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Cisco IOS in a Nutshell, 2nd Edition by James Boney

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Name

down-when-looped — interface

Synopsis

down-when-looped
no down-when-looped

Configures

Loopback detection

Default

Disabled

Description

This command tells the interface to go down when a loopback is detected. The default behavior is for the interface to remain up when the device is placed in loopback, so you can place a DCE device such as a CSU/DSU in loopback and ping the interface. This allows you to test the cable between the router and the DCE device.

Use the no form of this command to disable this behavior. If this command is given, the interface shuts down when the DCE device (CSU/DSU) is placed in loopback mode.

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