'Network cable unplugged' on one computer but not another

Question

We have hundreds of Dell OptiPlex 7050 computers here at work. I worked on a brand new one out of the box, configured it at my workstation as usual, and brought it out to the user's office. I plugged in the ethernet cable, but not able to connect, and it says "Network cable unplugged". I test the data jack with my network testing tool and the connection is active. I bring the computer back to my workstation and it works perfectly fine.

I work on another new computer out of the box, configure it at my workstation, and bring it to the user's office and it works fine. I can plug in the original computer at some different offices and it works normally, but some others, I get "Network cable unplugged" and I don't know why. We've had a few other computers (different models; one was an OptiPlex 9020) do the exact same thing and I just put them in a pile in my storage room until I can figure out what to do about it.

I tried upgrading the ethernet driver, rolling back the driver (if already updated), changing duplex settings, updating BIOS, rebooting, unplugging for a half hour and starting it back up again, etc. Is there anything else that I'm missing? If it was just a one-off, I probably wouldn't care as much - even though I had to do double-work because I had to prepare a 2nd machine that will actually work - but this has happened at least three times with three different computers at three different offices.

I've been working here for over 20 years and this problem has only happened the past year or so. Thanks in advance to anyone that can help me solve this mystery!

Rison

Tesla1856 · Answer

I'm a firm believer in ethernet wires for stationary machines (as apposed to WiFi) ... so I'll take a stab at this thread.

So, next time you have one that Windows complains about "Network cable unplugged" ... see if the port-light on the Ethernet Switch and the little LED on the NIC itself are off. If so, it could be a "cable problem".

Your ethernet tester ... does it check for actual signals or is it one of those little "2 piece sets" that just check that all 8 wires are connected and wired properly?

Since you also have 9020's doing it, doesn't sound like a problem with the 7050's. In that case, sounds more like a premise networking problem.

On long runs (or poor cables) I have seen Gigabit-capable machines try for a 1000 connection and then give-up (instead of falling back to 100). However, I don't think it says "Network cable unplugged" ... but it's been a while.

If you narrow it down to a premise networking problem (not computers) and the cables test fine ... take a close-look at your Ethernet Switches. When those go bad (usually only one-or-two ports at a time) the lights on both ends DO turn off and it says "Network cable unplugged". Basically, it acts like the wire is bad or disconnected. Those bad ports might do that intermittently and might start working after disconnecting/re-connecting cables. Resetting the power on the Switch might also temporarily fix it. But they are still bad and will fail again. Very hard to track-down. Just remember that Ethernet Switches do fail. I'm not a network admin and my experience is limited to un-managed switches.

Hope that helps or at least gives you some ideas.

RisonRG · Answer

Thank you, Tesla1856. Our network tool does check for an actual signal. It's not fancy or anything, but it gets the job done.

https://www.amazon.com/Smartronix-Linkcheck-Ethernet-Tester/dp/B000RGI6R6

The light on the NIC is off in the office where I get "Network Cable Unplugged" and on back on my workbench. I tested the data port with our ethernet tester and it says there's an active connection. I brought another computer there and was able to connect via ethernet, so that's why I'm so confused. I've had this same problem with different computers and locations a couple of other times, so I thought I'd throw it out there and see if anybody else has seen this and if there's a fix for it. We have a separate group at work that takes care of the network switches, but if they come out and test that everything is alright, since our ethernet tool and a different computer (same model) worked fine, I was hoping somebody has some magical tap-on-the-back-twice-and-sprinkle-sugar-on-top kind of confirmed wizadry that's escaping my brain at the moment.

Tesla1856 · Answer

That tester is handy, but not a full computer. It's really just a quick way to prove basic wiring and that the other end is connected to a switch's active port. I would not put much faith in it (as a 100% check) ... a real computer can do that (with full network link negotiation).

My suggestion would be to:

- In every office that has a problem, install a perfect, high-grade, tested, CAT-6 patch cable.Maybe use a new color if allowed.
- Keep a record of each office that fails and when
- Keep a record of each machine that fails and when

You will likely eventually see a pattern, and this chart should help the LAN technicians troubleshoot the network infrastructure.

Optiplex Desktops

"Network cable unplugged" on one computer but not another

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