11-7
Cisco Systems IntelligentGigabit Ethernet Switch Modules for the IBM BladeCenter, Software Configuration Guide
24R9746
Chapter11 Configuring Optiona l Spanning-Tree Features
Understanding Optional Spanning-Tree Features
Figure11-6 BackboneFast Example After Indirect Link Failure
If a new switch is introduced into a shared-medium topology as shown in Figure11-7, BackboneFast is
not activated because the inferior BPDUs did not come from the re cognized 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 SwitchA, the root switch.
Figure11-7 Adding a Switch in a Shared-Medium Topology
L1
L2 L3
Switch C
Switch A
(Root) Switch B
Link failure
44964
BackboneFast changes port
through listening and learning
states to forwarding state.
Switch A
(Root)
Switch C Switch B
(Designated bridge)
Added switch
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Blocked port