Configuring A Secondary Root Switch - Cisco Catalyst 2928 Software Configuration Manual

Configuring MSTP Features
Beginning in privileged EXEC mode, follow these steps to configure a switch as the root switch. This
procedure is optional.
Command
Step 1 configure terminal
Step 2
spanning-tree mst instance-id root primary
[diameter net-diameter [hello-time seconds]]
Step 3
end
Step 4
show spanning-tree mst instance-id
Step 5 copy running-config startup-config
To return the switch to its default setting, use the no spanning-tree mst instance-id root 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-id root primary global configuration command.
Catalyst 2928 Switch Software Configuration Guide
17-18
Purpose
Enter global configuration mode.
Configure a switch as the root switch.
• For instance-id, you can specify a single instance, a range
of 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-time seconds, 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.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 17 Configuring MSTP
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