Cisco Systems 3750E manual Spanning-tree mst instance-id port-priority priority, 19-20

Chapter 19 Configuring MSTP

Configuring MSTP Features

Configuring 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.

Note If your Catalyst 3750-E switch is a member of a switch stack, you must use the spanning-tree mst [instance-id] cost cost interface configuration command instead of the spanning-tree mst [instance-id] port-prioritypriority interface configuration command to select a port to put in the forwarding state. Assign lower cost values to ports that you want selected first and higher cost values to ports that you want selected last. For more information, see the “Configuring Path Cost” section on page 19-21.

Beginning in privileged EXEC mode, follow these steps to configure the MSTP port priority of an interface. This procedure is optional.

	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. The port-channel range is 1 to 48.
Step 3
	spanning-tree mst instance-idport-priority priority	Configure the port priority.
		• 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
		4094.
		• For priority, the range is 0 to 240 in increments of 16.
		The default is 128. The lower the number, the higher
		the priority.
		The 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	Verify your entries.
	or
	show spanning-tree mst instance-id
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

Note The show spanning-tree mst interface interface-idprivileged 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.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
19-20	OL-9775-02