Cisco ME 3400 Command Reference Manual page 675

Chapter 2 Cisco ME 3400 Ethernet Access Switch Cisco IOS Commands
When you enter the spanning-tree mst instance-id root command, the software tries to set a high
enough priority to make this switch the root of the spanning-tree instance. Because of the extended
system ID support, the switch sets the switch priority for the instance to 24576 if this value will cause
this switch to become the root for the specified instance. If any root switch for the specified instance has
a switch priority lower than 24576, the switch sets its own priority to 4096 less than the lowest switch
priority. (4096 is the value of the least-significant bit of a 4-bit switch priority value.)
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).
Examples
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
command.
Related Commands Command
show spanning-tree
spanning-tree mst forward-time
spanning-tree mst hello-time
spanning-tree mst max-age
spanning-tree mst max-hops
OL-9640-10
Description
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
discarded.
Cisco ME 3400 Ethernet Access Switch Command Reference
spanning-tree mst root
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