Cisco Systems 3750E manual 19-19

Chapter 19 Configuring MSTP

Configuring MSTP Features

	Command	Purpose
Step 4
	show spanning-tree mst instance-id	Verify your entries.
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the switch to its default setting, use the no spanning-tree mst instance-idroot global configuration command.

Configuring a Secondary Root Switch

When you configure a switch with the extended system ID support as the secondary root, the switch priority is modified from the default value (32768) to 28672. The switch is then likely to become the root switch for the specified instance if the primary root switch fails. This is assuming that the other network switches use the default switch priority of 32768 and therefore are unlikely to become the root switch.

You can execute this command on more than one switch to configure multiple backup root switches. Use the same network diameter and hello-time values that you used when you configured the primary root switch with the spanning-tree mst instance-idroot primary global configuration command.

Beginning in privileged EXEC mode, follow these steps to configure a switch as the secondary root switch. This procedure is optional.

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	spanning-tree mst instance-idroot	Configure a switch as the secondary root switch.
	secondary [diameter net-diameter	• For instance-id, you can specify a single instance, a range of
	[hello-time seconds]]
		instances separated by a hyphen, or a series of instances
		separated by a comma. The range is 0 to 4094.
		• (Optional) For diameter net-diameter, specify the maximum
		number of switches between any two end stations. The range is 2
		to 7. This keyword is available only for MST instance 0.
		• (Optional) For hello-timeseconds, specify the interval in
		seconds between the generation of configuration messages by
		the root switch. The range is 1 to 10 seconds; the default
		is 2 seconds.
		Use the same network diameter and hello-time values that you used
		when configuring the primary root switch. See the “Configuring the
		Root Switch” section on page 19-17.
Step 3
	end	Return to privileged EXEC mode.
Step 4
	show spanning-tree mst instance-id	Verify your entries.
Step 5
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To return the switch to its default setting, use the no spanning-tree mst instance-idroot global configuration command.

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