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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 11 Configuring STP
Configur ing Spanning-Tree F eatures
Note Th e show spanning-tree interface interface-id privileged EXEC command displa ys informa tion only
if th e por t is i n a l ink -up op er ative state . O the rwi se, y ou can use th e show running-config interface
privileged EX EC c omm and to con firm th e co nfigurat ion.
To return the interface to its default setting, use the no spanning-tree [vlan vlan-id] port-priority
interfac e co nfigurat ion c omm and. For i nfo rmat ion o n h ow to co nfigure l oad sh ar ing on trun k p ort s by
using spanning-tree port priorities, see the “Load Sh ar ing Usin g STP ” section on page 14-21.

Configuring the Path Cost

The spanni ng-tr ee path c ost defaul t value i s derived from the med ia speed of an interfac e. If a loop
occurs , spanning tree uses c ost when s electing an interfa ce to put in the f orwar ding sta te. You can assign
lo we r c ost values to inter f a ces that you want selec ted first and higher cost values that you w an t sele cte d
last. If all interfaces have the same cost value, spanning tree puts the interface with the lowest interface
number in t he for war ding sta te a nd blo cks the o the r in terfa ces.
Spannin g tree uses the cost v alu e when the interf ace is con figu red as an access port and uses VLAN po rt
cost values when the interface is configured as a trunk port.
Beginning in privileged EXEC mode, follow these steps to configure the cost of an interface:
Step 3 spanning-tree port-priority priority Conf igure the port priority for an interface th at is an access
port.
For priority, the ra nge is 0 to 25 5; t he de fault is 128. T he
lower the number, the higher the priority.
Step 4 spanning-tree vlan vlan-id port-priority priority Configur e th e VLAN p ort p ri ority for an int er fac e th at is a
trunk p ort.
•For vlan-id, the range is 1 to 4094 whe n the EI is
installed an d 1 to 1005 when the SI is installed. Do not
enter l e ad in g zero s .
•For priority, the ra nge i s 0 to 25 5; t he de fault is 128.
The lower the number, the higher the priority.
Step 5 end Return to privileged EXEC mode.
Step 6 show spanning-tree interface interface-id
or
show spanning-tree vlan vlan-id
Verify your entries.
Step 7 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step 1 configure terminal Enter glob al co nfigur atio n mo de .
Step 2 interface interface-id Enter interface configuration mode, and specify an interface to
configure. Valid interfaces include physical interfaces and
port-channel logical interfaces (port-channel
port-channel-number).