Configuring A Secondary Root Bridge - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Chapter 17 Configuring STP and MST
Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number of
bridge hops between any two end stations in the Layer 2 network). When you specify the network
diameter, the Catalyst 6500 series switch automatically selects an optimal hello time, forward delay
time, and maximum age time for a network of that diameter, which can significantly reduce the STP
convergence time. You can use the hello keyword to override the automatically calculated hello time.
To preserve a stable STP topology, we recommend that you avoid configuring the hello time, forward
Note
delay time, and maximum age time manually after configuring the Catalyst 6500 series switch as the root
bridge.
To configure a Catalyst 6500 series switch as the root bridge, perform this task:
Command
Step 1
Router(config)# spanning-tree vlan vlan_ID root
primary [diameter hops [hello-time seconds]]
Router(config)# no spanning-tree vlan vlan_ID
root
Step 2
Router(config)# end
This example shows how to configure the Catalyst 6500 series switch as the root bridge for VLAN 10,
with a network diameter of 4:
Router# configure terminal
Router(config)# spanning-tree vlan 10 root primary diameter 4
Router(config)# end
Router#

Configuring a Secondary Root Bridge

When you configure a Catalyst 6500 series switch as the secondary root, the STP bridge priority is
modified from the default value (32768) so that the switch is likely to become the root bridge for the
specified VLANs if the primary root bridge fails (assuming the other network devices in the network use
the default bridge priority of 32768).
With the extended system ID is enabled, STP sets the bridge priority to 28672.
You can run this command on more than one switch to configure multiple backup root bridges. Use the
same network diameter and hello time values as you used when configuring the primary root bridge.
OL-11439-03
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Purpose
Configures a Catalyst 6500 series switch as the root
bridge. The vlan_ID value can be 1 through 4094, except
reserved VLANs (see Table 17-6 on page
Clears the root bridge configuration.
Exits configuration mode.
Configuring STP
17-26).
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