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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring STP
Configuring Spanning-Tree Features
Configuring 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 forwarding state. You can assign
lower cost values to interfaces that you want selected first and higher cost values that you want selected
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 interfaces.
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, you can use the show running-config privileged
EXEC command to confirm the configuration.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical ports and
port-channel logical interfaces (port-channel
port-channel-number).
Step 3
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.
Step 4
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 4094.
• For cost, the range is 1 to 200000000; the default value is
derived from the media speed of the interface.
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.
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