Diagnosing Serial Link Symptoms with the show interface CommandThere are many different types of encapsulations and protocols that can run over serial links. This can create many possible configuration problems. Most serial link problems unrelated to hardware are caused by a mismatched configuration on either side of the serial link. Both ends of a serial link must use the same encapsulation types, speed, and protocol types. You can use the show interface command to reveal information that will help you in troubleshooting serial links. The output of the show interface command gives you a variety of information about each interface's status.
Each of the following sub-sections discusses a problem that can be revealed in the output of the show interface command, and discusses some potential causes for those problems. Here are the serial interface symptoms diagnosed from the show interface command in these sections:
Interface Is Administratively Down; Line Protocol Is DownThe Interface Is Administratively Down; Line Protocol Is Down error shown by the router indicates that a manual change to the router's configuration has been made. Here are some potential causes:
Interface Is Down; Line Protocol Is DownThe Interface Is Down; Line Protocol Is Down error shown by the router indicates that the line is not making a connection and the protocols configured are not sending valid keepalive messages. This can be an indicator of many types of problems. To troubleshoot this problem, use the following steps:
Interface Is Up; Line Protocol Is DownTo troubleshoot this problem, use the following steps:
Keepalive Sequencing Not IncrementingThe Keepalive Sequencing Not Incrementing error is usually an indicator of a line problem, meaning that the configured protocols and the router are not receiving keepalive messages. To troubleshoot this problem, use the following steps:
Interface Is Up; Line Protocol Is Up (Looped)To troubleshoot this problem, use the following step:
Incrementing Carrier Transition CounterAn increasing Carrier Transition Counter on a serial interface shown by the show interface command output indicates that the interface is not staying active. To troubleshoot this problem, use the following steps:
Incrementing Interface ResetsWhen the Interface Resets counter is incrementing, this means the interface is performing the equivalent of reboot. To troubleshoot this problem, use the following steps:
Input Drops, CRC, and Framing ErrorsIncreasing line drops, CRC, and framing errors can be an indication of a serious problem. When these errors occur, sent data is not making it to its destination. To troubleshoot this problem, use the following steps:
|