Enterasys Networks DFE-Gold Series Spanning Tree Configuration

Enterasys Matrix DFE-Gold Series Configuration Guide 6-1
6
Spanning Tree Configuration
ThischapterdescribestheSpanningTreeConfigurationsetofcommandsandhowtousethem.
Overview: Single, Rapid and Multiple Spanning Tree Protocols
TheIEEE802.1DSpanningTreeProtocol(STP)resolvestheproblemsofphysicalloopsina
networkbyestablishingoneprimarypathbetweenanytwodevicesinanetwork.Anyduplicate
pathsarebarredfromuseandbecomestandbyorblockedpathsuntiltheoriginalpathfails,at
whichpointtheycanbebroughtintoservice.
RSTP
TheIEEE802.1wRapidSpanningProtocol(RSTP),anevolutionof802.1D,canachievemuch
fasterconvergencethanlegacySTPinaproperlyconfigurednetwork.RSTPsignificantlyreduces
thetimetoreconfigurethenetwork’sactivetopologywhenphysicaltopologyorconfiguration
parameterchangesoccur.ItselectsoneswitchastherootofaSpanningTree‐connectedactive
topologyandassignsportrolestoindividualportsontheswitch,dependingonwhetherthatport
ispartoftheactivetopology.
RSTPprovidesrapidconnectivityfollowingthefailureofaswitch,switchport,oraLAN.Anew
rootportandthedesignatedportontheothersideofthebridgetransitiontoforwardingthrough
anexplicithandshakebetweenthem.Bydefault,userportsareconfiguredtorapidlytransitionto
forwardinginRSTP.
MSTP
TheIEEE802.1sMultipleSpanningTreeProtocol(MSTP)buildsupon802.1DandRSTPby
optimizingutilizationofredundantlinksbetweenswitchesinanetwork.Whenredundantlinks
existbetweenapairofswitchesrunningsingleSTP,onelinkisforwardingwhiletheothersare
blockingforalltrafficflowingbetweenthetwoswitches.Theblockinglinksareeffectivelyused
onlyiftheforwardinglinkgoesdown.MSTPassignseachVLANpresentonthenetworktoa
particularSpanningTreeinstance,allowingeachswitchporttobeinadistinctstateforeachsuch
instance:blockingforoneSpanningTreewhileforwardingforanother.Thus,trafficassociated
withonesetofVLANscantraverseaparticularinter‐switchlink,whiletrafficassociatedwith
anothersetofVLANscanbeblockedonthatlink.IfVLANsareassignedtoSpanningTrees
wisely,nointer‐switchlinkwillbecompletelyidle,maximizingnetworkutilization.
For information about... Refer to page...
Overview: Single, Rapid and Multiple Spanning Tree Protocols 6-1
Configuring Spanning Tree Bridge Parameters 6-3
Configuring Spanning Tree Port Parameters 6-49
Configuring Spanning Tree Loop Protect Features 6-65