Cisco Catalyst 3750-X Command Reference Manual page 916

Cisco ios release 15.2(1)e and later

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spanning-tree mst root

When you enter the spanning-tree mst instance-id root secondary command, because of support for

the extended system ID, the software changes the switch priority from the default value (32768) to

28672. If the root switch fails, this switch becomes the next root switch (if the other switches in the

network use the default switch priority of 32768 and are therefore unlikely to become the root switch).

This example shows how to configure the switch as the root switch for instance 10 with a network

diameter of 4:

Switch(config)# spanning-tree mst 10 root primary diameter 4

This example shows how to configure the switch as the secondary root switch for instance 10 with a

network diameter of 4:

Switch(config)# spanning-tree mst 10 root secondary diameter 4

You can verify your settings by entering the show spanning-tree mst instance-id privileged EXEC

Related Commands

show spanning-tree

spanning-tree mst forward-time

spanning-tree mst hello-time

spanning-tree mst max-age

spanning-tree mst max-hops

Catalyst 3750-X and 3560-X Switch Command Reference

Chapter 2 Catalyst 3750-X and 3560-X Switch Cisco IOS Commands

mst instance-id

Displays MST information for the specified instance.

Sets the forward-delay time for all MST instances.

Sets the interval between hello BPDUs sent by root switch

configuration messages.

Sets the interval between messages that the spanning tree

receives from the root switch.

Sets the number of hops in a region before the BPDU is

Catalyst 3560-x