Cisco Catalyst 2950 Software Manual page 224

Understanding Advanced STP 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 9-11 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 9-12 Adding a Switch in a Shared-Medium Topology
Switch C
Catalyst 2950 Desktop Switch Software Configuration Guide
9-18
Figure 9-11
L1
Link failure
L2
BackboneFast transitions port
through listening and learning
states to forwarding state.
Switch C
Switch A
(Root)
Blocked port
shows how BackboneFast reconfigures the topology to account for
Switch B
L3
Switch B
(Designated bridge)
Added switch
Chapter 9 Configuring STP
Figure 9-12, BackboneFast is
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