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Catalyst2950 Desktop Switch Software Configuration Guide
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Chapter10 Configuring STP
Configuring Spanning-Tree Features
Note The show spanning-tree interface interface-id privileged EXEC command displays information only
if the port is in a link-up operative state. Otherwise, y ou can use th e show running-config interface
privileged EXEC command to confirm the configuration.
To return the interface to its default setting, use the no spanning-tree [vlan vlan-id] port-priority
interface configuration command. For information on how to configure l oad sh ar ing on trun k p ort s by
using spanning-tree port priorities, see the “Load Sharing Using STP” section on page13-21.
Configuring the Path Cost
The spanning-tree path cost default value is derived from the media speed of an interface. If a loop
occurs, spanning tree uses cost when selecting an interface to put in the forwar ding sta te. You can assign
lower cost values to interfaces that you want selected first and higher cost values that you w ant sele cted
last. If all interfaces have the same cost value, spanning tree puts the interface with the lowest interface
number in the forwarding state and blocks the other interfa ces.
Spanning tree uses the cost value when the interface is configured as an access port and uses VLA N port
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:
Step3 spanning-tree port-priority priority Configure the port priority for an interface that is an access
port.
For priority, the range is 0 to 255; the default is 128. The
lower the number, the higher the priority.
Step4 spanning-tree vlan vlan-id port-priority priority Configure the VLAN port priority for an interface that is a
trunk port.
•For vlan-id, the range is 1 to 4094 when the EI is
installed and 1 to 1005 when the SI is installed. Do not
enter leading zeros.
•For priority, the range is 0 to 255; the default is 128.
The lower the number, the higher the priority.
Step5 end Return to privileged EXEC mode.
Step6 show spanning-tree interface interface-id
or
show spanning-tree vlan vlan-id
Verify your entries.
Step7 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 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).