FCS Errors

[Shepherd]

Hello, I've been reading this site for a few months now and I've found some really great information concerning Nortel devices.  My question isn't so much Nortel as my own inexperience hindering me.  I'm sure my issue will be a quick chuckle, but for the life of me I can't tell whether it's A or B.

We have two ERS 5530 switches, one in Building A, and another in building B.  We currently have a 1gbic in each switch, and it works well.  However, we were looking to upgrade from 1 to 10.  When we upgraded the gbic's, however, we started dropping packets and our users were unable to access network resources.  This is a single fiber line, no trunking.

When I performed a 'show port-statistics' I found that the switch in building B had roughly 1.5 million FCS Errors received &  they were stacking up rather fast.  It was a previously unused port on the switch, and the switch was new as I'd replaced it the week prior.

By my reasoning, it shouldn't be a duplex issue as they're both running 10Gbs / Full with Autonegotiation disabled.  If it were cabling then I would expect the 1gbic's to also have similar issues, if I'm not mistaken.   Without knowing any other steps to check/test or troubleshoot, I believe that it's an issue with the nic.  So, here's for my silly question:

If the nic in Building B is receiving the FCS errors then that would indicate a problem with the nic in Building A, correct?  I've never come across the issue before, so I'm hoping that I don't have things backwards - but my understanding is that since nic B is receiving the FCS Errors, then nic A is sending bad frames.

Is that correct, or am I completely wrong?

Thanks in advance for any assistance.  And thanks for this site.  It's been a great help.

[Michael McNamara]

Hi Shepherd and welcome to the forums!

You realize there are distance limitation to 1Gbps and 10Gbps depending on the type of fiber-optics used and they vary greatly!

You can start your research here;
http://blog.michaelfmcnamara.com/2009/05/10gbase-sr-and-fiber-cable-plants/

And here's a good review of all the different optics and their distances;
http://en.wikipedia.org/wiki/10_Gigabit_Ethernet

What SFP/GBIC are you using for your 10Gbps interface? What type of fiber-optic cabling are you using? (Multi-Mode or Single-Mode) You are most likely outside the spec for your optic (SFP/GBIC) and the fiber-optic cabling that you are using.

Good Luck!

[Shepherd]

Thank you, sir.  I'll have to check on the cabling, to tell you the truth.  Distance shouldn't be an issue as we're using single mode fiber with the XFP transceiver being 10GBase-LR.  The distance is less than a mile, so distance shouldn't be an issue.  What I did find out from the cabling crew was that it does terminate in two other points along the way, though.  So I'm going to have to pull out the module and plug it into a test switch I suppose.

From what I've seen, wouldn't FCS Errors appear on both ends if distance / poor terminations were an issue - not just appearing on one end like it is now?

[Michael McNamara]

There are two fiber strands that make up a fiber pair so you could have one dirty fiber strand where the symptoms would only appear on the Rx side of that strand.

You should probably have the cabling vendor test the fiber run.

[Shepherd]

Excellent point.  I had a feeling that I was missing something with this.

I'll have things checked as soon as possible then.  Thanks for the assistance!