Diagnose a Suspected Circuit Problem

When you suspect a circuit problem, it is important to work with the transport-layer engineer to resolve the problem. The transport-layer engineer may ask you to create a loop from the router to the network, or the engineer may create a loop to the router from various points in the network.

To diagnose a suspected circuit problem, follow these steps:

1. Create a Loop from the Router to the Network
2. Create a Loop to the Router from Various Points in the Network

Create a Loop from the Router to the Network

Purpose

Creating a loop from the router to the network allows the transport-layer engineer to test the router from various points in the network. This helps the engineer isolate where the problem is located.

Action

To create a loop from the router to the network, follow these steps:

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

   [edit]

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

2. Configure remote loopback:

   [edit interfaces interface-name t1-options]

   user@host# set loopback remote

3. Verify the configuration:

   user@host# show

   For example:

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

   user@host# show

   loopback remote;

4. Commit the change:

   user@host# commit

   For example:

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

   user@host# commit

   commit complete

Meaning

This command loops any traffic from the network back into the network.

Create a Loop to the Router from Various Points in the Network

Purpose

The transport-layer engineer creates a loop to the router from various points in the network. You can then perform tests to verify the connection from the router to that loopback in the network.

Action

After the transport-layer engineer has created the loop to the router from the network, you must verify the connection from the router to the loopback in the network. Follow Step 2 through Step 8 in Diagnose a Suspected Hardware Problem with a T1 Interface. Keep in mind that any problems encountered in the test indicate a problem with the connection from the router to the loopback in the network.

By performing tests to loopbacks at various points in the network, you can isolate the source of the problem.