Cisco 7604 User Manual

21-6
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 21 Configuring Optional STP Features
Understanding How EtherChannel Guard Works
Figure 21-4 BackboneFast Example After Indirect Link Failure
If a new network device is introduced into a shared-medium topology as shown in Figure 21-5,
BackboneFast is not activated because the inferior BPDUs did not come from the recognized designated
bridge (Switch B). The new network device begins sending inferior BPDUs that indicate that it is the
root bridge. However, the other network devices ignore these inferior BPDUs and the new network
device learns that Switch B is the designated bridge to Switch A, the root bridge.
Figure 21-5 Adding a Network Device in a Shared-Medium Topology
Understanding How EtherChannel Guard Works
EtherChannel guard detects a misconfigured EtherChannel where interfaces on the Cisco 7600 series
router are configured as an EtherChannel while interfaces on the other device are not, or not all the
interfaces on the other device are in the same EtherChannel.
In response to misconfiguration detected on the other device, EtherChannel guard puts interfaces on the
Cisco 7600 series router into the errdisabled state.
L1
L2 L3
Switch C
Switch A
(Root)
Switch B
Link failure
11244
BackboneFast transitions port
through listening and learning
states to forwarding state
Switch A
(Root)
Switch C
Switch B
(Designated Bridge)
Added switch
11245
Blocked port

Cisco 7604 Specifications

General

Brand	Cisco
Model	7604
Category	Network Router
Language	English