Cisco 7609 User Manual

15-26
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
78-14064-04
Chapter 15 Configuring STP and IEEE 802.1s MST
Configuring STP
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 Cisco 7600 series router 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.
Note To preserve a stable STP topology, we recommend that you avoid configuring the hello time, forward
delay time, and maximum age time manually after configuring the Cisco 7600 series router as the root
bridge.
To configure a Cisco 7600 series router as the root bridge, perform this task:
This example shows how to configure the Cisco 7600 series router 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 Cisco 7600 series router as the secondary root, the STP bridge priority is modified
from the default value (32768) so that the router 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).
If the extended system ID is enabled, STP sets the bridge priority to 28672. If the extended system ID is
disabled, STP sets the bridge priority to 16384.
You can run this command on more than one Cisco 7600 series router to configure multiple backup root
bridges. Use the same network diameter and hello time values as you used when configuring the primary
root bridge.
Command Purpose
Step 1
Router(config)# spanning-tree vlan vlan_ID root
primary [diameter hops [hello-time seconds]]
Configures a Cisco 7600 series router as the root bridge.
The vlan_ID value can be 1 through 4094, except
reserved VLANs (see Table 15-5 on page 15-21).
Router(config)# no spanning-tree vlan vlan_ID
root
Clears the root bridge configuration.
Step 2
Router(config)# end
Exits configuration mode.

Cisco 7609 Specifications

General

Brand	Cisco
Model	7609
Category	Network Router
Language	English