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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 15 Configuring MSTP
Configuring MSTP Features
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.
Beginning in privileged EXEC mode, follow these steps to configure a switch as the secondary root
switch. This procedure is optional.
To return the switch to its default setting, use the no spanning-tree mst instance-id root global
configuration command.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
spanning-tree mst instance-id root
secondary [diameter net-diameter
[hello-time seconds]]
Configure a switch as the secondary 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 15.
• (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.
Use the same network diameter and hello-time values that you used
when configuring the primary root switch. See the “Configuring the
Root Switch” section on page 15-14.
Step 3
end Return to privileged EXEC mode.
Step 4
show spanning-tree mst instance-id Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.