Help: Switch port with errors

Unanswered Question
Nov 6th, 2007

Yesterday a gigabyte port of 3750 catalyst switch was down suddenly, I did a shut and no shut and this port retrieve connection. Now, I am researching what happened and I can see in show interfaces output of this port the following:

Hardware is Gigabit Ethernet, address is 0014.69bc.0f9c (bia 0014.69bc.0f9c) MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:16, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

1780930 packets input, 257622708 bytes, 0 no buffer

Received 58460 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

163 input errors, 6 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 50188 multicast, 0 pause input

0 input packets with dribble condition detected

5486637 packets output, 606356394 bytes, 0 underruns

0 output errors, 0 collisions, 3 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

I can see 166 input error and I don't if it is important.

Anybody can help me to troubleshoot this port failure?.


I have this problem too.
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lgijssel Tue, 11/06/2007 - 00:32

This is a sinfle mode fiber link.

You should not see too much input errors there.

Possible causes:

input signal either too high or too low

faulty SFP (mostly on the TX-end)

damaged fiber patchcable



Kevin Dorrell Tue, 11/06/2007 - 00:32

I think this is an indication something is wrong. Personally, I start investigating if the error rate on a fiber link goes above a couple of parts per million. Normally I expect a fiber link to show zero errors.

I would start by replacing the GBIC of the equipment at the other end of this link. In my experience that is by far the most likely point of failure.

Kevin Dorrell


spremkumar Tue, 11/06/2007 - 00:53


can you check out for possible error logs with respect to this port ?

that might give some clue on what might have gone wrong or the reason behind the port going down...


mirtenmous Tue, 11/06/2007 - 01:54


I saw error logs with Cisco network assistant and this interface is the only one that have fcs errors (6 errors), also have few packet errors.

For other side:

This is the only way that I know to see logs erros. Is there another way?.


Kevin Dorrell Tue, 11/06/2007 - 02:02

If you do show int G2/1 counters errors, that will give you a better breakdown of the error types.

Kevin Dorrell


mirtenmous Tue, 11/06/2007 - 03:03


I can see 6 fcs-errors and 163 rcv-err in this command output.

I think it is very probable that it is a hardware error maybe gbic interface or fibber cable but I hdon't understand why port was donw suddenly. Is this a Cisco switch procedure when an errors ocurred in any port?.

I didn't remember say that in the other side of switch there is a media converter that converts fibber to copper. THe fibber is multimode.

Kevin Dorrell Tue, 11/06/2007 - 03:36

So you have a total of 163 errors, of which 6 are CRCs. Did it not give any indication what the other 157 are?

Kevin Dorrell


spremkumar Tue, 11/06/2007 - 03:05


you can check the same using show logs from your console or telent session.


mirtenmous Tue, 11/06/2007 - 03:11

I can see nothing about this interface or something relevant with this command


MZydorczyk2 Thu, 11/08/2007 - 12:49

I am having the same problem with one of our switches. What would be a possible problem if a majority of the input errors were CRC errors?


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