input error questions

Unanswered Question
Feb 12th, 2009

My situation is as follows. We are connecting from a 4510R (Sup V), WS-X4418-GB blade to a 3750G-48PS-E. The distance is around 1500 feet (MM fiber), patching fiber through one other location. When I use a WS-G5486 GBIC and GLC-LH-SM SFP with mode conditioning cables at each end, I see the numerous input errors (runts and CRCs).

GigabitEthernet1/7 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet Port, address is 0021.555b.a73f (bia 0021.555b.a73f)

Description: to IDF07 SCAX009A01G; G1/0/50

Internet address is

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 241/255, 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 1000BaseLH

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

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

Last input 00:00:02, output never, 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

L3 in Switched: ucast: 5573 pkt, 416844 bytes - mcast: 0 pkt, 0 bytes

L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes

41492 packets input, 8972491 bytes, 0 no buffer

Received 35742 broadcasts (29759 IP multicasts)

7042 runts, 0 giants, 0 throttles

25996 input errors, 18954 CRC, 0 frame, 0 overrun, 0 ignored

0 input packets with dribble condition detected

57006 packets output, 9372991 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out

When I connect this same 1500 foot link using a WS-G5484 GBIC and a GLC-SX-MM, I see no errors at all.

In other words, using MM throughout even though the distance is a bit out of spec, I see no errors. When I try to operate within spec and use mode conditioning cables with a single mode GBIC and SFP, I take errors.

If this were my only link, I would just run it out of spec (because it's not that far out). My overarching issue is that I have ten connections of long length, some up to 3000 ft through multiple other locations. I think that it's unlikely that running MM throughout all these connections will be successful.

Has anyone seen anything like this before? It almost seems as though the problem is isolated to the blade on the 4510. Perhaps I got a bad batch of GBICs and/or SFPs? Or bad mode conditioning cables?

Thanks for any thoughts.

I have this problem too.
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b.julin Thu, 02/12/2009 - 18:33

How old is the fiber?

Is it some of that larger diameter stuff -- maybe the aperture on the mode cables is not working right? I know they sell different ones for different diameters.

Have you tried just by putting a plain old single mode patch on the TX side rather than the fancy offset cable? Sometimes that can work.

dsmcneil Thu, 02/12/2009 - 20:32

The fiber is likely around 5 years old or so, 62.5. Unfortunately, we don't have any single mode cable...would that work with multimode in the middle (for the large majority of the fiber run)?

Thanks for the insights.

b.julin Fri, 02/13/2009 - 10:41

I run a few links that have 2 or 3 segments of multimode plant fiber, patched in the middle with multimode, with LH transponders attached at either end with a cable made out of two halves of a standard multimode and a singlemode patch. Not quite sure how long the runs were but they were too long for MM SX.

We bought a small inline coupler meant for mode buildout just in case it started to act up, more for CYA purposes than anything else. We haven't had a need to use it.

Mohamad Qayoom Fri, 02/13/2009 - 12:10

Please ensure that you are connecting the mode conditioning cables correctly. If you plug in the RX and TX ends incorrectly, you will see a lot of errors.


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