Multiple Instance Spanning-Tree Operation

802.1s Multiple Spanning Tree Protocol (MSTP)

Syntax: spanning-tree instance < 1..16 > [e] < port-list> priority <priority-multiplier>

This command sets the priority for the specified port(s) in the specified MST instance. (For a given port, the priority setting can be different for different MST instances to which the port may belong.) The priority range for a port in a given MST instance is 0-255. However, this command specifies the priority as a multiplier (0 - 15) of 16. That is, when you specify a priority multiplier of 0 - 15, the actual priority assigned to the switch is:

(priority-multiplier)x 16

For example, if you configure “2” as the priority multiplier on a given port in an MST instance, then the actual Priority setting is 32. Thus, after you specify the port priority multiplier in an instance, the switch displays the actual port priority (and not the multiplier) in the show spanning-tree instance < 1..16 > or show spanning-tree < port-list> instance < 1..16 > displays.

You can view the actual multiplier setting for ports in the specified instance by executing show running and looking for an entry in this format:

spanning-tree instance < 1..15 > < port-list> priority < priority- multiplier >

For example, configuring port A2 with a priority multiplier of “3” in instance 1, results in this line in the show running output:

spanning-tree instance 1 A2 priority 3

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