Specifications

Configuring STP and RSTP
March 14, 2011 Page 14 of 29
Setting a Port Priority
YoucansetaSpanningTreeportpriority,avaluetobeusedtobreakatiewhenchoosingtheroot
portforabridgeinacasewherethechoiceisbetweenportsconnectedtothesa mebridge.The
portwiththelowestvaluewillbeelected.
Usethiscommand
tosetaportpriority:
set spantree portpri port-string priority [sid sid]
Validpriorityvaluesare0–240(inincrementsof16)with0indicatinghighpriority.
Validsidvaluesare0
–4094.Ifnotspecified,SID0willbeassumed.
Assigning Port Costs
EachinterfacehasaSpanningTreeportcostassociatedwithit,whichhelpstodeterminethe
quickestpathbetweentherootbridgeandaspecifieddestination.Byconvention,thehigherthe
portspeed,thelowertheportcost.Bydefault,thisvalueissetto0,whichforcestheportto

recalculateSpanningTreeportcostbasedonthespeedoftheportandwhetherornotlegacy
(802.1D)pathcostisenabled.
UsethiscommandtoassigndifferentSpanningTreeportcosts:
set spantree adminpathcost port-string cost [sid sid]
Va1idcostvaluesare:
– 0
–65535iflegacypathcostisenabled.
– 0
–200000000iflegacypathcostisdisabled.
Validsidvaluesare0
–4094.Ifnotspecified,SID0willbeassumed.
Adjusting Bridge Protocol Data Unit (BPDU) Intervals
UsethecommandsinthissectiontoadjustdefaultBPDUintervalvalues.
Notes: Please refer to the IEEE 802.1D specification for guidance in setting appropriate cost
values for your port speeds.
By default, legacy path cost is disabled. Enabling the device to calculate legacy path costs affects
the range of valid values that can be administratively assigned.
To check the status of legacy path cost, use show spantree legacypathcost.
To disable legacy path cost, if necessary use set spantree legacypathcost disable.
Table 5 BPDU Interval Defaults
BPDU Interval Default Value
Hello time (bridge and ports) 2 seconds
Forward delay 15 seconds
Maximum age time 20 seconds