Cisco Catalyst 2960 Series, Configuration Manual

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Configuring a Secondary Root Device
When you configure a switch as the secondary root, the switch priority is modified from the default value
(32768) to 28672. With this priority, the switch is likely to become the root switch for the specified VLAN
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 vlan vlan-id root primary global configuration command.
This procedure is optional.
SUMMARY STEPS
1. enable
2.
configure terminal
3. spanning-tree vlan vlan-id root secondary [ diameter net-diameter
4.
end
DETAILED STEPS
Purpose Command or Action
Enables privileged EXEC mode. Enter your password if prompted. enable Step 1
Example:
Switch> enable
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 2
Configures a switch to become the secondary root for the specified
VLAN. spanning-tree vlan vlan-id root secondary
[ diameter net-diameter
Step 3
Example:
Switch(config)# spanning-tree vlan
20-24 root secondary diameter 4
• For vlan-id , you can specify a single VLAN identified by VLAN
ID number, a range of VLANs separated by a hyphen, or a series
of VLANs separated by a comma. The range is 1 to 4094.
• (Optional) For diameter net-diameter , specify the maximum
number of switches between any two end stations. The range is 2
to 7.
Use the same network diameter value that you used when configuring
the primary root switch.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
229
How to Configure Spanning-Tree Features