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New Member

Unreported errors on GigE fiber link?

For a long time, I’d felt that something was rotten with one of our remote gigabit links, but the interface on the 3350 didn't seem to indicate anything amiss; here are about 10 days’ stats:

3550#sho int gi0/8

GigabitEthernet0/8 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 0009.e8a0.7608 (bia 0009.e8a0.7608)

MTU 1504 bytes, BW 1000000 Kbit, DLY 10 usec,

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

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

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

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

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

Last input 00:00:00, 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 2000 bits/sec, 2 packets/sec

5 minute output rate 14000 bits/sec, 14 packets/sec

18055332 packets input, 3750142177 bytes, 0 no buffer

Received 303770 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 214840 multicast, 0 pause input

0 input packets with dribble condition detected

23846464 packets output, 4166981149 bytes, 0 underruns

0 output errors, 0 collisions, 1 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

3550#

This seems to say 3.7GB in, 4.2GB out, with no errors; similar “clean” stats were reported by the 3524 on the remote end. However, large files transferred from Outlook clients to an Exchange server were often "corrupted", (which IMHO is a cop-out word meaning something went wrong, but damned if we know what), and everything at the remote site seemed sluggish. Also, odd, random, telephone errors kept popping up.

The fiber cable connecting the remote building got badly kinked by a klutzy A/C mechanic a couple of years ago, so we've always wondered if it was OK, but the lights always blinked, and the switches at both ends reported no errors, so we didn't do anything about it. Working my way down the layers, however, I decided to check on it, and hooked up a gigabit cable analyzer, which puked big-time. The near end couldn't talk to the remote end at all, let alone run diagnostics.

So we replaced the cable, and everything seems hunky-dory. Exchange no longer reports corrupted files, the tester loves the link, and the switches continue to report no errors. People in the remote building think the network "has gotten faster". My question is obvious -- what kind(s) of error(s) would cause all these problems, but not be reported by the switches?

2 REPLIES
Gold

Re: Unreported errors on GigE fiber link?

you could be running into some dispersion type events caused by the bend in the fibre. the stuff is a bit touchy. think of it as wandering photons.

New Member

Re: Unreported errors on GigE fiber link?

I accept that there was in fact an error being caused by the bad cable. My question is, why wasn't this error being detected by the switch? It would seem that the error would have to ultimately cause some kind of CRC/FRC error, but no such errors were reported.

I like the "wandering photons" description. I'd put it in the same league with "bit rot".

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