Why is no trap reported after LBDT detects a loop on an S series switches

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After loopback detection is configured on an S series (except the S1700) or E series switch, an alarm is sent after a loop is detected only when the action is set to port-trap or trap using the loop-detection mode port-trap or loopback-detect action trap command.

Other related questions:
Can S series switches be configured not to take any action after a loop is detected
Huawei S series (except the S1700) and E series switches performs the configured default action after detecting a loop, that is, shutting down interfaces. The action can be changed but cannot be disabled. When the action is changed to trap, the switches only report traps and do not take any other action after detecting a loop. Command used to configure the action performed on an interface after LDT detects a loop: loop-detection mode { port-trap | port-blocking | port-nolearning | port-shutdown | port-quitvlan } Command used to configure the action performed on an interface after LBDT detects a loop: loopback-detect action { block | nolearn | shutdown | trap | quitvlan } Note: For S series switches, the port-quitvlan and quitvlan actions are supported in V200R002 and later versions.

How to configure loop detection on multiple ports on S series switches
Huawei S series (except the S1700) and E series switches support MAC address flapping detection, which can detect loops on multiple interfaces. You are advised to configure MAC address flapping detection on downlink interfaces and set the action to be taken after MAC address flapping occurs in alarm-only. If a loop occurs, an alarm will be sent to eSight, facilitating location of other faults. Enable MAC address flapping detection in VLANs. MAC address flapping detection in a maximum of 32 VLANs is supported. [Huawei] vlan 3 [Huawei-vlan3] loop-detect eth-loop block-time 30 retry-times 3 The alarm information consists of the interface name, VLAN ID, flapping time, and MAC address that flaps. Alarms can be generated consecutively. #Jan 1 2008 06:53:12-08:00 Huawei L2IFPPI/4/MFLPIFRESUME:OID1.3.6.1.4.1.2011.5.25.160.3.2 Loop does not exist in vlan 3, Interface Ethernet0/0/1 resumed, block-time is 30 for mac-flapping disappeared. #Jan 1 2008 06:52:22-08:00 Huawei L2IFPPI/4/MFLPIFBLOCK:OID1.3.6.1.4.1.2011.5.25.160.3.1 Loop exist in vlan 3, Interface Ethernet0/0/1 blocked, block-time is 30 for mac-flapping, Mac Address is 00e0-fc22-765a.

Will logs be generated when loops are detected on S series switch' interfaces where loopback detection is enabled
Logs and alarms will be generated after loops are detected on modular switches' interfaces where loopback detection is enabled. To view the related alarms, run the display trapbuffer command. Only alarms will be generated after loops are detected on interfaces of fixed switches (except S1700). To view the related alarms, run the display trapbuffer command.

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