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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 50 Configuring Fallback Bridging Configuring Fallback Bridging

Fallback Bridging and Switch Stacks

When the stack master fails, a stack member becomes the new stack master by using the election process
described in Chapter 5, “Managing Switch Stacks.” The new stack master creates new VLAN-bridge
spanning-tree instance, which temporarily puts the spanning-tree ports used for fallback bridging into a
nonforwarding state. A momentary traffic disruption occurs until the spanning-tree states transition to
the forwarding state. All MAC addresses must be relearned in the bridge group.
Note If a stack master running the IP services feature set fails and if the newly elected stack master is running
the IP base feature set, the switch stack loses its fallback bridging capability.
If stacks merge or if a switch is added to the stack, any new VLANs that are part of a bridge group and
become active are included in the VLAN-bridge STP.
When a stack member fails, the addresses learned from this member are deleted from the bridge group
MAC address table.
For more information about switch stacks, see Chapter 5, “Managing Switch Stacks.”
Configuring Fallback Bridging
• Default Fallback Bridging Configuration, page 50-3
• Fallback Bridging Configuration Guidelines, page 50-4
• Creating a Bridge Group, page 50-4 (required)
• Adjusting Spanning-Tree Parameters, page 50-5 (optional)

Default Fallback Bridging Configuration

Tab le 50-1 Default Fallback Bridging Configuration
Feature Default Setting
Bridge groups None are defined or assigned to a port. No
VLAN-bridge STP is defined.
Switch forwards frames for stations that it has
dynamically learned
Enabled.
Spanning tree parameters:
• Switch priority
• Port priority
• Port path cost
• Hello BPDU interval
• Forward-delay interval
• Maximum idle interval
• 32768.
• 128.
• 10 Mb/s: 100.
100 Mb/s: 19.
1000 Mb/s: 4.
• 2 seconds.
• 20 seconds.
• 30 seconds.