Performing a loopback test on an Ethernet interface
If an Ethernet interface does not work correctly, you can perform a loopback test on it to identify the problem. An Ethernet interface in a loopback test does not forward data traffic.
Loopback tests include the following types:
Internal loopback test—Tests all on-chip functions related to Ethernet interfaces.
External loopback test—Tests the hardware of Ethernet interfaces. To perform an external loopback test on an Ethernet interface, connect a loopback plug to the Ethernet interface. The device sends test packets out of the interface, which are expected to loop over the plug and back to the interface. If the interface fails to receive any test packets, the hardware of the interface is faulty.
Configuration restrictions and guidelines
When you perform a loopback test on an Ethernet interface, follow these restrictions and guidelines:
On an administratively shut down interface (displayed as in ADM or Administratively DOWN state), you cannot perform an internal or external loopback test.
The speed, duplex, mdix-mode, and shutdown commands are not available during a loopback test.
During a loopback test, the Ethernet interface operates in full duplex mode. When a loopback test is complete, the port returns to its duplex setting.
Configuration procedure
To perform a loopback test on an Ethernet interface:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter Ethernet interface view. | interface interface-type interface-number | N/A |
3. Perform a loopback test. | loopback { external | internal } | By default, no loopback test is performed. The external keyword is not supported in the current version, and it is reserved for future support. |