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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter48 Configuring Fallback Bridging
Configuring Fallback Bridging

Changing the Maximum-Idle Interval

If a switch does not receive BPDUs from the root switch within a specified interval, it recomputes the
spanning-tree topology.
Beginning in privileged EXEC mode, follow these steps to change the maximum-idle interval (maximum
aging time). This procedure is optional.
To return to the default setting, use the no bridge bridge-group max-age global configuration command.
This example shows how to change the maximum-idle interval to 30 seconds in bridge group10:
Switch(config)# bridge 10 max-age 30
Disabling the Spanning Tree on an Interface
When a loop-free path exists between any two switched subnetworks, you can prevent BPDUs generated
in one switching subnetwork from impacting devices in the other switching subnetwork, yet still permit
switching throughout the network as a whole. For example, when switched LAN subnetworks are
separated by a WAN, BPDUs can be prevented from traveling across the WAN link.
Beginning in privileged EXEC mode, follow these steps to disable spanning tree on a port. This
procedure is optional.
To re-enable spanning tree on the port, use the no bridge-group bridge-group spanning-disabled
interface configuration command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 bridge bridge-group max-age seconds Specify the interval that the switch waits to hear BPDUs from the root
switch.
For bridge-group, specify the bridge group number. The range is 1
to 255.
For seconds, enter a number from 6 to 200. The default is 30.
Step3 end Return to privileged EXEC mode.
Step4 show running-config Verify your entry.
Step5 copy running-config startup-config (Optional) Save your entry in the configuration file.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the port, and enter interface configuration mode.
Step3 bridge-group bridge-group
spanning-disabled
Disable spanning tree on the port.
For bridge-group, specify the bridge group number. The range is 1
to 255.
Step4 end Return to privileged EXEC mode.
Step5 show running-config Verify your entry.
Step6 copy running-config startup-config (Optional) Save your entry in the configuration file.