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Chapter 18
Configuring Optional Spanning-Tree Features
Figure 18-6
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 switch
(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 switch to Switch A, the root switch.
Figure 18-7
Switch C
Understanding EtherChannel Guard
You can use EtherChannel guard to detect an EtherChannel misconfiguration between the switch and a
connected device. A misconfiguration can occur if the switch interfaces are configured in an
EtherChannel, but the interfaces on the other device are not. A misconfiguration can also occur if the
channel parameters are not the same at both ends of the EtherChannel. For EtherChannel configuration
guidelines, see the
If the switch detects a misconfiguration on the other device, EtherChannel guard places the switch
interfaces in the error-disabled state, and displays an error message.
You can enable this feature by using the spanning-tree etherchannel guard misconfig global
configuration command.
OL-8915-03
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
"EtherChannel Configuration Guidelines" section on page
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
Understanding Optional Spanning-Tree Features
Switch B
L3
Switch B
(Designated bridge)
Added switch
Figure
18-7, BackboneFast is
33-9.
18-7
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