Router A# show interface serial0
Serial is up line protocol is up, it is the first message that shows us that your serial port is configure properly. It is just possible when you have already given IP address, run no shutdown and configures some other command.
There are some possible errors messages may occur after the command is given.
Serial is up line protocol is down, it means that check your router encapsulation configuration.
Serial is down, line protocol is down.
- You have not given or define clock rate.
- Cable not connected or not working.
- Serial cable is not plug. Possible causes.
Serial is administratively down line protocol is down.It means that router is shut down by administrator manually for troubleshooting purpose.