Enabling Backbonefast - Cisco Catalyst 4500 Series Configuration Manual

Chapter 23 Configuring Optional STP Features
Figure 23-5
Figure 23-5
Switch A
(Root)
If a new switch is introduced into a shared-medium topology as shown in
not activated, because the inferior BPDUs did not come from the recognized designated bridge
(Switch B). The new switch begins sending inferior BPDUs that say it is the root switch. However, the
other switches ignore these inferior BPDUs, and the new switch learns that Switch B is the designated
bridge to Switch A, the root switch.
Figure 23-6
Switch C

Enabling BackboneFast

For BackboneFast to work, you must enable it on all switches in the network. BackboneFast is supported
Note
for use with third-party switches but it is not supported on Token Ring VLANs.
To enable BackboneFast, perform this task:
OL-25340-01
shows how BackboneFast reconfigures the topology to account for the failure of link L1.
BackboneFast after Indirect Link Failure
L1
L2
Blocked port
Switch C
Adding a Switch in a Shared-Medium Topology
Switch A
(Root)
Blocked port
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Switch B
L3
Switch B
(Designated Bridge)
Added switch
Enabling BackboneFast
Figure 23-6, BackboneFast is
23-15