Specifications

Functions and Features Supported on Enterasys Devices
March 14, 2011 Page 5 of 29
•FurtherprotectingyournetworkfromloopformationwithLoopProtect,asdescribedbelow
andin“UnderstandingandConfiguringLoopProtect”onpage22.
• Supportingmoreportdensityandfasterportspeedsasdescribedin“Updated802.1t”on
page 5.
SpanGuard
TheEnterasysSpanGuardfeaturehelpsprotectyournetworkfromtwosituationsthatcancausea
DenialofServicecondition:repeatedtopologychangenotificationsandanunwantedbridgebeing
insertedintoandforcingtrafficthroughthetopology.
SpanGuardincreasessecurityandreliabilitybypreventingSpanningTreerespansthatcanoccur
whenBPDUs
arereceivedonedge(user)ports,andnotifiesnetworkmanagementthattheywere
attempted.
IfaSpanGuardenabledportreceivesaBPDU,itbecomeslockedandtransitionstotheblocking
state.Itwillonlytransitionoutoftheblockingstateafteragloballyspecifiedtimeorwhenitis
manuallyunlocked.
Bydefault,SpanGuardisgloballydisabledonN‐Series,S‐Series,stackable,and standaloneswitch
devicesandmustbegloballyenabledtooperateonalluserports.Forconfigurationinformation,
referto“UnderstandingandConfiguringSpanGuard”onpage 20.
Loop Protect
TheLoopProtectfeaturepreventsorshortcircuitsloopformationcausedbyredundantpathsin
yournetworkbyrequiringportstoreceivetype2BPDUs(RSTP/MSTP)onpoint‐to‐pointinter‐
switchlinks(ISLs)beforetheirstates areallowedtobecomeforwarding.Further,ifaBPDU
timeoutoccursonaport,
itsstatebecomeslisteninguntilaBPDUisreceived.
Inthisway,bothupstreamanddownstreamfacingportsareprotected.Whenarootoralternate
portlosesitspathtotherootbridgeduetoamessageageexpiration,ittakesontheroleof
designatedportandwillnot
forwardtrafficuntilaBPDUisreceived.Whenaportisintendedto
bethedesignatedportinanISL,itconstantlyproposesandwillnotforwarduntilaBPDUis
received,andwillreverttolisteningifitfailstogetaresponse.Thisprotectsagainst
misconfigurationandprotocolfailure
bytheconnectedbridge.
Bydefault,theLoopProtectfeatureisgloballydisabledonEnterasysswitchdevicesandmustbe
globallyenabledtooperateonallports.Forconfigurationinformation,referto“Understanding
andConfiguringLoopProtect”onpage 22.
Updated 802.1t
IEEE802.1tisenabledbydefaultonEnterasysswitchdevices.ThisupdatedSpanningTree
protocolsupportsmultipleSpanningTrees,moreswitchportdensityandfasterportspeeds.
802.1tincludesthefollowingupdates:
•Newbridgeidentifierencoding(4‐bitpriority,12‐bitsystemIDextension,48‐bitbridge
address)
•Newportidentifierencoding(4
‐bitpriority,12‐bitportnumber)
•Bridgedetectionstatemachine(foredgeportidentifica tion)
• Pathcostdefaultvalues(switchbetweenoldandnewdefaultvalues)