The output from the show interface command can be used to detect common media issues. One of the most important parts of this output is the display of the line and data link protocol status. Figure 1 indicates the summary line to check the status of an interface.

The first parameter (FastEthernet0/1 is up) refers to the hardware layer and, essentially, reflects whether the interface is receiving the carrier detect signal from the other end. The second parameter (line protocol is up) refers to the data link layer and reflects whether the data link layer protocol keepalives are being received.

Based on the output of the show interface command, possible problems can be fixed as follows:

Figure 2 shows an example of show interface command output. The example shows counters and statistics for the FastEthernet0/1 interface.

Some media errors are not severe enough to cause the circuit to fail, but do cause network performance issues. Figure 3 explains some of these common errors which can be detected with using the show interface command.

“Input errors” is the sum of all errors in datagrams that were received on the interface being examined. This includes runts, giants, CRC, no buffer, frame, overrun, and ignored counts. The reported input errors from the show interface command include the following:

“Output errors” is the sum of all errors that prevented the final transmission of datagrams out of the interface that is being examined. The reported output errors from the show interface command include the following: