Cisco 7609-S Software Configuration Guide - Page 322

Understanding How EtherChannel Guard Works Chapter 21 Configuring Optional STP Features Figure 21-4 BackboneFast Example After Indirect Link Failure Switch A (Root) Switch B L1 Link failure L2 L3 Switch C BackboneFast transitions port through listening and learning states to forwarding state 11244 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 Switch A (Root) Switch C Blocked port Switch B (Designated Bridge) Added switch 11245 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. 21-6 Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX OL-4266-08