Configuring A Secondary Root Switch - Cisco WS-C3550-12G Software Configuration Manual

Configuring Basic STP Features
Beginning in privileged EXEC mode, follow these steps to configure a switch as the root switch:
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
Step 5
copy running-config startup-config
To return the switch to its default setting, use the no spanning-tree vlan vlan-id root global
configuration command.

Configuring a Secondary Root Switch

When you configure a Catalyst 3550 switch that supports the extended system ID as the secondary root,
the STP switch priority is modified from the default value (32768) to 28672 so that the switch is likely
to become the root switch for the specified VLAN if the primary root switch fails (if the other switches
in the network use the default switch priority of 32768, and therefore, are unlikely to become the root
switch). For Catalyst 3550 switches without the extended system ID support (software before Release
12.1(8)EA1), the switch priority is changed to 16384.
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 as you used when configuring the primary root switch.
Catalyst 3550 Multilayer Switch Software Configuration Guide
10-24
Purpose
Enter global configuration mode.
Configure a switch as the root switch.
• For vlan-id, the range is 1 to 1005. Do not enter leading
zeros.
• (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 seconds; the
default is 2 seconds.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 10 Configuring STP
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