System information

Troubleshooting Serial Line Problems 15-341
show interfaces serial
output hang Number of hours, minutes, and seconds (or never) since the interface was last
reset because of a transmission that took too long. When the number of hours in
any of the last fields exceeds 24, the number of days and hours is printed. If that
field overflows, asterisks are printed.
Output queue, drops
input queue, drops
Number of packets in output and input queues. Each number is followed by a
slash, the maximum size of the queue, and the number of packets because the
queue is full.
5 minute input rate
5 minute output rate
Average number of bits and packets transmitted per second in the past five
minutes.
The five-minute input and output rates should be used only as an approximation
of traffic per second during a given five-minute period. These rates are
exponentially weighted averages with a time constant of five minutes. A period of
four time constants must pass before the average will be within 2% of the
instantaneous rate of a uniform stream of traffic over that period.
packets input Total number of error-free packets received by the system.
bytes Total number of bytes, including data and MAC encapsulation, in the error-free
packets received by the system.
no buffer Number of received packets discarded because there was no buffer space in the
main system. Compare with ignored count. Broadcast storms on Ethernet
networks and bursts of noise on serial lines are often responsible for no input
buffer events.
Received...broadcasts Total number of broadcast or multicast packets received by the interface.
runts Number of packets that are discarded because they are smaller than the medium’s
minimum packet size.
giants Number of packets that are discarded because they exceed the medium’s
maximum packet size.
input errors Total number of no buffer, runts, giants, CRCs, frame, overrun, ignored, and abort
counts. Other input-related errors can also increment the count, so this sum might
not balance with the other counts.
CRC Cyclic redundancy check generated by the originating station or far-end device
does not match the checksum calculated from the data received. On a serial link,
CRCs usually indicate noise, gain hits, or other transmission problems on the data
link.
frame Number of packets received incorrectly having a CRC error and a noninteger
number of octets. On a serial line, this is usually the result of noise or other
transmission problems.
overrun Number of times the serial receiver hardware was unable to hand received data to
a hardware buffer because the input rate exceeded the receiver’s ability to handle
the data.
ignored Number of received packets ignored by the interface because the interface
hardware ran low on internal buffers. Broadcast storms and bursts of noise can
cause the ignored count to be increased.
abort Illegal sequence of one bits on a serial interface. This usually indicates a clocking
problem between the serial interface and the data link equipment.
carrier transitions Number of times the carrier detect signal of a serial interface has changed state.
For example, if data carrier detect (DCD) goes down and comes up, the carrier
transition counter will increment two times. Indicates modem or line problems if
the carrier detect line is changing state often.
packets output Total number of messages transmitted by the system.