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Why does ethernet adapter keep saying network cable unplugged?

Posted on 2014-01-03
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Last Modified: 2014-01-23
Hello experts,

I am pulling my hair out at this point.  I can't for the life of me figure out why this is happening... We have a couple of computers that keep telling me that the ethernet cable is unplugged or is broken.  I've replaced the cable both going from the wall to the computer and also from the patch panel to the switch, to no avail.  I've used a toner and probe and I can read the tone perfectly without a problem.  It is patched to the correct patch panel port and everything is good.  I don't see lights on the NIC part of the laptop where the cable goes in, but I don't know if the laptop has lights, I don't think it does.  On the switch, all the lights come on like they should.  I also have tried using a different switch and it still doesn't work. Why do you think this keeps happening?  I can't figure out what could be causing the NIC to be not responding when plugged in with a cable.
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Question by:Brent Johnson
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by:Nick Rhode
ID: 39754961
Was this Jack working before?  If you plug the laptop directly into the switch does it work?  Would need a cable tester for the wall, something that would test the pins for a line might be crossed or not punched properly which relates to my 1st question.
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by:Gareth Gudger
ID: 39754982
Does the laptop work at a known working jack?

Does a known working laptop work at the problem jack?
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by:lruiz52
ID: 39754992
To add to what nick said, have you checked the bios on the laptop and verified that the built in Ethernet is enabled.  Also check the driver.
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Author Comment

by:Brent Johnson
ID: 39755032
I still have no clue what happened, but now it's working.  It does that frequently though and I don't know why.  All I did just now was plug a different laptop into that faulty jack and it worked fine on the other laptop.  Then I plugged the cable back into the computer that belongs there, and by some miracle, it worked.  Why does this weird thing keep happening?
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by:ChiefIT
ID: 39755181
It could be a number of reasons:

let's start with a a couple question.

Is this intermittent (meaning you don't change ports, but the nic red X's out periodically)?

..Or does it X out on specific ports?..
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by:akahan
akahan earned 166 total points
ID: 39755353
"Network cable is unplugged" doesn't mean the network cable is unplugged.  It's a very unhelpful message.  What it means is that the operating system can't tell that you're connected to anything.   This usually has nothing to do with cabling, and everything to do with configuration.

The intermittent nature of your problem suggests that it's either power being sometimes turned off to the network card, or an intermittent failure to negotiate a connection.

Check the network card's properties in the laptop.  Make sure that in the Power settings for the network card, you don't have "Allow the computer to turn off this device to save power" selected.

Also check and make sure that the network card isn't set to Auto Select speed and duplex in the Advanced tab of the network adapter properties dialog box. If it is, try changing it to a specific bandwidth (10 or 100 or 1000, whichever is appropriate for your network).
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by:Darr247
ID: 39755540
Try disabling the wireless adapter and see if the NIC keeps giving you that message.

I never saw a specific OS mentioned, so it's about impossible to give specific instructions on how to disable the wireless adapter.
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by:Gareth Gudger
ID: 39755562
See if the NIC has any power save options. Some power profiles will disable the NIC if they are on battery.
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by:masnrock
ID: 39755765
If it's intermittent, then it might be an issue involving autonegotiating speed with the switch. But also make sure the BIOS and NIC drivers are up to date. You could also try making sure the firmware of the switch itself is up to date, or even testing using a different switch.
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by:Craig Beck
ID: 39757638
Have you tested the cabling with a proper cable tester, instead of just toning it?  It may be that one of the orange or green wires in either pair is broken or intermittent somewhere between the outlet and the panel.  That would give the effect that on the switch the port is up, but at the NIC it looks down.

What switch do you have?  Maybe you can do a TDR test from it?
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Author Comment

by:Brent Johnson
ID: 39759973
Thanks for all of your answers everyone.  To answer a few people back....

ChiefIT - I'm not sure what you mean when you ask if it red x's out on specific ports... Like actual wall jacks?.... But what I can tell you is that the little computer ethernet icon next to the clock red x's periodically.

Darr247 - I tried disabling the wireless adapter.  Still gave me the red x.

Craigbeck - We have two switches.  One of them is a Rosewill RGS-1024 and the other is Cisco SLM2024.  It doesn't matter which switch that port is patched into... it keeps giving red x's periodically.  

No, I haven't ran a cable check with a tester yet because I don't have one.  I recently ordered one and I'm waiting for it to ship to me.

The laptops are all running Windows 7 Pro.
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by:ChiefIT
ID: 39760130
"computer ethernet icon next to the clock red x's periodically"

-Intermittent, so it's not a solid red-x?

-Assuming you are using the same switch port and wiring.

This still could be a couple issues.
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The most likely is a duplex mismatch: There is a quirk with cisco routers and switch equipment. The duplex settings have to exactly match the other routers and switches. You can not configure switch to switch or switch to router ports differently. (I say cisco, because it's the only manufacturer I have seen this on).

As an example: Your router to switch ports can not be configured as 1000Mb/Full duplex on the router, while the Cisco switch is configured Auto negotiate the duplex settings. Another example: your Rosewill Switch can not be configured 1000Mb/full duplex while the Cisco is configured to Auto negotiate.
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It still could be other issues, but the duplex mismatch is something I have seen most commonly causing this problem.
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by:masnrock
ID: 39760335
Try setting your NIC and its respective switch port to 100 mbps. If the drops end, them it was indeed a negotiation issue. HP can be dumb in this regard too sometimes.
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by:Craig Beck
ID: 39760357
If it is a negotiation issue, that usually points back to cabling.
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by:ChiefIT
ChiefIT earned 167 total points
ID: 39760606
I agree this is most likely a duplex mismatch of some sort (whether physical wiring or configuration of the switches/router).

Craig: I always had a network analyzer to test ports, myself so I knew if cabling was right or not before going further. If a cabling issue, which would physically mess up duplex, would it be intermittent or consistent knock down of the port?

Masnorock: If an HP switch would the entire switch be affected, or just the ports that are mismatched?

From my personal experiences:
My cisco router mismatched my cisco core switch. Computers were going up and down on the network, and it was intermittent which computer went down. They would go down individually for about 5 minutes come back up for about 5-10 minutes. So, I know this author's feeling when it was unexplainable.  The router was a 1Gig router port and the configured to auto negotiate. The switch was a gig port hard configured to 1000mb/full duplex. Neither were wrong, but the difference in hard coding and auto negotiating duplex messed up Cisco. I found out it's just a Cisco quirk, but learning this problem can come also from HP equipment.
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Craig Beck earned 167 total points
ID: 39760647
@Chief - it could be intermittent if it's a noise issue or poor termination rather than a physical break.  If there are periods of noise then no noise (electrical interference from the mains supply for example) you might have just tested when the load on the mains was low.  If it was a physical break though it would probably not be intermittent as the same error condition would be true permanently, unless it was a cable which moves slightly from time to time maybe.

Cisco implemented a different version of auto-negotiation back when it was uncommon for all devices to support it.  They recommended to manually set the speed and duplex to be sure you had the parameters correct.  Even when it became the norm Cisco still used their own implementation though (as they do with everything), but nowadays it's the same as everyone else so it's less of an issue.

You can get issues with autonegotiation if one end is set manually and the other end isn't able to work out what it's using.  Sometimes though it works without a problem - I think it's just hit-and-miss really.  A lot of kit will check the speed first then decide what duplex setting to use.  If it's FastEthernet (100Mbps) it will go to full-duplex, yet if it's Ethernet (10Mbps) you'll usually see a half-duplex link.  This will be the default (10/half) if autonegotiation at each end fails.  The GigabitEthernet standard requires autonegotiation, so you shouldn't manually set speed and duplex for 1000Mbps transmission.  If a GigabitEthernet link fails to negotiate the first place I look is cabling - always.

It's always hard to predict though, which is why it's usually a cabling issue :-(
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