Configuring A Secondary Root Switch - Cisco Catalyst 3750-X Software Configuration Manual

Chapter 20 Configuring STP
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the
specified VLAN. This procedure is optional.
Command
Step 1
configure terminal
Step 2
spanning-tree vlan vlan-id root primary
[diameter net-diameter [hello-time seconds]]
Step 3
end
Step 4 show spanning-tree detail
Step 5
copy running-config startup-config
To return to the default setting, use the no spanning-tree vlan vlan-id root global configuration
command.

Configuring a Secondary Root Switch

When you configure a switch 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 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.
OL-21521-01
Purpose
Enter global configuration mode.
Configure a switch to become the root for the specified VLAN.
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.
(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; the default is 2.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Configuring Spanning-Tree Features
20-17