Create a Loopback
You can create a physical loopback or configure a local loopback to help diagnose a suspected hardware problem. Creating a physical loopback is recommended because it allows you to test and verify the transmit and receive ports. If a field engineer is not available to create the physical loopback, you can configure a local loopback for the interface. The local loopback creates a loopback internally in the Physical Interface Card (PIC).
Create a Physical Loopback
Action
To create a physical loopback at the port, connect the transmit port to the receive port.
Meaning
When you create and test a physical loopback, you are testing the transmit and receive ports of the PIC. This action is recommended if a field engineer is available to create the physical loop as it provides a more complete test of the PIC.
Configure a Local Loopback
Action
To configure a local loopback without physically connecting the transmit port to the receive port, follow these steps:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name t3-options
- Configure the loopback:[edit interfaces interface-name t3-options]user@host# set loopback local
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0 t3-options]user@host# show loopback local; - Commit the change:user@host# commit
For example:
[edit interfaces t3-1/0/0 t3-options]user@host# commit commit complete
Meaning
When you create a local loopback, you create an internal loop on the interface being tested. A local loopback loops the traffic internally on that PIC. A local loopback tests the interconnection of the PIC but does not test the transmit and receive ports.
 | Note: Remember to delete the loopback statement after completing the test. |
