V-273679

Discussion

The STP loop Detect feature provides additional protection against STP loops. An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. In its operation, STP relies on continuous reception and transmission of BPDUs based on the port role. The designated port transmits BPDUs, and the nondesignated port receives BPDUs. When one of the ports in a physically redundant topology no longer receives BPDUs, the STP conceives that the topology is loop-free. Eventually, the blocking port from the alternate or backup port becomes a designated port and moves to a forwarding state. This situation creates a loop. The loop detect feature makes additional checks. If BPDUs are not received on a nondesignated port and loop detect is enabled, that port is moved into the STP loop-inconsistent blocking state.

Check Content

Review the switch configuration to verify that STP Loop Detect is enabled.

Verify:
ICX7150-24P Switch#show run
!
vlan 10 by port
 tagged ethernet 1/1/1 to 1/1/2 ethernet 1/1/5 ethernet 1/1/7 ethernet 1/1/9 ethernet 1/1/11 
 spanning-tree
 loop-detection
!

If STP Loop Detect is not configured globally or on nondesignated STP ports, this is a finding.