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AR500, AR510, and AR530 V200R007 CLI-based Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring transparent bridge, MAC table, link aggregation, VLANs, STP/RSTP/MSTP, and so on.The document provides the configuration procedures and configuration examples to illustrate the service configuration methods and application scenario.
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Configuring Loop Protection on an Interface

Configuring Loop Protection on an Interface


On a network running MSTP, a switching device maintains the root port status and status of blocked ports by receiving BPDUs from an upstream switching device. If the switching device cannot receive BPDUs from the upstream device because of link congestion or unidirectional-link failure, the switching 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 switching may cause network loops, which can be mitigated by configuring loop protection.

If the root port or alternate port does not receive BPDUs from the upstream device for a long time, the switch enabled with loop protection sends a notification to the NMS. If the root port is used, the root port enters the Discarding state and becomes the designated port. If the alternate port is used, the alternate port keeps blocked and becomes the designated port. In this case, loops will not occur. After the link is not congested or unidirectional link failures are rectified, the port receives BPDUs for negotiation and restores its original role and status.

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

Perform the following steps on the root port and alternate port on a switching device in an MST region.


  1. Run:


    The system view is displayed.

  2. Run:

    interface interface-type interface-number

    The Ethernet interface view is displayed.

  3. Run:

    stp loop-protection

    Loop protection for the root port is configured on the switching device.

    By default, loop protection is disabled.

    Root protection and loop protection cannot be configured simultaneously.

Updated: 2019-05-25

Document ID: EDOC1000097279

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