Enabling loop guard
By continuing to receive BPDUs from the upstream device, a device can maintain the state of the root port and blocked ports. However, link congestion or unidirectional link failures might cause these ports to fail to receive BPDUs from the upstream devices. In this situation, the device reselects the following port roles:
Those ports in forwarding state that failed to receive upstream BPDUs become designated ports.
The blocked ports transit to the forwarding state.
As a result, loops occur in the switched network. The loop guard feature can suppress the occurrence of such loops.
The initial state of a loop guard-enabled port is discarding in every MSTI. When the port receives BPDUs, it transits its state. Otherwise, it stays in the discarding state to prevent temporary loops.
Do not enable loop guard on a port that connects user terminals. Otherwise, the port stays in the discarding state in all MSTIs because it cannot receive BPDUs.
On a port, the loop guard feature is mutually exclusive with the root guard feature or the edge port setting.
Configure loop guard on the root port and alternate ports of a device.
To enable loop guard:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter Layer 2 Ethernet interface or Layer 2 aggregate interface view. | interface interface-type interface-number | N/A |
3. Enable the loop guard feature for the ports. | stp loop-protection | By default, loop guard is disabled. |