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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
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Chapter44 Configuring Fallback Bridging
Configuring Fallback Bridging
Figure44-1 Fallback Bridging Network Example

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 St acks.” The new stack master creates new VLAN-bridge
spanning-tree instance, which temporarily puts the spanning-tree ports used for fallba ck 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 bri dge 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 m ember are deleted from the bridge group
MAC address table.
For more information about switch stacks, see Chapter5, “Managing Switch Stacks.”
Configuring Fallback Bridging
These sections contain this configuration information:
•Default Fallback Bridging Configuration, page 44-4
•Fallback Bridging Configuration Guidelines, page 44-4
•Creating a Bridge Group, page 44-4 (required)
•Adjusting Spanning-Tree Parameters, page 44-6 (optional)
101240
Host A
Host C
SVI 1172.20.128.1 172.20.129.1
Layer 3 switch Routed port
172.20.130.1
SVI 2
VLAN 20
Host B
VLAN 30