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1、CHAPTER35ConfiguringFallbackBridgingThischapterdescribeshowtoconfigurefallbackbridging(VLANbridging)onyourCatalyst3550switch.Withfallbackbridging,youcanforwardnon-IPpacketsthattheswitchdoesnotroutebetweenVLANbridgedomainsandroutedports.Tousethisfeature,youmustha
2、vetheenhancedmultilayersoftware(EMI)imageinstalledonyourswitch.NoteForcompletesyntaxandusageinformationforthecommandsusedinthischapter,refertotheCiscoIOSBridgingandIBMNetworkingCommandReferenceforRelease12.1.Thischapterconsistsofthesesections:•UnderstandingFallb
3、ackBridging,page35-1•ConfiguringFallbackBridging,page35-3•MonitoringandMaintainingFallbackBridging,page35-12UnderstandingFallbackBridgingWithfallbackbridging,theswitchbridgestogethertwoormoreVLANsorroutedports,essentiallyconnectingmultipleVLANswithinonebridgedom
4、ain.FallbackbridgingforwardstrafficthattheswitchdoesnotrouteandforwardstrafficbelongingtoanonroutableprotocolsuchasDECnet.FallbackbridgingdoesnotallowthespanningtreesfromtheVLANsbeingbridgedtocollapse;eachVLANhasitsownspanning-treeinstanceandaseparatespanningtre
5、e,calledtheVLAN-bridgespanningtree,whichrunsontopofthebridgegrouptopreventloops.AVLANbridgedomainisrepresentedwithswitchvirtualinterface(SVI).AsetofSVIsandroutedports(whichdonothaveanyVLANsassociatedwiththem)canbeconfigured(groupedtogether)toformabridgegroup.Rec
6、allthatanSVIrepresentsaVLANofswitchportsasoneinterfacetotheroutingorbridgingfunctioninthesystem.YouassociateonlyoneSVIwithaVLAN,andyouconfigureanSVIforaVLANonlywhenyouwanttoroutebetweenVLANs,tofallback-bridgenonroutableprotocolsbetweenVLANs,ortoprovideIPhostconn
7、ectivitytotheswitch.Aroutedportisaphysicalportthatactslikeaportonarouter,butitisnotconnectedtoarouter.AroutedportisnotassociatedwithaparticularVLAN,doesnotsupportVLANsubinterfaces,butbehaveslikeanormalroutedinterface.FormoreinformationaboutSVIsandroutedports,see
8、Chapter10,“ConfiguringInterfaceCharacteristics.”Abridgegroupisaninternalorganizationofnetworkinterfacesonaswitch.Bridgegroupscannotbeusedtoidentifytrafficswitchedwith
