14-17
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 14 Configuring MSTP
Configuring MSTP Features
Configuring the Port Priority
If a loop occurs, the MSTP uses the port priority when selecting an interface to put into the forwarding
state. You can assign higher priority values (lower numerical values) to interfaces that you want selected
first and lower priority values (higher numerical values) that you want selected last. If all interfaces have
the same priority 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 port priority of an
interface. This procedure is optional.
Note The show spanning-tree mst interface interface-id privileged EXEC command displays information
only if the port is in a link-up operative state. Otherwise, you can use the show running-config interface
privileged EXEC command to confirm the configuration.
To return the interface to its default setting, use the no spanning-tree mst instance-id port-priority
interface configuration command.
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 channels.
Valid port-channel numbers are 1 to 6.
Step 3
spanning-tree mst instance-id port-priority priority Configure the port priority for an MST instance.
• 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 priority, the range is 0 to 240 in increments of 16.
The default is 128. The lower the number, the higher
the priority.
Valid priority values are 0, 16, 32, 48, 64, 80, 96, 112,
128, 144, 160, 176, 192, 208, 224, and 240. All other
values are rejected.
Step 4
end Return to privileged EXEC mode.
Step 5
show spanning-tree mst interface interface-id
or
show spanning-tree mst instance-id
Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
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