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 Multichannel DS3 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).

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, follow these steps:

In configuration mode, go to the following hierarchy level, depending on whether you are configuring a full T3 or T1 interface:
[edit]user@host# edit interfaces interface-name (t3-options | t1-options)
Configure the local loopback:
[edit interfaces interface-name (t3-options | t1-options)] user@host# set loopback local
The following is an example of the name for a T1 channel 0, group 0, on a Multichannel DS3 port for a channelized DS3 to DS0 interface:
[edit interfaces ds-2/1/0:0:0 t3-options]
Note: In order to configure T3 options on the Multichannel DS3, you configure the first logical interfaces: ds-2/1/0:0:0 t3-options.
The following is an example of the name for a T1 channel on a Multichannel DS3 port for a channelized DS3 to DS1 interface:
[edit interfaces t1-2/1/1:0 t1-options]
Verify the configuration:
user@host# show
For example:
[edit interfaces t1-2/1/1:0 t1-options]user@host# show loopback local;
Commit the configuration:
user@host# commit
For example:
[edit interfaces t1-2/1/1:0 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.