Create a Loopback

Purpose

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 T1 port. 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).

1. Create a Physical Loopback
2. Configure a Local Loopback

Create a Physical Loopback

Action

To create a physical loopback at the T1 port, connect a T1 loopback plug to the T1 port. You can make a T1 loopback plug by connecting pin 1 to pin 4 and pin 2 to pin 5 on an RJ-48 plug.

Meaning

When you create and test a physical loopback, you are testing the T1 port. 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:

1. In configuration mode, go to the following hierarchy level:

   [edit]

   user@host# edit interfaces interface-name t1-options

2. Configure the loopback:

   [edit interfaces interface-name t1-options]

   user@host# set loopback local

3. Verify the configuration:

   user@host# show

   For example:

   [edit interfaces t1-1/3/0 t1-options]

   user@host# show

   loopback local;

4. Commit the change:

   user@host# commit

   For example:

   [edit interfaces t1-1/3/0 t1-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.