down-when-looped

Use the down-when-looped interface configuration command to configure an interface to inform the system it is down when loopback is detected.

This command is valid for HDLC or PPP encapsulation on serial and HSSI interfaces.

Backup Interfaces

When an interface has a backup interface configured, it is often desirable that the backup interface be enabled when the primary interface is either down or in loopback. By default, the backup is only enabled if the primary interface is down. By using the down-when-looped command, the backup interface will also be enabled if the primary interface is in loopback.

Testing an Interface with the Loopback Command

If testing an interface with the loopback command, or by placing the DCE into loopback, down-when-looped should not be configured; otherwise, packets will not be transmitted out the interface that is being tested.

Examples

The following example configures interface serial 0 for HDLC encapsulation. It is then configured to let the system know that it is down when in loopback mode.

interface serial0

 encapsulation hdlc

 down-when-looped