4switch
Layer2switch
Thedevelopmentofthetwo-layerswitchingtechnologyisrelativelymature.Thetwo-layerswitchisadatalinklayerdevice.ItcanidentifytheMACaddressinformationinthedatapacket,forwarditaccordingtotheMACaddress,andrecordtheseMACaddressesandthecorrespondingportsintheInanaddresstablewithinoneself.
Thespecificworkflowisasfollows:
1)Whentheswitchreceivesadatapacketfromacertainport,itfirstreadsthesourceMACaddressinthepacketheader,sothatitknowsthesourceWhichportthemachinewiththeMACaddressisconnectedto;
2)ThenreadthedestinationMACaddressintheheader,andlookupthecorrespondingportintheaddresstable;
3)IfthereisaportcorrespondingtothedestinationMACaddressinthetable,copythedatapacketdirectlytothisport;
4)Ifthecorrespondingportisnotfoundinthetable,broadcastthedatapackettoallportsAbove,whenthedestinationmachinerespondstothesourcemachine,theswitchcanrecordwhichportthedestinationMACaddresscorrespondsto,anditisnolongernecessarytobroadcasttoallportswhentransmittingdatanexttime.Thisprocessisrepeatedcontinuously,andtheMACaddressinformationoftheentirenetworkcanbelearned.ThisishowtheLayer2switchestablishesandmaintainsitsownaddresstable.
FromtheworkingprincipleoftheLayer2switch,thefollowingthreepointscanbeinferred:
1)Sincetheswitchexchangesdataofmostportsatthesametime,thisrequiresawideswitchingbusbandwidthIftheLayer2switchhasNports,thebandwidthofeachportisM,andthebusbandwidthoftheswitchexceedsN×M,thentheswitchcanrealizewire-speedswitching.
2)Learntheport-connectedmachineMACaddress,writtenintotheaddresstable,thesizeoftheaddresstable(generallytworepresentations:oneisBEFFERRAM,theotheristhevalueoftheMACtableentry),thesizeoftheaddresstableaffectstheaccesscapacityoftheswitch
3)AnotheristhatLayer2switchesgenerallycontainASIC(ApplicationSpecificIntegratedCircuit)chipsthatarespeciallyusedtoprocessdatapacketforwarding,sotheforwardingspeedcanbeveryfast.AseachmanufacturerusesdifferentASICs,itdirectlyaffectsproductperformance.
TheabovethreepointsarealsothemaintechnicalparametersforjudgingtheperformanceofLayer2andLayer3switches.Pleasepayattentiontocomparisonwhenconsideringequipmentselection.
Three-layerswitch
Let’stakealookattheworkingprocessofthethree-layerswitchthroughasimplenetwork.
DeviceAusingIP------------------------Layer3switch------------------------DeviceBusingIP
Forexample,ifAwantstosenddatatoB,knowingthedestinationIP,thenAusesthesubnetmasktoobtainthenetworkaddress,DeterminewhetherthedestinationIPisinthesamenetworksegmentasyourself.Ifyouareonthesamenetworksegment,butdon’tknowtheMACaddressrequiredtoforwardthedata,AsendsanARPrequest,BreturnsitsMACaddress,AusesthisMACtoencapsulatethedatapacketandsendsittotheswitch,andtheswitchusestheLayer2switchingmoduletofindMACaddresstable,forwardthedatapackettothecorrespondingport.
IfthedestinationIPaddressisnotinthesamenetworksegment,thenAneedstocommunicatewithB.IfthereisnocorrespondingMACaddressentryintheflowcacheentry,thefirstnormaldatapacketwillbesenttoafault.Provincialgateway.Thisdefaultgatewayisgenerallysetintheoperatingsystem.TheIPofthisdefaultgatewaycorrespondstothethirdlayerroutingmodule,sofordatathatisnotinthesamesubnet,thedefaultgatewayisthefirsttobeplacedintheMACtableTheMACaddress(completedbythesourcehostA);thenthethree-layermodulereceivesthedatapacket,andqueriestheroutingtabletodeterminetheroutetoB.Anewframeheaderwillbeconstructed,inwhichtheMACaddressofthedefaultgatewayisThesourceMACaddress,withtheMACaddressofhostBasthedestinationMACaddress.Throughacertainrecognitiontriggermechanism,establishthecorrespondingrelationshipbetweentheMACaddressesandforwardingportsofhostAandB,andrecorditintotheflowcacheentrytable,andthesubsequentdatafromAtoB(thelayerthreeswitchmustconfirmthatitisfromAtoBinsteadofForthedatatoC,theIPaddressintheframemustberead.),itisdirectlyhandedovertotheLayer2switchingmoduleforcompletion.Thisisusuallyreferredtoasonerouteandmultipleforwarding.
Theaboveisabriefsummaryoftheworkingprocessofthethree-layerswitch,youcanseethecharacteristicsofthethree-layerswitch:1)Thecombinationofhardwarerealizesthehigh-speeddataforwarding.ThisisnotasimplesuperpositionofLayer2switchesandrouters.Layer3routingmodulesaredirectlysuperimposedonthehigh-speedbackplanebusofLayer2switching,breakingthroughtheinterfaceratelimitoftraditionalrouters,andtheratecanreachdozensofGbit/s.Countingthebackplanebandwidth,thesearetwoimportantparametersfortheperformanceoftheLayer3switch.
2)Theconciseroutingsoftwaresimplifiestheroutingprocess.Mostofthedataforwarding,exceptforthenecessaryrouting,ishandledbytheroutingsoftware,anditisforwardedathighspeedbytheLayer2module.Mostoftheroutingsoftwareisprocessedandoptimizedsoftware,notsimplycopyingthesoftwareintherouter.
Layer2andLayer3switchThechoice
Layer2switchisusedforsmallLocalareanetwork.Needlesstosay,inasmalllocalareanetwork,broadcastpacketshavelittleeffect.Thefastswitchingfunction,multipleaccessports,andlowpricesofLayer2switchesprovidesmallnetworkuserswithaverycompletesolution.
Theadvantageofathree-layerswitchisthatithasrichinterfacetypes,supportspowerfulthree-layerfunctions,andpowerfulroutingcapabilities.Itissuitableforroutingbetweenlargenetworks.Itsadvantageliesinselectingthebestrouteandloadsharing.Linkbackupandexchangeofroutinginformationwithothernetworks,etc.routershavefunctions.
Themostimportantfunctionofthethree-layerswitchistospeedupthefastforwardingofdatawithinalargelocalareanetwork.Theadditionoftheroutingfunctionalsoservesthispurpose.Ifalarge-scalenetworkisdividedintosmallLANsaccordingtodepartments,regionsandotherfactors,thiswillleadtoalargenumberofinter-internetvisits,andthesimpleuseofLayer2switchescannotachieveinter-internetvisits;suchasthesimpleuseofrouters,duetothelimitednumberofinterfacesandTheroutingandforwardingspeedisslow,whichwilllimitthenetworkspeedandnetworkscale.Theuseofafastforwardingthree-layerswitchwithroutingfunctionbecomesthefirstchoice.
Generallyspeaking,inanetworkwithlargeinternalnetworkdatatrafficandfastforwardingandresponse,ifallthethree-layerswitchesdothiswork,thethree-layerswitcheswillbeoverloadedandtheresponsespeedwillbeaffected.Itisagoodnetworkingstrategytogivefullplaytotheadvantagesofdifferentdevicestocompletetheroutingbetweenthenetworksbyrouters.Ofcourse,thepremiseisthatthecustomer’spocketsareverybulging,otherwiseitisbettertogiveprioritytothethree-layerswitch.ItalsoservesasInternetinterconnection.
Layer4switching
Asimpledefinitionoflayer4switchingis:itisafunctionthatdeterminestransmissionnotonlybasedonMACaddress(layer2bridge)orsource/DestinationIPaddress(layer3routing),andportnumberaccordingtoTCP/UDP(layer4)application.ThefourthlayerswitchingfunctionislikeavirtualIP,pointingtoaphysicalserver.Ittransmitsservicessubjecttovariousprotocols,includingHTTP,FTP,NFS,Telnetorotherprotocols.Theseservicesrequirecomplexloadbalancingalgorithmsbasedonphysicalservers.
IntheIPworld,theservicetypeisdeterminedbytheterminalTCPorUDPportaddress,andtheapplicationintervalinthefourthlayerexchangeisdeterminedbythesourceandterminalIPaddresses,TCPandUDPports.Inthefourthlayerofexchange,avirtualIPaddress(VIP)issetupforeachservergroupforsearching,andeachgroupofserverssupportsacertainapplication.Eachapplicationserveraddressstoredinthedomainnameserver(DNS)isaVIP,notarealserveraddress.Whenauserappliesforanapplication,aVIPconnectionrequest(suchasaTCPSYNpacket)withatargetservergroupissenttotheserverswitch.Theserverswitchselectsthebestserverinthegroup,replacestheVIPintheterminaladdresswiththeIPoftheactualserver,andtransmitstheconnectionrequesttotheserver.Inthisway,allpacketsinthesamesectionaremappedbytheserverswitchandtransmittedbetweentheuserandthesameserver.
ThefourthlayerofexchangePrinciple
ThefourthlayeroftheOSImodelisthetransportlayer.Thetransportlayerisresponsibleforend-to-endcommunication,thatis,coordinatedcommunicationbetweennetworksourceandtargetsystems.IntheIPprotocolstack,thisistheprotocollayerwhereTCP(atransmissionprotocol)andUDP(userdatapacketprotocol)arelocated.
Inthefourthlayer,TCPandUDPheaderscontainportnumbers,whichcanuniquelydistinguishwhichapplicationprotocols(suchasHTTP,FTP,etc.)eachdatapacketcontains.Theendpointsystemusesthisinformationtodistinguishthedatainthepacket,especiallytheportnumbersothatareceivingcomputersystemcandeterminethetypeofIPpacketitreceives,andhanditovertotheappropriatehigh-levelsoftware.ThecombinationofportnumberanddeviceIPaddressisusuallycalled"socket".Portnumbersbetween1and255arereserved,andtheyarecalled"familiar"ports,thatistosay,theseportnumbersarethesameinallhostTCP/IPprotocolstackimplementations.Inadditionto"familiar"ports,standardUNIXservicesareallocatedintherangeof256to1024ports,andcustomapplicationsgenerallyallocateportnumbersabove1024.ThelistofassignedportnumberscanbefoundonRFC1700"AssignedNumbers".
TheadditionalinformationprovidedbytheTCP/UDPportnumbercanbeusedbythenetworkswitch,whichisthebasisofthefourthlayerofexchange.Theswitchwiththefourthlayerfunctioncanplaytheroleofthe"virtualIP"(VIP)frontendconnectedwiththeserver.EachserverandservergroupsupportingasingleorgeneralapplicationisconfiguredwithaVIPaddress.ThisVIPaddressissentoutandregisteredonthedomainnamesystem.Whensendingaservicerequest,thefourthlayerswitchrecognizesthebeginningofasessionbydeterminingthestartofTCP.Itthenusescomplexalgorithmstodeterminethebestservertohandlethisrequest.Oncethisdecisionismade,theswitchassociatesthesessionwithaspecificIPaddressandreplacestheVIPaddressontheserverwiththerealIPaddressoftheserver.
EachLayer4switchsavesaconnectiontableassociatedwiththesourceIPaddressandsourceTCPportoftheselectedserver.Thenthefourthlayerswitchforwardstheconnectionrequesttothisserver.Allsubsequentpacketsarere-mappedandforwardedbetweentheclientandtheserveruntiltheswitchdiscoverstheconversation.Inthecaseofusingthefourthlayerofswitching,accesscanbeconnectedwithrealserverstomeetuser-definedrules,suchashavinganequalnumberofaccessesoneachserverorallocatingtransmissionstreamsaccordingtothecapacityofdifferentservers.
Howtochooselayer4switching
1)Speed
Inordertobeeffectiveintheenterprisenetwork,layer4switchingmustProvidesperformancecomparabletoLayer3wire-speedrouters.Inotherwords,Layer4switchingmustoperateatfullmediaspeedonallports,evenonmultipleGigabitEthernetconnections.GigabitEthernetspeedisequivalenttoroutingatthemaximumspeedof1488000packetspersecond(assumingtheworst-casescenario,thatis,allpacketsaretheminimumsizedefinedbythenetworkandare64byteslong).
2)Servercapacitybalancealgorithm
Accordingtothedesiredcapacitybalanceintervalsize,therearemanyalgorithmsfortheallocationofapplicationstoserversbythefourthlayerswitch,Thereisasimpledetectionofthenearestconnectionoftheloop,detectionoftheloopdelayorclosed-loopfeedbackoftheserveritself.Ofallthepredictions,closed-loopfeedbackprovidesthemostaccuratedetectionthatreflectstheexistingbusinessvolumeoftheserver.
3)Tablecapacity
Itshouldbenotedthattheswitchthatperformsthefourthlayerexchangeneedstohavetheabilitytodistinguishandstorealargenumberofsenttableitems.Thisisespeciallytruewhentheswitchisatthecoreofanenterprisenetwork.ManyLayer2/3switchestendtosendthesizeofthetableindirectproportiontothenumberofnetworkdevices.ForLayer4switches,thisnumbermustbemultipliedbythenumberofdifferentapplicationprotocolsandsessionsusedinthenetwork.Therefore,thesizeofthesendingtableincreasesrapidlywiththenumberofendpointdevicesandapplicationtypes.Layer4switchdesignersneedtoconsiderthisgrowthintableswhendesigningtheirproducts.Alargetablecapacityisessentialformanufacturinghigh-performanceswitchesthatsupportwire-speedtransmissionofLayer4traffic.
4)Redundancy
Thefourthlayerswitchhasthefunctionofsupportingredundanttopologystructure.Inthecaseofafault-tolerantconnectionwithadual-linknetworkcard,itispossibletoestablishacompletelyredundantsystemfromaservertothenetworkcard,linkandserverswitch.
Managementmethods
Thenetworkmanagementswitchcanbemanagedinthefollowingways:managementthroughtheRS-232serialport(orparallelport),managementthroughawebbrowser,andthroughthenetworkManagementsoftwaremanagement.
Manageviaserialport
Thenetworkmanagementswitchcomeswithaserialcableforswitchmanagement.Firstplugoneendoftheserialcableintotheserialportonthebackoftheswitch,andplugtheotherendintotheserialportofanordinarycomputer.Thenpowerontheswitchandthecomputer.The"HyperTerminal"programisprovidedinbothWindows98andWindows2000.Openthe"HyperTerminal",aftersettingtheconnectionparameters,youcaninteractwiththeswitchthroughtheserialcable.Thismethoddoesnotoccupythebandwidthoftheswitch,soitiscalled"Outofband"(Outofband).
Inthismanagementmode,theswitchprovidesamenu-drivenconsoleinterfaceorcommandlineinterface.Youcanusethe"Tab"keyorarrowkeystomovethroughthemenusandsubmenus,presstheEnterkeytoexecutethecorrespondingcommands,orusethededicatedswitchmanagementcommandsettomanagetheswitch.Switchesofdifferentbrandshavedifferentcommandsets,andevenswitchesofthesamebrandhavedifferentcommands.Usingmenucommandsismoreconvenientinoperation.
ManagementviaWeb
ThenetworkmanagementswitchcanbemanagedviatheWeb(webbrowser),butanIPaddressmustbeassignedtotheswitch.ThisIPaddresshasnootherpurposeexceptforthemanagementswitch.Inthedefaultstate,theswitchdoesnothaveanIPaddress.YoumustspecifyanIPaddressthroughtheserialportorothermethodstoenablethismanagementmethod.
Whenusingawebbrowsertomanagetheswitch,theswitchisequivalenttoawebserver,butthewebpageisnotstoredintheharddisk,butintheNVRAMoftheswitch.ThewebprogramintheNVRAMcanbeupgradedthroughtheprogram.WhentheadministratorenterstheIPaddressoftheswitchinthebrowser,theswitchislikeaservertopassthewebpagetothecomputer,anditfeelslikeyouarevisitingawebsiteatthistime.Thismethodoccupiesthebandwidthoftheswitch,soitiscalled"inbandmanagement"(Inband).
Ifyouwanttomanagetheswitch,justclickthecorrespondingfunctionitemonthewebpageandchangetheswitchparametersinthetextboxordrop-downlist.Webmanagementcanbecarriedoutonthelocalareanetworkinthisway,soremotemanagementcanberealized.
Managedthroughnetworkmanagementsoftware
ThenetworkmanagementswitchesallfollowtheSNMPprotocol(SimpleNetworkManagementProtocol),whichisasetofnetworkequipmentmanagementspecificationsthatcomplywithinternationalstandards.AlldevicesthatfollowtheSNMPprotocolcanbemanagedthroughnetworkmanagementsoftware.YouonlyneedtoinstallasetofSNMPnetworkmanagementsoftwareonanetworkmanagementworkstation,andyoucaneasilymanagetheswitches,routers,servers,etc.onthenetworkthroughtheLAN.Itisalsoanin-bandmanagementmethodthroughtheinterfaceofSNMPnetworkmanagementsoftware.
Themanagementofthenetworkmanagementswitchcanbemanagedintheabovethreeways.Whichmethodisused?Whentheswitchisinitiallysetup,itisoftenthroughout-of-bandmanagement;aftersettingtheIPaddress,youcanusein-bandmanagement.In-bandmanagementBecausethemanagementdataistransmittedthroughapubliclyusedLAN,remotemanagementcanbeachieved,butthesecurityisnotstrong.Out-of-bandmanagementisthroughserialcommunication,anddataisonlytransferredbetweentheswitchandthemanagementmachine,sothesecurityisverystrong;however,duetothelimitationofthelengthoftheserialcable,remotemanagementcannotberealized.Sowhichmethodyouusedependsonyourrequirementsforsecurityandmanageability.
Selectioncriteria
Switchesareveryimportant.Heholdsthelifebloodofanetwork,sohowtochooseaswitch?Whatswitch?Theprosandconsofaswitchareundoubtedlyveryimportantwhenpurchasingaswitch,andtheprosandconsofaswitchshouldstartwiththeoverallarchitecture,performanceandfunctions.
Whenpurchasingaswitch.Intermsofperformance,inadditiontomeetingthebasicstandardsrecommendedbyRFC2544,namelythroughput,delay,andpacketlossrate,asuserservicesincreaseandapplicationsdeepen,itmustalsomeetsomeadditionalindicators,suchasthenumberofMACaddressesandroutingtables.Capacity(Layer3switch),ACLnumber,LSPcapacity,numberofsupportedVPNs,etc.
Switchfunctionisthemostdirectindicator
Generalaccesslayerswitch,simpleQoSguarantee,securitymechanism,supportnetworkmanagementstrategy,spanningtreeprotocolandVLANisanindispensablefunction.Aftercarefulanalysis,somefunctionsarefurthersubdivided.Thesesubdividedfunctionsarethemainreasonforproductdifferencesandanimportantwaytoreflecttheaddedvalueofproducts.
Application-levelQoSguaranteeoftheswitch
TheQoSpolicyoftheswitchsupportsmulti-levelpacketpriorityPrioritysettingsforIPaddressesandportsprovideInternetcafeownerswithgreaterflexibilityinpracticalapplications.Atthesametime,theexchangemachinehasgoodcongestioncontrolandflowrestrictioncapabilities,supportsDiffservdifferentiatedservices,andcanintelligentlydistinguishdifferentapplicationstreamsaccordingtothesource/destinationMAC/IP,soastomeettheneedsofmultimediaapplicationsinreal-timeInternetcafes..NotethatsomeswitchesonthemarketnowclaimtohaveQoSguarantees,butinfacttheyonlysupportsingle-levelprioritysettings,whichbringsalotofinconveniencetopracticalapplications.AllInternetcafeownersneedtopayattentionwhenpurchasing.
TheswitchshouldhaveVLANsupport
VLANisavirtuallocalareanetwork.BydividingthelocalareanetworkintovirtualnetworkVLANnetworksegments,networkmanagementandnetworksecuritycanbestrengthened.Tocontrolunnecessarydatabroadcasts,theworkinggroupinthenetworkcanbreakthroughthegeographicallocationrestrictionsinthesharednetwork,anddividesubnetsaccordingtomanagementfunctions.SwitchesofdifferentmanufacturershavedifferentsupportcapabilitiesforVLANs,andthenumberofVLANssupportedisalsodifferent.
Theswitchshouldhaveanetworkmanagementfunction
SNMP,RMON,etc.management.Usually,switchmanufacturersprovidemanagementsoftwareorthird-partymanagementsoftwaretoremotelymanagetheswitch.GeneralswitchesmeetSNMPMIBI/MIBIIstatisticalmanagementfunctions,andsupportconfigurationmanagement,qualityofservicemanagement,alarmmanagementandotherstrategies,whilemorecomplexGigabitswitcheswillsupportRMONactivemonitoringbyaddingabuilt-inRMONgroup(mini-RMON).
Theswitchshouldsupportlinkaggregation
LinkaggregationcanmakethelinkbandwidthbetweentheswitchesandbetweentheswitchandtheserverhaveverygoodscalabilityForexample,two,three,andfourgigabitlinkscanbeboundtogethertodoublethebandwidthofthelink.Thelinkaggregationtechnologycanachieveloadbalancingofdifferentports,andatthesametimecanbackupeachothertoensuretheredundancyofthelink.InsomeGigabitEthernetswitches,upto4groupsoflinkaggregationcanbesupported,withamaximumof4portsineachgroup.However,therearealsoswitchesthatsupport8groupsoflinkaggregation,suchastheVS-5524GF,whichisasafetylinkageswitchofVolkswagen,whichhas8groupsoflinkaggregation,eachwithamaximumof8ports.Bothspanningtreeprotocolandlinkaggregationcanensuretheredundancyofanetwork.Setupredundantlinksinanetwork,anduseSpanningTreeProtocoltoblockthebackuplink.Logically,itdoesnotformaloop.Onceafailureoccurs,thebackuplinkisenabled.
TheswitchmustsupporttheVRRPprotocol
VRRP(VirtualRoutingRedundancyProtocol)isasolutiontoensurenetworkreliability.Inthisprotocol,thedefaultgateway(DefaultGateway)oftheterminalIPdeviceonthesharedmulti-accessaccessmediumisredundantlybackedup,sothatwhenoneofthethree-layerswitchdevicesgoesdown,thebacked-updevicewilltakeovertheforwardingworkintime,Theuserprovidestransparenthandover,whichimprovesthequalityofnetworkservice.TheVRRPprotocolissimilartoCisco'sHSRPprotocol,butHSRPisproprietarytoCisco.Today,mainstreamswitchmanufacturershavealreadysupportedtheVRRPprotocolintheirproducts,butitwilltaketimeforthemtobewidelyused.
Brandmodelintroduction
Huaweiswitch
LI(LitesoftwareImage)meansthedeviceisaweakfeatureversion.
SI(StandardsoftwareImage)meansthatthedeviceisastandardversionandincludesbasicfeatures.
EI(EnhancedsoftwareImage)meansthatthedeviceisanenhancedversionandcontainssomeadvancedfeatures.
HI(HypersoftwareImage)meansthatthedeviceisanadvancedversionandcontainssomemoreadvancedfeatures
Zmeansthatthereisnouplinkinterface;(newproductsdonotallowthisbit)
G,meanstheupstreamGBICinterface
P,meanstheupstreamSFPinterface
T,meanstheupstreamRJ45interface
V,meanstheupstreamVDSLinterface
W,indicatesthattheupstreamWANinterfacecanbeconfigured
C,indicatesthattheupstreaminterfaceisoptional
M,indicatesthattheupstreaminterfaceisamultimodeopticalport
S,indicatesthattheupstreaminterfaceisasingle-modeopticalinterface
F,indicatesthatthedownstreaminterfaceisatemplateboard,whichcanbepluggedintoanopticalinterfaceboardoranelectricalinterfaceboard.Itismainlycompatiblewiththenamingofoldproductssuchas3526F,3526EF,3552F.
Whenitexistsatthesametime,itmeansthattheuplinkinterfaceisacompositeofmultipleinterfacetypes
Note:Comboportisnotdisplayedinthename.
CiscoSwitch
TeachyoutoidentifythemodelofCiscoswitchinthenetworkworld.CiscoSystemInc.intheUnitedStatescanbesaidtobeknowntoeveryone.WithitsIOS(InternetOperatingSystem),Ciscoisanabsoluteleaderinthemulti-protocolroutermarket.Today,nearly80%ofroutersintheInternetcomefromCisco.Infact,inadditiontothemainproductofrouters,Ciscoalsohasafulllineofnetworkequipment,includinghubs,switches,accessservers,softandhardfirewalls,networkmanagementsoftware,andsoon.Ciscopaysgreatattentiontothetrackingofnewtechnologies.Throughaseriesofcooperationandmergers,Ciscohassuccessfullysteppedintoemergingmarketssuchasbroadbandaccessandwirelesscommunications.
ThisarticlemainlyintroducesCisco'sswitchproductlineandmainproducts.
I.Overview
Cisco’sswitchproductsarebrandedwith"Catalyst",including1900,2800,2900,3500,4000,5000,5500,Morethantenseriessuchas6000and8500.Ingeneral,theseswitchescanbedividedintotwocategories:
Onecategoryisafixedconfigurationswitch,includingmostmodelsof3500andbelow,forexample,1924isa24-port10MEthernetswitchwithtwo100Muplinksport.Exceptforlimitedsoftwareupgrades,theseswitchescannotbeexpanded;
Theothertypeismodularswitches,mainlyreferringtomodelsof4000andabove.Networkdesignerscanchoosedifferentnumbersandmodelsaccordingtonetworkrequirements.Theinterfaceboard,powersupplymoduleandcorrespondingsoftware.
Whenchoosingequipment,manypeoplehaveaheadacheforthelongproductmodel.Infact,Ciscohascertainrulesonthenamingofproducts.ForCatalystswitches,theformatofproductnamingisasfollows:
CatalystNNXX[-C][-M][-A/-EN]
Amongthem,NNistheswitch’sSerialnumber,XXisthenumberofportsforafixedconfigurationswitch,andthenumberofslotsforamodularswitch.The-Csignindicatesthatithasanopticalfiberinterface,-Mindicatesmodularity,and-Aand-ENrefertotheswitchrespectively.Thesoftwareisstandardboardorenterpriseedition.
Second,productintroduction
Nowadays,thecommonCiscoswitchesinnetworkintegrationprojectshavethefollowingseries,1900/2900series,3500series,6500series.Theyareusedinthelow-end,mid-end,andhigh-endofthenetwork.Let’sintroducetheproductsoftheseseriesrespectively:
1.Low-endproducts
Let’stalkaboutthelow-endproductsfirst.1900and2900arelow-endproducts.Typicalofendproducts.Infact,inthelow-endswitchmarket,Ciscodoesnothaveaspecialadvantage,becausetheproductsofcompaniessuchas3ComandDlinkhaveabetterprice-performanceratio.
The1900switchissuitablefordesktopcomputeraccessattheendofthenetworkandisatypicallow-endproduct.Itprovides12or2410Mportsand2100Mports,amongwhich100Mportssupportfull-duplexcommunicationandcanprovideupto200Mbpsportbandwidth.Thebackplanebandwidthofthemachineis320Mbps.
2.Mid-rangeproducts
Let’slookatmid-rangeproducts.Amongthemid-rangeproducts,the3500seriesiswidelyusedandveryrepresentative.
ThebasicfeaturesofC3500seriesswitchesincludebackplanebandwidthupto10Gbps,forwardingrate7.5Mpps,itsupports250VLANs,supportsIEEE802.1QandISLTrunking,supportsCGMPnetwork/GigabitEthernetswitches,Chooseredundantpowersupplyandsoon.ButthebiggestfeatureofC3500ismanagementandgigabit.
Intermsofmanagementfeatures,C3500implementsCisco'sswitchingclustertechnology,whichcaninterconnect16switchesoftheC3500,C2900,andC1900series,andmanagethemthroughanIPaddress.TheCiscoVisualSwitchManager(CVSM)softwareintheC3500canalsobeusedtoconvenientlysetupandmanagetheswitchthroughabrowser.
IntermsofGigabitfeatures,C3500fullysupportsGigabitInterfaceCard(GBIC).NowGBIChasthreekindsof1000BaseSx,suitableformultimodefiber,thelongestdistanceis550m;1000BaseLX/LH,bothmultimode/singlemodefiberaresuitable,thelongestdistanceis10km;1000BaseZXissuitableforsinglemodefiber,thelongestdistanceis100km.
C3500mainlyhas4models:
Catalyst3508GXL:8-portGBICslot
Catalyst3512XL:12-port10/100Madaptive,2PortGBICslot
Catalyst3524XL:24-port10/100Madaptive,2-portGBICslot
Catalyst3548XL:48-port10/100Madaptive,2-portGBICSlots
3.High-endproducts
Finally,introducehigh-endproducts.Forenterprisedatanetworks,theC6000seriesreplacestheoriginalC5000seriesandisthemostcommonlyusedproduct.
Catalyst6000seriesswitchesprovidehigh-performance,multi-layerswitchingsolutionsforcampusnetworks,specificallydesignedforapplicationenvironmentsthatrequiregigabitexpansion,highavailability,andmulti-layerswitching,andaremainlyforcampusbackboneconnections,etc.occasion.
TheCatalyst6000seriesiscomposedoftwomodelsofswitches,Catalyst6000andCatalyst6500,bothofwhichcontain6or9slotmodels,namely6006,6009,6506and6509,amongwhich,6509Themostwidelyused.Allmodelssupportthesamesuperengineandthesameinterfacemodule,whichprotectstheuser'sinvestment.Themainfeaturesofthisseriesinclude:
Highportdensity.Itsupportsupto38410/100BaseTxadaptiveEthernetports,192100BaseFXfiberopticfastEthernetports,and130GigabitEthernetports(GBICslots).
Fastspeed.TheswitchingbackplaneofC6500canbeexpandedto256Gbps,andthemulti-layerswitchingspeedcanbeexpandedto150Mpps.TheC6000'sswitchingbackplanebandwidthis32Gbps,andthemulti-layerswitchingrateis30Mpps.Supportupto8Fast/GigabitEthernetportsusingEthernetchanneltechnology(FastEtherChannel,FECorGigabitEtherChannel,GEC)toconnect,logicallyachieveaportrateof16Gbps,andcanalsoachieveportaggregationacrossmodules.
Multilayerexchange.Themulti-layerswitchingmoduleoftheC6000seriescanperformwire-speedIP,IPXandIP-multicastrouting.
Goodfaulttoleranceperformance.TheC6000seriesisequippedwithredundantsuperengines,redundantloadbalancingpowersupplies,redundantfans,redundantsystemclocks,redundantuplinks,andredundantswitchingbackplanes(onlyfortheC6500series)toachievehighsystemavailability.
Richsoftwarefeatures.C6000softwaresupportsawealthofprotocols,includingNetFlow,VTP(VLANTrunkingProtocol),VQP(VLANQueryProtocol),ISLTrunking,HSRP(HotStandbyRouterProtocol),PortSecurity,TACACS,CGMP(CiscoGroupManagementProtocol),IGMP,etc.Wait.
SanwangSwitch
MACtable,flooding,forwarding
Q1:Whatdoestheswitchdo?
Answer:Theswitchdoesthreethings:forwardsthedatapacket,floodsthedatapacket,anddiscoversthenewMACaddress.
Q2:WhatdoestheMACtabledo?Howisitgeneratedandused?
Answer:1)MACtableislikephonebook(yellowpage),phonebookrecord(name,phonenumber),MACtablerecord(MAC,interface).2)Whentheswitchreceivesadatapacket,itsearchestheMACtablewithitsMACdestinationaddress.Datapacketsareforwardedwhentheyarefound,andfloodedwhentheyarenotfound.3)Whenreceivingadatapacket,theswitchusesitssourceMACaddresstoquerytheMACtable.Ifitdoesnotfindit,ithasfoundanewaddressandaddsthisaddressandtheinputinterfacetotheMACtable.Inthisway,theMACtablegraduallygrowswiththenewdataflow,andthegeneratedentry(MAC,Interface)canbeusedtoforwardthedatapacket.
Q3:Whyshouldtheswitchflood?
Answer:Thenetworkisoftenfloodedtofindthings.Thecharacteristicsofthelocalnetworkarebroadcastingandflooding.Theswitchisalocalnetworkdevice,whichisconvenientandefficientforflooding.TheswitchusestheMACtabletoforwarddatapackets.IfthereisnodestinationMACinthetable,itcannotforwardandusesfloodinginstead.Withoutknowingtheswitchingpath,floodingcanquicklydeliverthedatapackettothedestination.Atthesametime,thesideeffectsoffloodingalsohavedifferentmeanstocontrol.
Q4:WillthesameMACbeinputfromdifferentinterfaces?Howtodealwiththeswitch?
Answer:Yes.However,onlyoneMACisreservedintheMACtable.Forexample,MAC1isenteredfromF0/1forthefirsttime,andanewentry(MAC1,F0/1)isaddedtotheMACtable.Later,MAC1isinputfromanotherinterfaceF0/5.Thistime,insteadofaddinganewentryintheMACtable,itupdates(MAC1,F0/1)to(MAC1,F0/5).
QFive:UnderwhatcircumstanceswillthesameMACbeinputfromdifferentinterfaces?
Answer:Loop.Forexample,S1,S2,S3areconnectedtoformatriangle,H1isconnectedtoS1,andH2isconnectedtoS2,causingfloodingonthenextthreeswitches.Forexample,H1pingH2,theMACtableisempty,S2willfindthatpingcomesfromtwodifferentinputinterfaces.
Q6:IstheentryintheMACtableoftheswitchaging?
Answer:Yes,about5minutes.TheMACtableonlystoresthemoreactiveMACs.Iftheswitchdoesnotreceiveadatapacketfromanodewithinafewminutes,theswitchwillcleartheMACofthisnodefromtheMACtable..
Q7:HowmanyMACscanbeplacedintheMACtableofaswitch?Answer:Itdependsonthemodelandprice,from4Kto1M(1024K).
Quicklysolvetheswitchfailure
InordertoimprovetheoperationandmaintenanceefficiencyoftheLAN,weneedtoaccumulatevariousswitchtroubleshootingexperienceinpeacetime,sothatwhenweencounterafailure,wecanquicklysolvetheswitchfailure.
It’stroublesometoresettheVLAN
Whenmanagingandmaintainingtheunit’slocalareanetwork,ifthecascadeportconnectedtotheordinaryswitchischanged,thendividetheVLANsetintheswitchsystembeforeItoftenfailstofunctionproperly.Inthiscase,doweonlyhavetore-divideandsetupVLANs?Ifthisisthecase,thenetworkmaintenanceworkloadisobviouslyverylarge;infact,afterchangingthecascadingportsofordinaryswitches,weonlyneedtoenterthebackgroundmanagementinterfaceoftheswitch,ModifytheworkingmodeofthecascadeportsothatallVLANaccesscanpass,sothatyoucanavoidresettingtheVLANoperation.Nowwetakethelocalareanetworkofacertainunitasanexampletointroducetoyouthespecificsettingstepsoftheswitch:
Assumingthatthereare6VLANsinthelocalareanetworkoftheunit,theS1switchislocatedintheAsubnet,andtheS2switchLocatedintheBsubnet;theunithaspurchasedseveralnewworkstationsthesedays,andnowitisnecessarytomovetheS1switchtotheBsubnet,whilethepreviousS1switchwasdirectlyconnectedtothecoreswitchoftheunit’slocalareanetworkwithanopticalfibercableonport24of.Inordertoavoidre-dividingVLANsintheswitchsystem,wecanchangetheportworkingmodeofS1andS2switches.Forexample,wecanfirstchecktheportsettingsoftheS1switch;inthischeck,wecanlogintothebackgroundmanagementinterfaceoftheswitchthroughthetelnetcommandandexecutethestringcommand"displayinterfaces",sothatwecancheckThespecificconfigurationofeachportoftheswitchisup.Fromtheresultsreturnedbytheabovecommand,wecanseethatthestatusofport26oftheS1switchthatmaintainsacascadingrelationshipwiththeS2switchis"interfaceethernet0/26,portaccessvlan2".Throughthisstatus,itisnotdifficulttounderstandthattheS1switchonlybelongstoVLAN2.Thatistosay,theswitchonlyallowstheworkstationsinVLAN2topass,andtheworkstationsinotherVLANscannotpass;whentheS1switchchangesitsposition,itwilldefinitelybelocatedinthenewVLAN,inordertomakealltheworkstationsinthenewVLANpass.Passable,weneedtochangethe26-portworkingmodeoftheS1switchto"trunk"here,sothattheS1switchdoesnotneedtore-divideandsetupVLANs,sothatallworkstationsinthenewVLANcanpass.
MaybemanyusersmaywonderwhytheS1switchcancommunicatenormallywiththeunit’sLANnetworkbefore?TheoriginalS1switchwasconnectedtotheunitcoreswitchthroughafiberopticcablebefore,andthefiberconnectionportTheworkingmodehasbeensetto"trunk".WhentheplacementoftheS1switchischanged,sincenofiberopticcableisusedtoconnecttheswitch,thecorrespondingfiberconnectionportisuseless.
Whenmodifyingthe26-portworkingmodeoftheS1switch,wecanfirstremotelylogintothebackgroundmanagementinterfaceoftheswitch,andexecutethestringcommand"system"inthecommandlineoftheinterfacetosettheS1switchSwitchtothesystemconfigurationstate,andthenexecutethe"interfaceethernet0/26"commandtoentertheconfigurationstateoftheNo.26connectionportoftheS1switch,andthenenterthestringcommand"portlink-typetrunk"inthisstate,andclickAfterpressingtheEnterkey,theworkingmodeoftheNo.26connectionportoftheS1switchissuccessfullymodifiedtothe"trunk"type;inordertoallowallVLANsintheLANtoaccesstheS1switchthroughthisport,wealsoneedtoexecutethestringcommand"port"Trunkpermitvlanall",inordertospecifytheconnectionportNo.26toallowaccessfromworkstationsinallVLANs.Followingthesameoperation,wecanmodifythecascadingportworkingmodeoftheS2switchtoensurethatallworkstationsintheLANcanaccesstheS2switch.
Thehostcannotbepingedthrough.
Whenmanagingandmaintainingthenetwork,weoftenperformaPingcommandtestontheswitchofahost’sIPaddressintheLAN.Duringthetest,WhenencounteringtheproblemthattheIPaddressofthetargethostcannotbepinged,howshouldweeliminateit?Afterconfirmingthatthetargethosthasbeenpoweredonandthesystemitselfisworkingproperly,wecanperformthefollowingintheswitchTroubleshootoperation:
First,logintothebackgroundmanagementinterfaceofthetargetswitchthroughthetelnetcommand,executethestringcommand"displayinterfaces"inthecommandlineoftheinterface,andlookatthetargethostintheresultinterfacethatpopsuplaterWhethertheIPaddressoftheportconnectedtothelocalswitchisinthesamenetworksegment,orcheckwhethertheworkingmodeofthedesignatedconnectionportofthelocalswitchis"trunk"type,iftheseparametersaresetincorrectly,wemustmodifythemintime.
Next,executethestringcommand"displayarp"andcarefullycheckfromthepop-upresultinterfacewhetherthecontentsoftheARPtablemanagedandmaintainedbythelocalswitcharesetcorrectly.Onceanincorrectrecordorentryisfound,itmustbepromptlychangedItismodified.
Next,checkwhichvirtualsubnetthecommunicationportofthelocalswitchconnectstothetargethostisin.Afterfindingthecorrespondingvirtualsubnet,checkwhethertheVLANcommunicationinterfaceiscorrectlyconfiguredforthevirtualsubnet.IfithasbeenconfiguredIfso,wemightaswellcheckwhethertheIPaddressoftheVLANcommunicationinterfaceisinthesameworkingsubnetastheIPaddressofthetargethost.Iftheconfigurationisfoundtobeincorrect,itmustbemodifiedintime.
IftheaboveconfigurationparametersarenormalandthelocalswitchcannotpingthetargethostaddressintheLAN,thenwemightaswellenabletheARPdebuggingswitchinthelocalswitchsystemtocheckthelocalWhethertheswitchcansendandreceiveARPpacketscorrectly,ifthelocalswitchcanonlysendARPpacketstotheoutsidebutcannotreceiveARPpacketsfromtheoutside,thecauseofthefailureisprobablyatthephysicallinklayeroftheEthernet.Atthispoint,weneedtofocusoncheckingthephysicallinklayer.
FailuretoforwardIPpackets
IfthelinklayerprotocolstatusoftheinterfaceofthelocalswitchandthephysicalstatusoftheinterfacearealldisplayedasUP,theswitchcannotforwardIPdatagramsnormallyAtthetimeofthisarticle,itismostlybecausethespecifiedprotocolofthelocalswitchfoundthattheroutingparameterswerenotsetcorrectly,orthestaticrouteofthelocalswitchwasnotsettotakeeffect.Atthispoint,wecanusethetelnetcommandtoremotelylogintothebackgroundmanagementinterfaceofthetargetswitch,andenterthecommandlinestate,enterthestringcommand"displayiprouting-tableprotocolstatic",clicktheEnterkeyandthencheckwhetherthelocalswitchiscorrectConfigurestaticrouting.Ifthereisnoconfiguration,youneedtoreconfigureitintime;
Afterconfirmingthattheaboveconfigurationiscorrect,executethestringcommand"displayiprouting-table"tocheckwhetherthelocalstaticroutingissetIttakeseffect.Ifitdoesnottakeeffect,youneedtore-enableandsetupthestaticroute.Inthisway,theproblemthatIPpacketscannotbeforwardedcanbesolved.
Seriousdatapacketlossfailure
Thenetworkadministratorfirsttriedtoconnecttheincominglineofthehubdirectlytothefaultyworkstation,andthenexecutedthepingcommandtestontheserver.ThetestresultfoundthatnodataappearedPacketdelayphenomenon,thereisnodatapacketdropphenomenon,thetestresultisnormal.Thenthenetworkadministratorperformedapingcommandtestoperationontheoldcomputerwiththe10Mnetworkcardinstalled.Thetestresultturnedouttobenormal,andthemalfunctioningcomputerhappenedtobesomenewworkstationswiththe100Mnetworkcardinstalled.Thenetworkadministratorhasrepeatedlyanalyzedthisphenomenon.Isitpossiblethatthetransmissionspeedofthenetworkcardoftheworkstationandthetransmissionspeedoftheswitchhaveamatchingproblem?Thinkingofthis,thenetworkadministratorthentransferredthe100Mnetworkcardequipmenttothosefaultycomputers.Thespeedwasforciblyadjustedto10M,andthentheaccesstestwascarriedout,anditwasfoundthatthefailurephenomenonwasnotthere.Obviously,theabovefailurewasindeedcausedbythespeedmismatch.Inthefuture,whenweencounterthesamefailurephenomenon,wemaywishtocarefullycheckwhetherthetransmissionspeedofthefaultyworkstationandtheswitchmatch.Ifitdoesnotmatch,weonlyneedtoforciblymodifythetransmissionspeedofthenetworkcarddeviceinthefaultyworkstationtoensurethenetworkcarddeviceandtheswitch.Theworkingspeedremainsmatched.