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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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Chapter44 Configuring Fallback Bridging
Monitoring and Maintaining Fallback Bridging

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.
This example shows how to disable spanning tree on a port in bridge gro up 10:
Switch(config)# interface gigabitethernet2/0/1
Switch(config-if)# bridge group 10 spanning-disabled
Monitoring and Maintaining Fallback Bridging
To monitor and maintain the network, use one or more of the privileged EXEC commands in Ta ble 44- 2:
To display the bridge-group MAC address table on a stack member, start a session from the stack master
to the stack member by using the session stack-member-number global configuration command. Enter
the show bridge [bridge-group] [interface-id | mac-address | verbose] privileged EXEC command at
the stack member prompt.
For information about the fields in these displays, see the Cisco IOS Bridging and IBM Networking
Command Reference, Volume 1 of 2, Release 12.2.
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.
Table44-2 Commands for Monitoring and Maintaining Fallback Bridging
Command Purpose
clear bridge bridge-group Removes any learned entries from the forwarding
database.
show bridge [bridge-group] group Displays details about the bridge group.
show bridge [bridge-group] [interface-id |
mac-address | verbose]
Displays MAC addresses learned in the bridge group.