Users Guide

As soon as a BPDU is received on an STP port in a Loop-Inconsistent state, the port returns to a blocking state. If you disable
STP loop guard on a port in a Loop-Inconsistent state, the port transitions to an STP blocking state and restarts the max-age
timer.
Figure 134. STP Loop Guard Prevents Forwarding Loops
Configuring Loop Guard
Enable STP loop guard on a per-port or per-port channel basis.
The following conditions apply to a port enabled with loop guard:
• Loop guard is supported on any STP-enabled port or port-channel interface.
• Loop guard is supported on a port or port-channel in any spanning tree mode:
– Spanning Tree Protocol (STP)
– Rapid Spanning Tree Protocol (RSTP)
– Multiple Spanning Tree Protocol (MSTP)
– Per-VLAN Spanning Tree Plus (PVST+)
Spanning Tree Protocol (STP) 913