Cisco Catalyst 2950 Software Configuration Manual page 319

Chapter 15 Configuring Optional Spanning-Tree Features
Figure 15-8
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 indicate 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 15-9
Switch C
78-11380-12
BackboneFast Example After Indirect Link Failure
L1
Link failure
L2
BackboneFast changes port
through listening and learning
states to forwarding state.
Switch C
Adding a Switch in a Shared-Medium Topology
Switch A
(Root)
Blocked port
Understanding Optional Spanning-Tree Features
Switch B
L3
Switch B
(Designated bridge)
Added switch
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
Figure 15-9, BackboneFast is
15-11