Cisco Catalyst 2950 Software Configuration Manual page 293

Chapter 12 Configuring Optional Spanning-Tree Features
switchover takes approximately 30 seconds, twice the Forward Delay time if the default Forward Delay
time of 15 seconds is set.
the failure of link L1.
Figure 12-8 BackboneFast Example After Indirect Link Failure
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 12-9 Adding a Switch in a Shared-Medium Topology
Switch C
78-11380-04
Figure 12-8
L1
Link failure
L2
BackboneFast transitions port
through listening and learning
states to forwarding state.
Switch C
Switch A
(Root)
Blocked port
Understanding Optional Spanning-Tree Features
shows how BackboneFast reconfigures the topology to account for
Switch B
L3
Switch B
(Designated bridge)
Added switch
Catalyst 2950 Desktop Switch Software Configuration Guide
Figure 12-9, BackboneFast is
12-11