Configuring Internal Loopback Detection

Context

When testing some special functions, for example, locating an Ethernet fault, you need to enable loopback detection on Ethernet interfaces to check whether the interfaces are working properly. After loopback detection is enabled on an Ethernet interface, the interface is in Up state if it works properly, and is in Down state if it fails.

In internal loopback detection, a packet from an interface is sent back to the interface through the internal chip. Internal loopback detection checks whether the connection between the interface and internal chip is normal. In external loopback detection, a packet from an interface is sent back to the interface through a loopback connector. External loopback detection checks whether the interface properly sends and receives packets. Currently, the device supports only internal loopback detection. As shown in Figure 1, after internal loopback detection is enabled on GE0/0/1, the chip generates some test packets, and these test packets are sent back to the chip through GE0/0/1. The internal loopback detection is complete.

Figure 1 Internal loopback detection

After internal loopback detection is enabled on an interface, other functions may be affected. After the test is complete, run the undo loopback command to disable loopback detection. The original configuration on the interface is then restored.

Procedure

Run system-view

The system view is displayed.
Run interface interface-type interface-number

The interface view is displayed.
Run loopback internal

Internal loopback detection is configured on the Ethernet interface.

By default, internal loopback detection is disabled on an Ethernet interface.

Verifying the Configuration

Run the display interface [ interface-type [ interface-number ] ] command in any view or the display this interface command in the interface view to check the current interface status. Check the Loopback field in the command output.

After loopback detection is enabled on an interface, the Speed field in the display this interface command output indicates the configured interface rate or the rate of the installed optical module, copper module, or network cable, and the Bandwidth field in the display interface ethernet brief command output indicates the actual interface rate.