Line Loopback Detection

This section describes how to configure line loopback detection.

Context

When a loop occurs on a network, broadcast, multicast, and unknown unicast packets are repeatedly transmitted on the network. This wastes network resources or even causes service interruption on the entire network. To allow the device to detect loops on a Layer 2 network in a timely manner and prevent the network from being severely affected by loops, configure loopback detection. Loopback detection enables the device to periodically send loopback detection packets to detect loops. When a loop is detected on an interface, the device shuts down or blocks the interface to eliminate the loop. The interface can be restored when the device detects that the loop on the interface is eliminated.

Procedure

Choose Configuration to open the Configuration page. Click LBDT to open the LBDT page.

Table 1 describes parameters on the loopback detection configuration page.

**Table 1** Parameters on the loopback detection configuration page
Parameter		Description
Enable (Blocking Interface)		Enable loopback detection on an interface and set the action to block. When a loop is detected, the device blocks the interface and forwards only BPDUs.
Enable (Shutdown Interface)		Enable loopback detection on an interface and set the action to shutdown. When a loop is detected, the device shuts down the interface.
Disable		Disable loopback detection on the interface.

Select an interface that you want to configure.
Perform either of the following operations:
- Click the interface icon to select a single interface.
- Drag the mouse to select consecutive interfaces in a batch.
- Select an LPU and all interfaces on the LPU.
Click Enable (Blocking Interface) or Enable (Shutdown Interface) to enable loopback detection on an interface and set the action taken when a loop is detected.
By default, loopback detection is disabled on an interface.

NOTE:
If Enable (Shutdown Interface) is selected, the interface is shut down when a loop is detected. The shutdown interface can be restarted in Interface Setting > Enable/Disable Interface. For details, see Enable/Disable Interface.
Check the configuration.
If the loopback detection status is displayed on all interfaces that need to be enabled with loopback detection.

NOTE:
After line loopback detection is enabled, the system detects loops after about 5s. After 5s, click

to view the interface status.