DUT-Chapter5-swtich(大連理工軟件學(xué)院計(jì)算機(jī)網(wǎng)絡(luò)課件)

Chapter5switchingLocalAreaNetworkInordertoensurethatthesenderandthereceivercancoordinatewitheachother,anumberofstandardizationorganizationspromotethedevelopmentofcommunicationstandards.LocalAreaNetworkANSIAmericanNationalStandardInstituteANSIdesignedaSCIIcodeset.Itisawidelyusedcommunicationsstandardcode.ITU:InternationalTelecommunicationUnionITUhasthreemaindepartments:WirelessCommunicationDepartment(ITU-R),TelecommunicationStandardization(ITU-T),DevelopmentDepartment(ITU-D).1953-1993,ITU-TisknownasCCITT(InternationalTelegraphandTelephoneConsultativeCommittee).BothITU-TandCCITTputforwardrecommendationsinthefieldoftelephoneanddatacommunications.WeoftenencountermanyCCITTrecommendations,suchasCCITT'sX.25,althoughsince1993theseproposalsaremarkedwiththeITU-Tmark.LocalAreaNetworkEIA:

ElectronicIndustriesAssociationEIAisanAmericanelectroniccompaniesorganizations,suchas:RS-232interface,thiscommunicationinterfaceallowsdataexchangebetweendevices.IEEE:

InstituteofElectricalandElectronicsEngineersIEEEsetsstandardsfortheelectronicsindustry.IEEEisdividedintoanumberofstandardsorganizations(orworkinggroup),andeachworkinggroupisresponsibleforanareaofstandards.Theworkinggroup802setsnetworkequipmentsandhowtocommunicatewitheachother'sstandards.ISO:

InternationalStandardOrganizationLocalAreaNetwork5.1DefinitionofLANswitchingLANswitchingtechnologyisbasicallysimilartothebridge,buttheexchangeoftwolayerisbasedonthebridgeconnectionofthehardware,inwhichtheframeishandledbythespecialhardware(ASIC:Application-specificIntegratedCircuit).LocalAreaNetwork5.1DefinitionofLANswitchingComparisonofswitchesandhubsTaskhierarchiesaredifferent.Hubforwardsthepackettoallports;Fortheswitch,thedestinationaddressesaredifferentacrossbroadcast,multicast,unicast.Similarwiththebridge,forexample,itistransparentforthenetworklayer.LocalAreaNetworkLANextensionwithhubsAdvantages:EnabledifferentcomputersontheLANoforiginalcollisiondomainstocommunicateacrossthecollisiondomain.Expandthegeographicscopeoflocalareanetworkcoverage.Disadvantages:Collisiondomainincreases,butthetotalthroughputdoesnotincrease.Ifdifferentcollisiondomainsusedifferentdatarates,thenthehubcannotbeusedtointerconnectthem.LocalAreaNetworkLANextensioninthedatalinklayerNetworkBridgeisusedtoextendLANinthedatalinklayer.Bridgeworksinthedatalinklayer,whichforwardsthereceivedframeaccordingtothedestinationaddressofMACframe.Framebridgehasthefunctionoffilteringanddevelopingaspecificpath.LocalAreaNetwork5.2SwitchesClassificationoftheswitchaccordingtoarchitecture:SingledesktopswitchesHeapbattlementswitchesModularswitchesLocalAreaNetwork5.2SwitchesSwitchesareconnectedphysicallyandlogicallythroughaspecificbusLocalAreaNetwork5.2SwitchesModularswitchesLocalAreaNetwork5.2SwitchesAccordingtothelocationinthenetworkAccesslayerswitchAggregationlayerswitchCorelayerswitchAccordingtothefunctionThreelayersswitch(alsoknownasroutingswitch)TwolayersswitchLocalAreaNetwork5.2SwitchesLocalAreaNetwork5.3ForwardingandfilteringdataframesDataframesforwardingofswitchesmustmeetfollowingconditions:1)Meettheaddressingprovisions2)Provide:When48-bitgeneral-purposemanagementaddressdoesn’tsupport,groupMACaddressisassignedtoidentifythebridgeprotocolentity.Portidentifierintherealizationofspanningtreealgorithmandprotocolidentifieseachportintheswitch.LocalAreaNetwork5.3ForwardingandfilteringdataframesFramesforwardedbyswitches1)Providethecapacityofcontrollingtheprioritymappinginforwarding.2)Provideavarietyoftrafficclassifications.3)ProvidethebehaviorofforwardingofindependentMACaddress.4)Managetheprioritiesofframestransmitted.LocalAreaNetwork5.3ForwardingandfilteringdataframesTheforwardingofdataframescanbaseonStore-andForwardandDirectForward.TheswitchmustsupportStore-andForward.TheswitchcansupportDirectForward.TheswitchsupportingDirectForwardmustbesettothedefaultStore-andforward.LocalAreaNetwork5.3ForwardingandfilteringdataframesFilterframeThedataframesfilteringoftheswitchmustbeconsistent:ItAchievesbasicfilteringservice,andforeachport,asingleTrafficClassisassociatedwith.Thefollowingparametersinfilteringdatabaseusethevaluesspecified.Sizeoffilteringdatabase,thelargestnumberofentriesthatthefilterdatabasecanaccommodate.Sizeofpermanentdatabasesize,thelargestnumberofentriesthatthepermanentdatabasecanaccommodate.LocalAreaNetwork5.3ForwardingandfilteringdataframesDataframesfilteredbytheswitchProvidethecapacityofreadingandupdatingthefilteringdatabaseandthepermanentdatabase.Providethecapacityofsettingtheupdate-timeofthefilterdatabase.Switchessupportingthisabilityshouldimplementalloptionalvaluesspecifiedbythestandard.ProvidethebehavioroffilteringofindependentMACaddress.LocalAreaNetwork5.3ForwardingandfilteringdataframesNote:TheagingtimeofforwardingandfiltersmustbeinMactable(5minutes).Tocontroltheforwardingrange,thevlan

stpcouldbeintroduced.Vlan:ForwardingpacketsinvirtualLANStp:Becausetheporthasadifferentstatus,someportsdonotallowforwardingpackets.LocalAreaNetwork5.4TechnicalproblemsAuto-negotiationAuto-negotiationallowsanetworkequipmenttosendthemessageofworkmodesupportedtotheoppositeside,andacceptthecorrespondinginformationdeliveredfromtheoppositeside.Thetwosidesnegotiateaoptimalportworkmodesupportedbybothofthemtocommunicate.LocalAreaNetwork5.4TechnicalproblemsAuto-negotiation(1)DetectLinkstatusDeterminewhethertheindicatorlightornotbyreadingphy

(2)Duplex:halfandfull-duplexoperation(3)FlowControlforfull-duplex

DA=01-80-C2-00-00-01andtype=88-08(pause)(4)SpeedLocalAreaNetworkLocalAreaNetworkLocalAreaNetworkLocalAreaNetworkLocalAreaNetworklearningandForwardingLearningprocessTheindexofpacketismainlySA(sourceaddress).MACTableissearchedtofindifthereisrelevantinformation.Ifitexists,theprocessofexchangeiscarriedout.Otherwise,therelevantinformationsuchasSA,PORT,etc,arewrittenintheMACTable.SothatthereisanewtableentryintheMACTable.LocalAreaNetworkForwardingprocessTheindexofForwardingismainlybasedonDA(destinationaddress).IfthecorrespondingrecordcanbefoundintheMACtable,thenthepackageisforwardedtothespecificportinthevlantable.Otherwise,thepackageisbroadcastedasabroadcastpackage.Thisimpliesthatallportsoftheswitchshouldreceivethispackage.LocalAreaNetworkNoteAlltableentriesintheMactablehaveagingtime.Ifthesecondrepetitivelearningcan’tbecarriedoutwithinagingtime,thenthistableentryshouldbedeletedinagingtime.LocalAreaNetworkSpecificalgorithmSupposethattheframe(src=x,dst=y)reachestheportNofBridgeBridgesearchestheforwardingtableIfthetableentry<x,N,Age>isfound,thenUpdateAgetothecurrenttimeOtherwiseInsertthenewtableentry<x,N,currenttime>DeletethetableentrieswhoseAgesaretimeout.LocalAreaNetworkLocalAreaNetworkLocalAreaNetworkFlowcontrolCurrentlyused:rate-basedflowcontrolFull-duplexflowcontrol(IEEE802.3hasthefollowingprovisions)A，pause

controlPauseframe

DA=01-80-C2-00-00-01andtype=88-08(pause)Itisusedtopreventthesidetoreducetheframesendingratewithinacertaintimeorstopforsometimetosend.LocalAreaNetworkVirtualLAN(VLAN)LocalAreaNetworkTheconceptofvirtualLANVirtuallocalareanetwork(VLAN)isconstitutedbyanumberofLANsegmentsandlogicgroupsthatareindependentofthephysicallocation.Thesesegmentshavesomecommonneeds.EachframehasaspecificVLANidentifier.TheidentifierspecifieswhichVLANdoestheworkstationthatsendsthisframebelongto.VirtualLANisonlytheLANprovidingaservicetousers,ratherthananewlocalareanetwork.LocalAreaNetworkReasonsforusingVLANLocalAreaNetwork……broadcastBroadcastdomainandbroadcaststormTheswitchnetworkformsabroadcastdomainReasonsforusingVLANLocalAreaNetwork……broadcastrouterItiscostlytouserouterstoisolatebroadcastdomainsReasonsforusingVLANLocalAreaNetworkBroadcastdomain1VLAN10Broadcastdomain2VLAN20Broadcastdomain3VLAN30MarketingDepartmentEngineering

DepartmentFinanceDepartmentItislowcosttouseVLANtoisolatebroadcastdomainsReasonsforusingVLANAllEthernetpacketssuchaspacketsofunicast,multicast,broadcastandunknownareonlytransmittedinVLAN.Controltheinternetstorm.Itcanchangethenetworktopology.ThemainpurposeofsettingVLANistorestrictthescopeofbroadcastpacketsandreducetheeffectofbroadcastpackets,soastoImprovenetworksecurity.LocalAreaNetworkPhysicalnetworksegment:vlanLogicalnetworksegment:ipLocalAreaNetworkLocalAreaNetworkEthernetSwitchA4B1EthernetSwitchVLAN3C3B3VLAN1VLAN2C1A2A1A3C2B2EthernetSwitchEthernetSwitchThecompositionofthreevirtuallocalareanetworksVLAN1,VLAN2

andVLAN3LocalAreaNetworkEthernetSwitchA4B1EthernetSwitchVLAN3C3B3VLAN1VLAN2C1A2A1A3C2B2EthernetSwitchEthernetSwitchThecompositionofthreevirtuallocalareanetworksVLAN1,VLAN2

andVLAN3WhenB1sendsdatatothememberofworkinggroupVLAN2,workstationB2and

B3willreceivetheinformationbroadcasted.LocalAreaNetworkEthernetSwitchA4B1EthernetSwitchVLAN3C3B3VLAN1VLAN2C1A2A1A3C2B2EthernetSwitchEthernetSwitchThecompositionofthreevirtuallocalareanetworksVLAN1,VLAN2

andVLAN3WhenB1sendsdata,workstationA1,A2and

C1willnotacceptthetheinformationbroadcastedbyB1.LocalAreaNetworkEthernetSwitchA4B1EthernetSwitchVLAN3C3B3VLAN1VLAN2C1A2A1A3C2B2EthernetSwitchEthernetSwitchThecompositionofthreevirtuallocalareanetworksVLAN1,VLAN2

andVLAN3Virtuallocalareanetworkrestrictsthenumberofworkstationstoreceivebroadcastinformation.Itmakesthenetworkwillnotbroadcasttoomuchinformation(thatis,"broadcaststorm")tocausedeterioration.VLANclassificationPort-basedVLANMACaddressbasedVLANProtocol-basedVLANSubnet-basedVLANLocalAreaNetworkVLANbasedonMACaddressSwitchsupportsupto12entries.SwitchportsdetermineVLANbelongingaccordingtothedeviceMACaddressconnectingtotheport.althoughthephysicallocationofthesitehaschanged,itstillbelongstotheoriginalVLAN.Itisconvenienceandflexibilityformobileusers.LocalAreaNetworkLocalAreaNetworkVLANbasedonMACaddressLocalAreaNetwork

VLANbasedonportVLANbasedonportItisastaticVLAN.Vlanisdesignedastheports.AVLANcanspanmultipleswitches.AswitchportcanbelongtoseveraldifferentVLAN,calledthepublicport.Ifaportbelongstoacertainport,allsitesconnectingtotheportwillbecomethesamevlan.0-4095vlanentrieswillbesupported.LocalAreaNetworkVLANbasedonprotocolLocalAreaNetworkVLAN

TableTypeVLANIPXprotocolIPprotocol……VLAN5VLAN10……HostAHostBHostCHostDEthernetswitchUsingtheIPXprotocolRunningIPprotocolUsingtheIPXprotocolRunningIPprotocolVLANbasedonsubnetLocalAreaNetworkVLANTableIP

NetworkVLANIP/24IP/24……VLAN5VLAN10……HostAHostBHostCHostDEthernetswitch89VLANstandard:IEEE802.1QOverviewVLANframeformatVLANlinktypeVLANframeforwardingalgorithmLocalAreaNetworkIEEE802.1QOverviewLocalAreaNetworkIEEE802.1Qcanbefreedownloadedfrom

IEEE802.1QtagEthernetcodetagformatLocalAreaNetworkDestinationMAC

address

6bytesSourceMACaddress

6bytesData/Fill46~1500bytesFCS4bytesTPID2bytesTCI2bytes

2bytes加入的VLAN頭0123456701234567User-priorityTokenRingEncapsulationFlag(TR-encap)0123456701234567VLANIdentifier(VID)

VType(0x8100)1000000100000000vid（1）802.1Qtype

2bytes（2）UserPriority

3bit（3）CFIThestandardformatindicatorrepresentsthe followingarehexadecimalnumbers

（4）VID12bitSupplementIEEE802.1QissupportedSwitchesofIEEE802.1QarenotsupportedBothofthemsupportthevlan,butthelattercannotreadIEEE802.1QEthernetframe.LocalAreaNetworkPVID/VIDImportantConceptsPort-basedVLAN'sID(PortVLANIDnumbers,abbreviatedPVID)VLAN'sID(VLANIDnumbers,abbreviatedasVID)PVIDdefinestheswitchforwardsdatapacketstowhichVLAN,andwhenthepacketwillbeforwardedtoanotherswitchport,orsomewhereinthenetwork.Eachporthasonlyonepvid.LocalAreaNetworkPVID/VIDImportantConceptsVid,thenumberofpacketsinthenetworkreceivedoverVLAN.AportbelongstomultipleVLAN(VIDs)PVIDandVID,twovariablesareusedtocontrolcapabilitiesoftheportsendingandreceivingVLANdatastreams,andthedifferencebetweenthemisthatthelatterallowstheinformationcanbesharedbymultipleVLAN.LocalAreaNetwork802.1QVLANsegmentForexample,thedatapacketisfromPort12,pvid=2,thenthepacketwillbedisseminatedinvid=?.Thedestinationaddressisintheotherport10,anditspvid=?Vid=?Ifvid=?etc,thepacketwillbetransmittedtothedestinationaddress.LocalAreaNetworkLocalAreaNetworkfunction？Vlantable？LocalAreaNetworkInthepictureabove,therearethreedifferentVLAN,eachportaccordingtotheirportVLANID(PVID)tosendpacketsintheirownVLAN.However,thereisaporttoreceivealltheVLANpackets.Thesettingasfollows:Serverconnectedtoport7,itcanbesharedbyVLAN1,2,3,sotheport7canreceivepacketsfromVLAN1,2,andallports(client)couldsendthedatapackettoport7.Ports1,2and3inVLAN1(theirPVID=1)sendpacketstoit,whiletheports11and12inVLAN2(theirPVID=2)sendpacketstoit.ServerusesthethirdVLAN(PVID=3)tosendfilesrequestedbycomputersinVLAN1andVLAN2.LocalAreaNetworkVLANsSpanningMultipleSwitches802.1QVLANcanbesetbetweenmultipleswitches.InthesettingofthisVLAN,youneedtopayattentiontotwopoints:WhethertheseswitchessupportIEEE802.1Q(IEEE802.1Q-compliant).ThepacketofVLANisrequiredtoaddtags(tagged)orremovetags(untagged).LocalAreaNetworkTaggingTheoperationadding802.1QVLANinformationintothepacketheader.Theportthathastheabilitytoenabletagging(taggingenabled)willaddPVID,priorityandotherVLANinformationintoalldatapacketsincomingandoutgoingthroughtheport.LocalAreaNetworkTaggingIfthepackethasbeentaggedpreviously,thentheportwillnotchangethedatapackets,allowingittomaintaintheirexistingVLANinformation.Tag(Tagging)allowsdatapacketstobetransferredfromaswitchsupporting802.1Qtoanothersimilarswitch.802.1QframeLocalAreaNetworkUntaggingTheoperationremoving802.1QVLANinformationfromthepacketheader.Theportthathastheabilitytoenableuntagging(untaggingenabled)willremovePVID,priorityandotherVLANinformationformheadersofalldatapacketsincomingandoutgoingthroughtheport.802.3frameLocalAreaNetworkUntaggingIfthepackethasn’tbeentaggedpreviously,thentheportwillnotchangethedatapackets.Tag(Tagging)allowsdatapacketstobetransferredfromaswitchsupporting802.1Qtotheswitchnotsupporting802.1Q.LocalAreaNetworkIngressportIftheingressportontheIngressFilterissettoenabled,thentheswitchwillcheckeverypacketpassingthroughtodeterminewhetheritisamemberofthesameVLANtodecidewhethertoforwardthepacket.Ifselfport(ingressport)isamemberofVLANtagging,thenthepacketwillbeforwarded.Otherwise,discardthepacket.LocalAreaNetworkIngressportIfIngressfilteringissettodisabled,thentheswitchwillhandleallpacketsreceivedbyinboundportwiththeconventionalway.Implementation:pvidbelongstothevlaninthetagLocalAreaNetworkEgressport

Iftheegressportisconnectedtoaswitchsupporting802.1Q,thentagsmustbeaddedtothedatapacketssothatotherswitchcandeterminewhetherforwardingthepacketaccordingtothetags.Iftheegressportisconnectedtoaswitchnotsupporting802.1Qoraworkstation,thenthetaginthepacketwillberemoved,andthepacketbecomestoaEthernetdatapacketsothatthedevicescanreadthispacket.LocalAreaNetworkVLANbasedon802.1QWhentheswitchmaintainstheVLANbasedon802.1Q,taggingisneeded.Theoperationoftaggingcanaddtheinformationof802.1QVLANintotheheaderofeachpacket.LocalAreaNetworkVLANbasedon802.1QAccordingthetaginformationreceived,theswitchsupporting802.1QcanmaintaintheintegrityofVLAN,andforwardpacketsbasedonitspriority,andsoonTheprincipleofthedatatransferbetweentheswitchsupporting802.1Qandtheswitchnotsupportingasfollows:LocalAreaNetworkThinkingQuestionsEquipments:3pcasclient,2serverasswitchDemands:Pc1invlan1communicateswiththeserver1Pc2,3invlan2communicatewiththeserver2pcandtheserverareindifferentphysicallocations.Drawthenetworkdiagram?SetPvid

vidtag/untag.LocalAreaNetworkLocalAreaNetworkBasiclearningstrategiesItisconsistentwithlearningstrategiesofthetransparentbridgegeneralbasically.Thedifferencesare:Therelationofmactableandthenumberofvlanisone-to-onecorrespondence.Learningsourcemac+vidLocalAreaNetworkBasicforwardingstrategiesIfthemacframeincomingisuntaggedorvid=0,pvidisaddedintothisframe.Notonlyaccordingtothedestinationaddressofthemacframetofindtheoutputportnumber.Itistodeterminetheoutputportbymacandvidofthedestination.Whenoutputtingthepacketfromthedestinationport,itisneedtodecidewhetherstrippingvidfromthemacframeaccordingtountagedortagged.LocalAreaNetworkSTPThoughtEnableallswitchestocommunicatewitheachother.UsingaspanningtreeconnectingwitheachLANtocovertheactualtopology.LocalAreaNetworkSpanningTreeAlgorithmLocalAreaNetworkFFFFFFFReasonsoftheintroductionofSpanningTreeProtocolLocalAreaNetworkByblockingredundantlinkstoeliminatethepathloopthatmayexistinthebridgenetwork.Whenthepathcurrentactivatedfails,itcanrestorenetworkconnectivitybyactivatingredundantback-uplinks.ROOTLANALANBLANCLANDLANEPrinciple

twostandards:802.1D、802.1wBPDU(Bridgeprotocoldataunit)Whenthereisaloop,theswitchwillselectalinktotransferdatabyusingspanningtreealgorithm,andsetthestateofrelatedportsasblockingtobroketheotherlinkvirtually.Oncethelinkcurrentlybeingusedcrashes,atreewillbebuiltagain.LocalAreaNetworkRootBridgeThebridgewiththeminimumIdistherootbridge.RootPortThebridgeselectstheportwiththeminimumcosttotherootbridgeistherootport.Whentherearemultipleports,theportwiththeminimumIDistherootport.LocalAreaNetworkSomeconcepts:DesignatedPort/BridgeForeachLANsegment,abridgeischosenasitsdesignatedbridge.Thestandardisthatthepathcostfromthedesignatedbridgetotherootbridgeislowest.TheportoftheLANsegmentconnectingtothedesignatedbridgeisthedesignatedportofthisLANsegment.Whentherearemultipleports,theportwiththeminIDisthedesignatedport.PathCostThecostofMACframeistransferredthroughtheporttoacertainLAN.Rootpathcost:Foranybridge,thepathcostisfromtherootporttotherootbridgeLocalAreaNetworkLocalAreaNetworkInthesamenetwork(broadcastdomain-wide),aswitchisselectedastherootbridge(Root).Ineachnon-rootbridge,therootportisselected(RootPort).Ineachsegment,thedesignatedportisselected.otherPortsareblocked.HowSTPworks?EachbridgeinitiallyassumestobeRoot(RootPathCost=0)ElectasingleRootbridge(smallestID)CalculateshortestpathfromthemselvestotheRootbridgechoosetheRootport(shortestpathtoRootbridge)ForeachbridgeElectaDesignatedBridgeforeachLANastheoneclosesttotheRootbridgeSelecttheportstobeDesignated

Allotherportsarebackup/alternated(notforwardingstate)inblockedstate.LocalAreaNetworkConfigurecontentsofthemessageConfigurationinformationisalsocalledbridgeprotocoldataunit(BPDU)ThemaincontentsincludeIdentifieroftherootbridge(RootID).Theminimumpathcostfromthedesignatedbridgetotherootbridge(RootPathCost).Identifierofthedesignatedbridge.Identifierofthedesignatedportofthedesignatedbridge.Inaword:RootID，RootPathCost，DesignatedBridgeID，DesignatedPortIDLocalAreaNetworkLocalAreaNetworkDMALLCHeaderSMAL/TPayloadDMA:DestinationMACaddressThedestinationaddressofconfigurationmessageisafixedmulticastaddressofbridge(0x0180c2000000).SMA:SourceMACaddressTheMACaddressofthebridgesendingthisconfigurationmessage.L/T:framesizeLLCHeader:FixedlinkheaderofconfigurationmessagePayload:BPDU

dataValueDomainByteProtocolID2ProtocolversionBPDU

TypeFlagBitRootbridgeIDPathCost開銷DesignatedBridgeIDDesignatedportIDMessageAge11184822MaxAgeHelloTimeForwardDelay222BPDUexchangeLocalAreaNetworkEachbridgeperiodicallysendsthefollowingBPDUtotheLANconnectingwithit.rootbridge(whatthesenderthinksitis)rootpathcostforsendingbridge

Identifiessendingbridge

IdentifiesthesendingportrootIDcostbridgeIDportIDInitializationInthebeginningoftheprotocol,eachbridgeregardsitselfasRootBridge.SoeachBridgesendstheBPDUasthefollowingformtotheLANconnectingwithit.LocalAreaNetworkB0BPComparisonofBPDULocalAreaNetworkGiven

twoBPDUsM1andM2：IDR1C1IDB1M1M2IDP1IDR2C2IDB2IDP2Wesaid

M1isbetterthanM2,if(R1<R2), Or(R1==R2)and(C1<C2), Or(R1==R2)and(C1==C2)and(B1<B2), Or(R1==R2)and(C1==C2)and(B1==B2)and(P1<P2)UpdateBPDULocalAreaNetworkR1C1B1P1M1R2C2B2P2M2Then

BridgeBupdatesitsownBPDUasfollowing:R2C2+1B1P1EachBridgecomparesallBPDUsreceivedbyittotheBPDUsentbyitself.IfBridgeBsendsaBPDUM1asfollowing:ReceivesabetterBPDUM2:ConfigurationinformationhandlingIfitisrootbridge,thentheshortestpathcostis0,otherwise,itisthesummationofRootPathCostoftheoptimalconfigurationinformationandthecostoftheportreceivingthisconfigurationinformation.LocalAreaNetworkTheconstructionofthetreeAfterdeterminingRootPortandDesignatedPort,eachBridgeconsiders:RootPortsareinthespanningtree,whichareforwardingstate.DesignatedPortsareinthespanningtree,whichisforwardingstate.Allotherportsaren’tinthespanningtree,whichareblockedstate.LocalAreaNetworkAnexampleforacceptanceandprocessofconfigurationinformation

LocalAreaNetworkAccordingtothepriorityoftheconfigurationinformationreceived,Port4isselectedastherootport,Port1andPort2asthedesignatedports,Port3andPort5areblocked.TheconfigurationinformationsentfromPort1andPort2:(23,15,81)WhereRootId=23RootPathCost=14+1=15RootPort=Port4Port1Port2Port3Port4Port5blockingblocking32，0，3232，18，12323，14，32123，14，10023，15，80root23，15，81B8123，15，81HowtodealwithlinkfailureHelloTimeBridgesendstheconfigurationinformationperiodicallyinHelloTimefromthespecifiedport.MessageAgeandMaxAgeTheconfigurationinformationsavedbyporthasalifetimeMessageAgefield.Itincreasesaccordingtothetime.Whenitreceivesaconfigurationinformationwithasmallerlifetime,itwillupdateitsconfigurationinformation.Whenitdoesn’treceiveanyconfigureinformationandthelifetimeisup,thenthebridgeconsidersthatthelinkconnectingwiththisportfails,andcarriesoutthefailuretreatment.LocalAreaNetworkLinkfailuretreatmentILocalAreaNetwork23，18，123ThelifetimeofconfigurationinformationofPort4isovertime,thenthisconfigurationinformationisabandoned,andSpanningPort1Port2Port3Port4Port5blocking23，14，32123，15，8023，15，81rootB8132，0，3223，15，8123，15，81LinkfailuretreatmentIILocalAreaNetworkThelifetimeofconfigurationinformationofPort3isalsoovertime,thenthisconfigurationinformationisabandoned,andSpanningTreeisre-calculated.Port1Port2Port3Port4Port523，15，8023，16，81root23，16，8132，0，3232，18，12323，16，8123，16，81B81LinkfailuretreatmentIIILocalAreaNetworkThelifetimeofconfigurationinformationofPort5isalsoovertime,thenthisconfigurationinformationisabandoned,anditsendstheconfigurationinformation(81,0,81)forrootbridge,untilitreceivestheconfigurationinformationwithhigherpriorityfromanyport.Port1Port2Port3Port4Port581，0，8181，0，8181，0，8181，0，8181，0，81B81Redrepresentscost10,Bluerepresentscost5,BID

are42,97,45,57,83separatelyLocalAreaNetworkEvolutionSpanning-TreeProtocol(STP)Std802.1DDisadvantages:Itneedstowaitforthetimeoutofthetimer,andthenetworkrecoveryisslow.RapidSpanningTreeProtocol(RSTP,RapidSTP)Std802.1wAdvantages:Itdoesn’tneedtowaitforthetimeoutofthetimer,andincrea