5.7 Monitoring the ISDN Interface
5.7.1 The show interface bri command

The show interface bri command displays information about the BRI D channel or about one or more B channels, provided that your router is a TE1 (has a native BRI), as shown in the Figure.

Note: Click on the topology to view the command outputs.

If your router acts as a TEI (has a native BRI), use the show interface bri command to monitor the interface and the first B channel. If, on the other hand, the router is a TE2 (has an external terminal adapter), use the show interface serial command.

Why Is the Router Spoofing?
The word spoofing indicates that the line is not necessarily up, but the dialer is forcing the line to masquerade as up. Spoofing is a state to allow DDR to work (other states are up, down, and so on). The interface dials on demand in response to the packets being routed to it. But because no packets are routed to down interfaces, the interface must pretend to be up (spoof), so that packets will be routed to it when it is not connected. By default, a router removes any routes pointing to down interfaces from its routing table. DDR interfaces with BRI remain in spoofing state, even when one or both B channels are up.

The command to display the B1 information is show interface bri 0 1 2. The Figure  displays information on both B channels.