Configuring Loop Protection on an Interface

The loop protection function suppresses the loops caused by link congestion.

Context

On a network running Multiple Spanning Tree Protocol (MSTP), a device maintains the root port status and status of blocked ports by receiving Bridge Protocol Data Units (BPDUs) from an upstream device. If the device cannot receive BPDUs from the upstream because of link congestion or unidirectional-link failure, the device re-selects a root port. The original root port becomes a designated port and the original blocked ports change to the Forwarding state. This may cause network loops. To address such a problem, configure loop protection.

After loop protection is configured, if the root port or alternate port does not receive BPDUs from the upstream device, the root port is blocked and the device notifies the NMS that the port enters the Discarding state. The blocked port remains in the Blocked state and no longer forwards packets. This prevents loops on the network. The root port restores the Forwarding state after receiving new BPDUs.

An alternate port is a backup port of a root port. If a device has an alternate port, you need to configure loop protection on both the root port and the alternate port.

Do as follows on a root port and an alternate port on a device in an MST region:

Procedure

Run system-view
The system view is displayed.
Run interface interface-type interface-number
The view of the Ethernet interface participating in STP calculation is displayed.

The following configuration can be configured both on a Layer 2 interface and a Layer 3 interface.
(Optional) Run stp binding process process-id
The port is bound to an MSTP process.

This step is performed only when the interface needs to be bound to an MSTP process with a non-zero ID. If the interface belongs to process 0, skip this step.
Run stp loop-protection
Loop protection for the root port is configured on the device.
Run commit
The configuration is committed.