Specifications

Understanding and Configuring Loop Protect
March 14, 2011 Page 26 of 29
TheLoopProtectwindowisatimervalue,inseconds,thatdefinesaperiodduringwhichLoop
Protecteventsarecounted.Thedefaultvalueis180seconds.Ifthetimerissetto0,theevent
counterisnotresetuntiltheLoopProtecteventthresholdisreached.
Usethiscommand
tosettheLoopProtecteventwindowvalueinseconds:
set spantree lpwindow value
Enabling or Disabling Loop Protect Event Notifications
LoopProtecttrapsaresentwhenaLoopProtecteventoccurs,thatis,whenaportgoestolistening
duetonotreceivingBPDUs.Thetrapindicatesport,SIDandloopprotectionstatus.
UsethiscommandtoenableordisableLoopProtecteventnotification.Bydefault,thisisdisabled:
set spantree lptrapenable {enable | disable}
Setting the Disputed BPDU Threshold
AdisputedBPDUisoneinwhichtheflagsfieldindicatesadesignatedroleandalearningstate,
andthepriorityvectorisworsethanthatalreadyheldbytheport.IfadisputedBPDUisreceived,
theportisforcedtothelisteningstate.Refertothe802.1Q‐2005standard,
IEEEStandardforLocal
andMetropolitanAreaNetworks–VirtualBridgedLocalAreaNetworks,forafulldesc riptionofthe 
disputemechanism,whichpreventsloopingincasesofone‐waycommunication.
ThedisputedBPDUthresholdisanintegervariablethatrepresentsthenumberofdisputed
BPDUsthatmustbereceived
onagivenport/SIDuntiladisputedBPDUtrapissentandasyslog
messageisissued.Forexample,ifthethresholdis10,thenatrapisissuedwhen10,20,30(andso
on)disputedBPDUshavebeenreceived.Thetrapindicatesport,SIDandtotalDisputedBPDU
count.
UsethiscommandtosetthedisputedBPDUthreshold:
set spantree disputedbpduthreshold value
Defaultvalueis0,whichmeansthattrapsarenotsent.
Monitoring Loop Protect Status and Settings
UsethecommandsinTable 8tomonitorLoopProtectsettings.
Table 8 Commands for Monitoring Loop Protect
Task Command
Display the Loop Protect status per port, per SID, or
both.
show spantree lp [port port-string]
[sid sid
]
Display the Loop Protect lock status per port, per
SID, or both.
Note: A port can become locked if a configured
number of Loop Protect events occur during
the configured window of time. Once a port is
forced into blocking (locked), it remains locked
until manually unlocked with the
clear spantree
lplock command.
show spantree lplock [port port-string]
[sid sid]
Display the Loop Protect capability of a link
partner for one or more ports.
show spantree lpcapablepartner [port
port-string]