Specifications

Enabling the Spanning Tree Protocol
13-2 Configuring and Managing Spanning Tree Protocol
Enabling the Spanning Tree Protocol
STPisdisabledbydefault.YoucanenableSTPgloballyoronindividualVLANs.
ToenableSTP,usethefollowingcommand:
set spantree {enable | disable} [{all | vlan vlan-id | port port-list vlan-id}]
Example
ToenableSTPonallVLANsconfiguredonaRoamAboutSwitchRoamAboutSwitch,typethe
followingcommand:
RBT-8100# set spantree enable
success: change accepted.
ToverifytheSTPstateanddisplaytheSTPparametersettings,entertheshowspantree
command.Forinformation,see“Displaying SpanningTreeInformation”onpage 13‐11.
Changing Standard Spanning Tree Parameters
YoucanchangethefollowingstandardSTP parameters:
•Bridgepriority
•Portcost
•Portpriority
Bridge Priority
ThebridgeprioritydeterminestheRoamAboutswitch’seligibilitytobecometherootbridge.You
cansetthisparametergloballyoronindividualVLANs.
Therootbridgeiselectedbasedonthebridgepriorityofeachdeviceinthespanningtree.The
devicewiththehighestbridgepriorityiselectedtobe
therootbridgeforthespanningtree.The
bridgepriorityisanumericvaluefrom0through65,535.Lowernumericvaluesrepresenthigher
priorities.Thehighestpriorityis0,andthelowestpriorityis65,535.Thedefaultbridgepriorityfor
alldevicesis32,768.
Ifmorethanonedevicehasthe
highestbridgepriority(lowestnumericvalue),thedevicewiththe
lowestMACaddressbecomestherootbridge.
Iftherootbridgefails,STPelectsanewrootbridgebasedonthebridgeprioritiesoftheremaining
bridges.
Port Cost
Portcostisanum ericvaluethatSTPaddstothetotalcostofapathtotherootbridge.Whena
designatedbridgehasmultipleequal‐costpathstotherootbridge,thedesignatedbridgeusesthe 
pathwiththelowesttotalcost.Youcansetthisparameteronan
individualportbasis,forall
VLANstheportisin,orforspecificVLANs.
Youcanspecifyavaluefrom1through65,535fortheportcost.Thedefaultdependsontheport
speedandlinktype.Table 13‐1onpage 13‐3liststhedefaultsforSTPportpathcost.