CRC Errors on Network

[jamesch]

I have a question? We recently relocated to a new building, and had new CAT5e cabling installed into a certified CAT5e patch panel, about 50 connections total. The network Runs Windows 2000 server and a mix of Windows 2000 pro, and NT4.0 workstation. I recently ran Network monitor on the server and noticed that is was logging lots of CRC errors under the hardware portion. The research I have done show that this could be either a cabling problem or a bad NIC. I did isolate in network monitor to monitor to just on computer, and ran a test, it logged CRC errors left and right, then took that computer in the server room and setup a temp workstation with that computer, and plugged straight into the switch, ran Network monitor again and no CRC errors were logged. Does this mean that the cable in the users room is bad? I told the Cable guys and they said they tested the cabling with a Fluke DSP-4000, and the test passed. Will we also have a Fluke DSP-4100, with current software, ran the test and it passed also. I have found that NEXT tests are what to look for, but what standards do I use to determine the bad from good, and how to stop CRC errors??? HELP

 

[svermill]

I realize this isn't exactly the answer you're looking for, but I would do a quick check to see if a different machine/NIC can pass traffic over that particular cable before I went any further.

 

[daronwilson]

I think that you are doing the right thing, basic troubleshooting. Involved in the circuit are the PC, the NIC, the patch cable, the horizontal cable run (already tested ok, twice), the patch cable, the switch port. You've pretty much ruled out the horizontal cable, though it wasnt clear whether you tested for channel or link, so you may or may not have ruled out the patch cables at each end. So, what order you swap things around really doesnt matter. I've found that you always discover the problem in the last place you look (obviously because you quite looking at that point . So, try a different PC on the same patchcord/wall outlet/patchcord/switch port. Then swap switch ports, then replace the patch cord, then replace the other patch cord, etc.

One suggestion, if you really what to know where the problem is, only replace/change ONE item then retest, and always retest with the same test. I suspect you will find a bad patchcable at the workstation end or a bad NIC.

As for NEXT and all the other measurements involved in the test, the test instrument has a table built in that checks all those levels at all the frequencies you tell it for Category5e compliance. If your wire run passes the test, there is really little to be gained by getting into the various NEXT, FEXT, etc. My Wirescope 350 prints nice graphs when it is done, showing the required standard levels for various frequencies, then showing exactly how this cable compared. With that, you can see where the worst case figure was. But, so what. What difference would it make to me if I knew that I passed the NEXT test, and that I passed it by a 5 dB margin at 60 MHz? I don't see anything I would be alerted to do to the horizontal cabling system to try to lower the NEXT specifically at 60 Mhz, so it really isn't much of a diagnostic tool.

SO, assuming you brought the workstation into the server room, plugged it into the same switch port as the horizontal cable run was plugged into, and it runs with no errors, it may not be the NIC. However, the NIC tranciever could be weak too and could do fine at a short distance. I guess I would take the PC to another cabled location and test it on a similar length of cable. Just need to check one thing at a time and determine where the breakdown is.

Good Luck! It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[jamesch]

Thanks, for the advice Daron. The tests were with channel adapters plugged into the patch panel and the wall outlet, and we have not tested the patch cables at both ends, that was my next step. We have three floors in the building and the 2&3 floors are under reconstruction, and we plan to occupy the floors. Currently the cable guys are wiring those floors. If they were doing something out of the ordinary, and we had problems on the 1 floor, I wanted to make sure the 2&3 floors were going to be done properly. I read another guys article about the little gremlins on a LAN, and one of the biggest things that LAN Admins don’t look at is CRC error, and getting lots of them on a LAN is bad, so he says! Will take your advice and test the patch cables at both ends, and move the PC to a different office, one that didn’t show any CRC errors on the monitor tests.

 

[ZachBenj]

Make sure your ports on the switch match the setting that the NIC has. AutoNegotiate is not a science it is an art. My suggestions are what I would try myself. If incorrect, I welcome corrections to my knowledge.
Scott
stomlin@baptistfirst.org