FCS Error in 6504 Giga Fiber Connection

Unanswered Question
May 3rd, 2010

Hi All,

We have 6504 connected to the other end 3560G switch through 1000M LX SPF. I keep seeing the FCS and Runt errors in the giga port at 6504. The other end 3560G port is clean all the time. I changed the SPF module, still same issue. Changed the fiber from the patch panel to 6504. No help.

As I understand if I only see the receiving errors in 6504, that means only one fiber direction (3560G to 6504) has problem. Since 3560G doesn't have any receiving errors, it means the direction from 6504 to 3560G is clean.

I will try different patch panel port to see what will be changed. But is there any other troubleshooting I can take for this issue based on your experience?

Thanks a lot!

Lou

I have this problem too.
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Paolo Bevilacqua Mon, 05/03/2010 - 13:20

Do you have same SFP type on both side, and which type exactly ?

And which error ratio you have ?

hxmengmetro Mon, 05/03/2010 - 14:41

Both ends have same type SPF. 1000M LX SPF. We are having more than 10% receive errors at 6504 side.

Thanks.

Lou

Ganesh Hariharan Mon, 05/03/2010 - 22:35

Both ends have same type SPF. 1000M LX SPF. We are having more than 10% receive errors at 6504 side.

Thanks.

Lou

Hi Lou,

Genrally speaking if  you operate at full-duplex, errors in FCS, Cyclic Redundancy       Checks (CRC), alignment, and runt counters must be minimal. If the link       operates at full-duplex, the collision counter is not active. If the FCS, CRC,       alignment, or runt counters increment, check for a duplex mismatch in ports.

Check out the below link for troubleshooting error in interface/switch ports hope to help !!

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml

Hope to Help !!

Ganesh.H

Leo Laohoo Mon, 05/03/2010 - 15:13

Worst case scenario is to get someone who knows how to use an Optical TDR and run some test (including the patch cables).

hxmengmetro Tue, 05/04/2010 - 07:58

For this kind of FCS errors, what are the most possible reasons?

1. Bad patch panel ports.

2. Bad fiber slicing.

3. Bad patch fiber.

4. Bad SPF module.

I'm thinking sometime if the fiber slicing is bad or patch panel port is bad, the link could be totally down. Am I wrong?

Thanks.

Lou

Leo Laohoo Tue, 05/04/2010 - 15:43

Causes could either be:

1.  Dirty patch cable;
2.  Dirty SFP (yes, there have been cases of brand-new SFPs that are dirty);
3.  Incorrect SFP cables (best example is when your infrastructure cable is 60 micron but your patch cable is, say, 52.5 micron);
4.  Faulty SFP;
5.  Faulty switch/router appliance;
6.  Faulty termination of the fibre ports

Another example for #3 is when the fibre optics are terminated as "straight cut" but you are using "angle cut" (vice versa).

These are the factors that I could think of.

Make sure you have someone who knows how to use an Optical TDR (the latest Fluke tester is used as a "standard" here in Australia and specify "no null or unknown values" are allowed).

Hope this helps.

vvasisth Wed, 05/05/2010 - 02:03

CRC and Input errors  usually point towards layer 1 issues .

1)Please try using switchport nonegotiate  on both the sides

2) Hard code speed and duplex settings to 1000/full.

3)Enable  mdix auto on the 3750 and try using a 'straight through cable" 

3750stack(config)#int gig 1/0/3
3750stack(config-if)#mdix auto


4) If that does not helps disable mdix auto and try using a  different "cross-over cable'

5)Try using different ports on both the sides 

6)If incase we are using any GBICS can we try using a  different GBIC or SFP.
When operating at full-duplex, FCS, cyclic redundancy checks (CRC), alignment errors, and
runt counters should be minimal. If the link is operating at full-duplex, the collision
counter is not active. If the FCS, CRC, alignment, or runt counters are incrementing,
check for a duplex mismatch. Duplex mismatch is a situation in which the switch is
operating at full-duplex and the connected device is operating at half-duplex, or the
other way around. The result of a duplex mismatch is extremely slow performance,
intermittent connectivity, and loss of connection. Other possible causes of data link
errors at full-duplex are bad cables, a faulty switch port, or NIC software or hardware
issues.

Documentation:
http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech_note09186a008
015bfd6.shtml

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