Enterasys b5

Configuring Spanning Tree Bridge Parameters
Enterasys B5 CLI Reference 9-3
listeningifitfailstogetaresponse.Thisprotectsagainstmisconfigurationandprotocolfailureby
theconnectedbridge.
TheDisputedBPDUmechanismprotectsagainstloopinginsituationswherethereisoneway
communication.AdisputedBPDUisoneinwhichtheflagsfieldindicatesadesignatedroleand
learningand
thepriorityvectorisworsethan tha talreadyheldbytheport.IfadisputedBPDUis
received,theportisforcedtothelisteningstate.WhenaninferiordesignatedBPDUwiththe
learningbitsetisreceivedonadesignatedport,itsstateissettodiscardingtopreventloop

formation.NotethattheDisputemechanismisalwaysactive regardlessoftheconfiguration
settingofLoopProtection.
LoopProtectoperatesasaperport,perMSTinstancefeature.Itshouldbesetoninter‐switch
links.Itiscomprisedofseveralrelatedfunctions:
• Controlofportforwardingstatebasedonreception
ofagreementBPDUs
• ControlofportforwardingstatebasedonreceptionofdisputedBPDUs
• Communicatingportnon‐forwardingstatusthroughtrapsandsyslogmessages
•Disablingaportbasedonfrequencyoffailureevents
PortforwardingstateinthedesignatedportisgatedbyatimerthatissetuponBPDUreception.It
is
analogoustothercvdInfoWhiletimertheportuseswhenreceivingrootinformationintheroot/
alternate/backuprole.
TherearetwooperationalmodesforLoopProtectonaport.Iftheportisconnectedtoadevice
knowntoimplementLoopProtect,itusesfullfunctionalmode.Otherwisetheportoperatesin

limitedfunctionalmode.
ConnectiontoaLoopProtectswitchguaranteesthatthealternateagreementmechanismis
implemented.Thismeansthedesignatedportcanrelyonreceivingaresponsetoitsproposal
regardlessoftheroleoftheconnectedport,whichhastwoimportantimplications.First,the
designatedportconnectedto
anon‐rootportmaytransitiontoforwarding.Second,thereisno
ambiguitywhenatimeouthappens;aLoopProtecteventhasoccurred.
Infullfunctionalmode,whenatype2BPDUisreceivedandtheportisdesignatedandpoint‐to‐
point,thetimerissetto3timeshelloTime.
Inlimitedfunctionalmodethereistheadditional
requirementthattheflagsfieldindicatearootrole.IftheportisaboundaryporttheMSTIsfor
thatportfollowtheCIST,thatis,theMSTIporttimersaresetaccordingtotheCISTporttimer.If
theportis
internaltotheregionthentheMSTIporttimersaresetindependentlyusingthe
particularMSTImessage.
MessageageexpirationandtheexpirationoftheLoopProtecttimerarebothLoopProtectevents.
Anoticelevelsyslogmessageisproducedforeachsuchevent.Trapsmaybeconfiguredtoreport
these
eventsaswell.AsyslogmessageandtrapmaybeconfiguredfordisputedBPDUs.
Itisalsoconfigura bletoforcethelockingofaSID/portfortheoccurrenceofoneormoreevents.
Whentheconfigurednumberofeventshappenwithinagivenwindowoftime,theportisforced
into
blockingandheldthereuntilitismanuallyunlockedviamanagement.
Configuring Spanning Tree Bridge Parameters
Purpose
TodisplayandsetSpanningTreebridgeparameters,incl udingdevicepriorities,hellotime,
maximumwaittime,forwarddelay,pathcost,andtopologychangetrapsuppression.