show controllers serial Provides information on the interface status, cable types, missed datagrams, overruns, bad encapsulated frames , memory errors, underruns, clock rate, and bit errors.
The "Interface Is Down; Line Protocol Is Down" troubleshooting steps:
Check the cabling.
Check that a carrier signal from a local provider exists.
Consider a hardware failure on the interface or CSU/DSU.
The "Interface Is Up; Line Protocol Is Down" troubleshooting steps:
Check the interface configurations.
Check with the local provider to verify that it is not having line issues.
debug serial interface Displays real-time information about serial interface events.
clear counters serial Clears the counters for the serial interface.
