Configure single-interface loopback detection on S series switch

How to configure single-interface loopback detection on S series switches (except S1700)?
Among external loopback detection, only single-interface loopback detection is supported on switches. After external loopback detection is enabled on an Ethernet interface of a switch, the switch periodically checks whether external loopback occurs on each Ethernet interface. If an S series switch finds that external loopback occurs on an Ethernet interface, by default, it blocks the interface when it runs a version earlier than V200R001 or shuts down the interface when it runs V200R001 or a later version. If an E series switch finds that external loopback occurs on an Ethernet interface, by default, it shuts down the interface.

1. Application Scenario
In actual networking, single-interface loopback detection is often used on a downlink interface of a newly deployed or added access switch. You are advised to set the action taken after loopback is detected to block.

2. Configuration Procedure
Enable loopback detection globally. This function will then be enabled on all interfaces simultaneously.

[Huawei] loopback-detect enable
Modular switches running V200R001 or later support loopback detection in a maximum of eight VLANs.
Fixed switches running V100R005 or later support loopback detection in a maximum of eight VLANs.
E series switches support loopback detection in a maximum of eight VLANs.
The following example describes how to configure loopback detection on a fixed switch:
[Huawei-Ethernet0/0/1] loopback-detect packet vlan 20 21 22 23 24 25 26 27
[Huawei-Ethernet0/0/1] loopback-detect action block

Among E series switches, modular switches running V200R001 and fixed switches running V100R005 or later save loopback alarm information in the trap buffer, and the alarm information can also contain information about the VLAN in which loopback is detected.

Alarm information is as follows:
#Jan 1 2008 06:43:54-08:00 Quidway LDT/4/Porttrap:OID1.3.6.1.4.1.2011.5.25.174.3.3 Loopback does exist on interface(5) Ethernet0/0/1 ( VLAN 20 ) , loopback detect status: 4.(1:normal; 2:block;3:shutdown; 4:trap; 5:nolearn)

3. Precautions
Loopback detection will consume some system resources. After deploying or adding access switches, run the undo loopback-detect enable command to disable this function.

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