Configuration Notes and Constraints
When configuring loopback detection, consider the following points:
The loopback detection message is sent in the native VLAN. When a loopback detection message is received, the device considers the source MAC address to determine if the message was sent from this device, without considering the VLAN tag.
Loopback detection can be enabled on a physical interface or a Link Aggregation Group (LAG) interface but cannot be enabled on the member interfaces of a LAG.
To enable the loopback detection function, users need to enable loopback detection BOTH globally and at the per-interface level.
Loopback detection is not supported in Multi-Chassis Link Aggregation (MLAG) scenarios.
Configuring Loopback Detection
Step 1 Enable loopback detection function globally.
set protocols loopback-detection enable <true | false>
Step 2 Enable loopback detection function on a specific interface.
set protocols loopback-detection interface <interface-name> enable <true | false>
Step 3 (Optional) Configure the loopback detection message transmission period.
set protocols loopback-detection message-interval <message-interval>
Step 4 (Optional) Clear the err-disable state of the loopback-detection interface.
run clear loopback-detection interface {<interface-name> | all}
Step 5 Commit the configuration.
commit
Step 6 View the configuration information and status information of loopback detection.
run show loopback-detection
Example for Configuring Loopback Detection
Networking Requirements
Figure 1. Loopback Detection Configuration Example
As shown in Figure 1, if there is a loop in the network connected to interface ge-1/1/1 of the device Switch, it will cause a broadcast storm, and communication on the Switch and the entire network may be affected.
Users hope to detect loops in the downstream network connected to the Switch and reduce the impact of the loop to the networks by blocking the downlink interface. Users can achieve this by enabling loopback detection function on ge-1/1/1 of the Switch. Once a loop is detected, interface state of ge-1/1/1 will be set to err-disable, resulting in the disconnection of the interface. This action helps to reduce the impact of the loop on the device and the network.
Procedure
Step 1 Enable loopback detection function globally.
admin@Switch# set protocols loopback-detection enable true
Step 2 Enable loopback detection function on a specific interface.
admin@Switch# set protocols loopback-detection interface ge-1/1/1 enable true
Step 3 Commit the configurations.
admin@Switch# commit
Step 4 View the configuration information and status information of loopback detection.
admin@Switch# run show loopback-detection Loopback-detection: enabled message-interval: 30s Interface LBD Tx Status From_Port ---------- ----------- ------------ ----------- ge-1/1/1 true LoopDetected ge-1/1/1 ge-1/1/2 false Normal ...... admin@Switch# run show interface gigabit-ethernet xe-1/1/1 Physical interface: ge-1/1/1, Enabled, error-discard True(LBD), Physical link is Down Interface index: 73, QSFP+ type: 40G_BASE_SR4, Mac Learning Enabled Port mode: access Description: …….
From the show result, we can see that,
Status of interface ge-1/1/1 is “LoopDetected” and “error-discard True(LBD), Physical link is Down”, indicating a loop is detected and the interface is disabled.
When a loopback is detected, the field From_Port indicates the sending interface of loopback detection packets.