Setting the bridge priority for an instance


spanning-tree instance 1..16 priority priority-multiplier

Sets the switch (bridge) priority for the designated instance. This priority is compared with the priorities of other switches in the same instance to determine the root switch. The lower the priority value, the higher the priority. If there is only one switch in the instance, then that switch is the root switch for the instance. The IST regional root bridge provides the path to instances in other regions that share one or more of the same VLANs.

The priority range for an MSTP switch is 0 - 61440. However, this command specifies the priority as a multiplier (0 - 15) of 4096. When a priority multiplier value is set from 0 - 15, the actual priority assigned to the switch for the specified MST instance is: (priority-multiplier) x 4096

For example, if you configure 5 as the priority-multiplier for MST Instance 1 on a given MSTP switch, the Switch Priority setting is 20,480 for that instance in that switch.


If multiple switches in the same MST instance have the same priority setting, the switch with the lowest MAC address becomes the root switch for that instance.