Configuring Path Cost - Cisco Catalyst 3750 Software Configuration Manual

Configuring MSTP Features

Configuring Path Cost

The MSTP path cost default value is derived from the media speed of an interface. If a loop occurs, the
MSTP 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, the MSTP 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 MSTP cost of an interface. This
procedure is optional.
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 spanning-tree mst instance-id cost cost
Step 4
end
Step 5 show spanning-tree mst interface interface-id
or
show spanning-tree mst instance-id
Step 6
copy running-config startup-config
The show spanning-tree mst interface interface-id privileged EXEC command displays information
Note
only for interfaces that are in a link-up operative state. Otherwise, you can use the show running-config
privileged EXEC command to confirm the configuration.
To return the interface to its default setting, use the no spanning-tree mst instance-id cost interface
configuration command.
Catalyst 3750 Metro Switch Software Configuration Guide
15-18
Purpose
Enter global configuration mode.
Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical ports and
port-channel logical interfaces. The port-channel range is 1 to 12.
Configure the cost.
If a loop occurs, the MSTP uses the path cost when selecting an
interface to place into the forwarding state. A lower path cost
represents higher-speed transmission.
For instance-id, you can specify a single instance, a range of
•
instances separated by a hyphen, or a series of instances
separated by a comma. The range is 0 to 15.
• For cost, the range is 1 to 200000000; the default value is
derived from the media speed of the interface.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 15 Configuring MSTP
78-15870-01