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Configuration Guide - Ethernet Switching

S7700 and S9700 V200R011C10

This document describes the configuration of Ethernet services, including configuring link aggregation, VLANs, Voice VLAN, VLAN mapping, QinQ, GVRP, MAC table, STP/RSTP/MSTP, SEP, and so on.
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Configuring an Action Taken After a Loop Is Detected

Configuring an Action Taken After a Loop Is Detected


By default, when a loop on an interface or the network connected to the interface, the device does not take any action. To notify users of network connections and configurations when a loop occurs on an interface, and minimize the impact of loops on the device and entire network, configure an action taken on the problematic interface.

The device provides the following actions after LDT detects a loop:
  • Trap: The device reports a trap to the NMS and records a log, but does not take any action on the interface.
  • Block: The device isolates an interface where a loop occurs from other interfaces, and can forward only BPDUs.
  • No learning: The interface is disabled from learning MAC addresses.
  • Shutdown: The device shuts down the interface.
  • Quitvlan: The interface is removed from the VLAN where a loop occurs.

For details about the actions, see Action Taken After a Loop Is Detected. You can configure one of the actions according to actual networking.


  1. Run system-view

    The system view is displayed.

  2. Run snmp-agent trap enable

    Or, run snmp-agent trap enable feature-name ldttrap

    The trap function is enabled for LDT. This function allows the device to send traps of LDT.

    By default, the trap function is disabled for LDT.

  3. Run interface interface-type interface-number

    The interface view is displayed.

  4. Run loop-detection mode { port-trap | port-blocking | port-nolearning | port-shutdown | port-quitvlan }

    An action taken after a loop is detected is configured.

    By default, an interface is shut down after LDT detects a loop.

    • When a loop occurs on the network-side interface where the block or shutdown action is configured, all services on the device are interrupted. Do not deploy LDT on the network-side interface.

    • The Quitvlan action cannot be used with such functions as GVRP, HVRP and the function of removing an interface from the VLAN where MAC address flapping occurs. These functions dynamically delete an interface from a VLAN.

Updated: 2019-10-18

Document ID: EDOC1000178310

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