Cisco IE-3000-8TC User Manual

20-7
Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 20 Configuring Optional Spanning-Tree Features
Understanding Optional Spanning-Tree Features
Figure 20-6 BackboneFast Example After Indirect Link Failure
If a new switch is introduced into a shared-medium topology as shown in Figure 20-7, BackboneFast is
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 20-7 Adding a Switch in a Shared-Medium Topology
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
“EtherChannel Configuration Guidelines” section on page 38-9.
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.
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
44965
Blocked port

Cisco IE-3000-8TC Specifications

General

Brand	Cisco
Model	IE-3000-8TC
Category	Switch
Language	English