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Chapter 19
Configuring MSTP
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.
Command
Step 1
configure terminal
Step 2
spanning-tree mst instance-id root
secondary [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 Port Priority
If a loop occurs, the MSTP uses the port priority when selecting an interface to put into the forwarding
state. You can assign higher priority values (lower numerical values) to interfaces that you want selected
first and lower priority values (higher numerical values) that you want selected last. If all interfaces have
the same priority value, the MSTP puts the interface with the lowest interface number in the forwarding
state and blocks the other interfaces.
OL-12247-04
Purpose
Enter global configuration mode.
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 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.
Use the same network diameter and hello-time values that you used
when configuring the primary root switch. See the
Root Switch" section on page
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
Configuring MSTP Features
"Configuring the
19-17.
19-19
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