Switch ports not working. - PC-side NIC lights steadily blinking on/off.

[tgrogan798]

I have my CCNA but unfortunately dont' have access to the switches I'm referring to, so I can't give more detailed information or look closer for the problem myself. The network admin says he doesn't see anything wrong and I know there is.

That being said, we replaced some switches a few weeks ago and afterward I keep having random machines losing connectivity. They are all 2960 model switches and all have had this problem.

The computers are various Dell models, with Broadcom and Intel nics. The front nic lights on the PC's are steadily blinking on and off, about .5-1 sec between. This is outside the OS, not a software issue.

Initially I just plugged them into a separate port on the switch to connect.  However, after more started randomly having this problem I spent more time troubleshooting. My goal was to identify one of the ports causing the problem since the drops weren't marked. However, I found in at least one case that it started working when I swapped connections to a different switch (which worked) and then when I plugged it back into the port that wasn't working it connected with no problems and has kept working for a few weeks now.

Does anyone happen to have come across this problem before or give me a clue as to what could be misconfigured?

[John Blakley]

Without knowing the topology and what the switches are seeing (logs, errors, etc.), everything would be just a guess. You could have loops in the topology, auto-negotiation may not be working correctly, cabling issues, etc.

[tgrogan798]

Auto-negotiation makes sense considering the way it's acting, although the network admin said it was set up correctly.

My first thought was cabling because a new lab prompted the new switches. But when it happened in area's that have worked for years now I ran a test on the cable all the way from the PC's patch cable to the end of the patch panel in the IDF and it was good.

Thanks for the suggestions. I just had the brilliant idea of manually switching a machine to full/half duplex in Windows to see what happens, something obvious I should have already tried.