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Catalyst 3750 Switch Software Configuration Guide
78-16180-02
Chapter 38 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 group 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 Table 38-2:
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, refer to the Cisco IOS Bridging and IBM Networking
Command Reference, Volume 1 of 2, Release 12.2.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Specify the port, and enter interface configuration mode.
Step 3
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.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config Verify your entry.
Step 6
copy running-config startup-config (Optional) Save your entry in the configuration file.
Table 38-2 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.
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