Troubleshooting Serial Lines
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of incoming packets on the interface. Because it is a counter, it will reach a
maximum value, and then reset. The next line displays information for
broadcast, runt, giant, and throttled packets. The last line (line 17) displays
any input, CRC, frame, overrun, ignored, or abort errors:
12439 packets input, 13257786 bytes, 0 no buffer
Received 202 broadcasts, 0 runts, 0 giants,
0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored,
0 abort
The output interface statistics begin with line 18 and end on line 21. This
data reflects the number of output packets, underruns, output errors,
collisions, interface resets, output buffer failures, swapped output buffers,
and carrier transitions:
12438 packets output, 13256434 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures,
0 output buffers swapped out
0 carrier transitions
Interface resets should be warning flags. If you see a large number of inter-
face resets after clearing the counter, you should be concerned. Interface
resets are caused by the following:
Queued packets not sent for several seconds
Hardware problems (for example, router interface, cable, or CSU/
DSU)
Mismatched clocking signals
Looped interface
Interface shut down
Line protocol down and the interface resetting periodically
The next warning flag should be carrier transitions. This counter counts
the number of times that the DCD (data carrier detect) signal changes state.
If the carrier keeps fluctuating, you do not have a stable circuit. This is often
a carrier problem, and the local carrier must be contacted.
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