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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter14 Configuring STP Configuring Spanning-Tree Features
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.
Beginning in privileged EXEC mode, follow these steps to configure the cost of an interface. This
procedure is optional.
Note The show spanning-tree interface interface-id privileged EXEC command displays information only
for ports that are in a link-up operative state. Otherwise, y ou can use the show running-conf ig pri vile ged
EXEC command to confirm the configuration.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical interfaces
and port-channel logical interfaces (port-channel
port-channel-number).
Step3 spanning-tree cost cost Configure the cost for an interface.
If a loop occurs, spanning tree uses the path cost when selecting
an interface to place into the forwarding state. A lower path cost
represents higher-speed transmission.
For cost, the range is 1 to 200000000; the default value is derived
from the media speed of the interface.
Step4 spanning-tree vlan vlan-id cost cost Configure the cost for a VLAN.
If a loop occurs, spanning tree uses the path cost when selecting
an interface to place into the forwarding state. A lower path cost
represents higher-speed transmission.
•For vlan-id, you can specify a single VLAN identified by
VLAN ID number, a range of VLANs separated by a hyphen,
or a series of VLANs separated by a comma. The range is 1
to 1005 when the SI is installed and 1 to 4094 when the EI is
installed.
•For cost, the range is 1 to 200000000; the default value is
derived from the media speed of the interface.
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.