Chapter 26
Configuring Optional STP Features
Figure 26-9
Switch A
(Root)
If a new switch is introduced into a shared-medium topology as shown in
is 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 26-10
Switch C
Enabling BackboneFast
Note
For BackboneFast to work, you must enable it on all switches in the network. BackboneFast is supported
for use with third-party switches but it is not supported on Token Ring VLANs.
To enable BackboneFast, perform this task:
BackboneFast after Indirect Link Failure
L1
L2
Switch C
Adding a Switch in a Shared-Medium Topology
Switch A
(Root)
Blocked port
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Switch B
L3
Blocked port
Added switch
Enabling BackboneFast
Figure
26-10, BackboneFast
Switch B
(Designated Bridge)
26-23