Observe the status and protocol states for the serial interfaces. If the routers are properly configured, explain what could cause the following conditions.

Question

1. Serial 0/0/0 is up, line protocol is up
2. Serial 0/0/0 is down, line protocol is down (DTE mode)
3. Serial 0/0/0 is up, line protocol is down (DTE mode)
4. Serial 0/0/0 is up, line protocol is down (DCE mode)
5. Serial 0/0/0 is administratively down, line protocol is down

Answer 1

1. This is the proper setting for a fully configured serial interface.
2. Typically indicates that the router is not sensing a CD signal (that is, CD is not active).
Telephone company problem—Line is down or line is not connected to the CSU/DSU
Faulty or incorrect cabling
Hardware failure (CSU/DSU)
3. Local or remote router is misconfigured.
Keepalives are not being sent by remote router.
Leased-line or other carrier service problem—Noisy line or misconfigured or failed switch.
Timing problem on the cable (SCTE not set on CSU/DSU).
Failed local or remote CSU/DSU.
Router hardware failure (local or remote).
4. Missing clockrate interface configuration command.
DTE device does not support or is not set up for SCTE mode.
Failed remote CSU or DSU.
Failed or incorrect cable.
Router hardware failure.
5. Router configuration includes the shutdown interface configuration command.