To enable loopback on circuit, do the following steps:
NOTE: Loopback feature is not supported on VCG and Diamond circuits.
The user cannot enable loopback when the circuit is in Maintenance Mode.
Go to Configuration > Layer 1> Circuits menu and click Manage Circuits. The Manage Circuits page is displayed.
Select the desired circuit and click (View Details). Click Graphical View from the drop down. The graphical view of the circuit is displayed at the bottom of the page.
Select the desired node and click .
Click Toggle Loopback. The Enable Loopback window is displayed.
Select the port for which the loopback has to be enabled.
Click Apply. The Enable loopback command is sent successfully.
To disable loopback, do the following steps:
Select the desired node on the circuit on which loopback is enabled.
(View Details). Click Graphical View from the drop down. The graphical view of the circuit is displayed at the bottom of the page.
. 
