Network cable keep connecting/disconnecting rapidly or so does Windows tell me.

Hi,

Suddenly this morning one of the computer on our network keeps dropping it's network connection. The computer run an up to date Windows XP Pro and is a Lenovo 3000 J110 computer. The network card is onboard and "from" Broadcom.

As soon as the computer is started Windows report that "A network cable is unplugged". Soon after, the cable seem to be plugged in again and windows report "Acquiring network address". It then proceed to go from the first message to the second every 5-20 seconds.

If I look behind the computer the LEDs near the network plug are not lit when the computer report that the network cable in unplugged.

• I've tried a new cable, same problem.
• I've tried another computer on this cable, worked fine.
• I've tried downloading and reinstalling the network adapter drivers, same problem afterward.
• I even tried disconnecting the power from the computer for a minute, did not solve the problem.

Does anyone have any idea what might be the problem. Otherwise, what should be my next step in diagnosing this problem?

From serverfault Mathieu Pagé

• You didn't mention what happened with the other computer using that cable.

  The other thing could be a problem with the switch/hub port. Try restarting the switch, if that doesn't work, change the port it's jacked into.

  Mathieu Pagé : The other computer worked fine when plugged in this cable. I'll try to reboot the switch anyway, just in case.

  Bart Silverstrim : What kind of switch is it? I've had SOHO router/switches start to go flaky, the ones that cost <$100. Typically last a year or two, then go nuts with the switching, the wireless function, etc. and the best solution was to chuck it. No rhyme or reason to it, they just up and died one day.

  Mathieu Pagé : This computer and another one are connected into a cheap (definitely less than $100) 5 ports switch so they can share one wall outlet. I restarted this switch and the problem got away. Because the other computer was working correctly on the said switch I supposed it was working fine. Wrong assumption. Thanks for the help.

  Bart Silverstrim : I've had that happen too. One port will act wonky but other systems act fine. Doesn't make much logical sense at first but a restart can clear up whatever in the firmware is going nutters.

  jer.salamon : sounds like my office multiple computers plugged into 1 wall jack :(

  Bart Silverstrim : @Xjerx-you mean you have multiple computers going into one drop that then goes back to a low-end switch in the closet? I wouldn't be surprised if that can cause issues once in awhile with the routing of packets, or performance issues at the least.
  From Bart Silverstrim

• I'd echo Bart's statements re: trying another port on the switch, etc.

  You don't mention if this has ever worked before. I've seen this behavior with old, early 10/100 Ethernet switches (late 90's 3Coms come to mind) when the autonegotiation doesn't work properly. If this hasn't ever worked before I'd investigate if the switch is properly configured for autonegotiation and, if not, I'd try "hard setting" the port to a speed and duplex (reluctantly, mind you).

  Edit:

  Since it's been working for awhile I'd recommend looking at the switch's logs (if it has any) and, failing any error messages there, I'd consider rebooting the switch. Most switches don't have any ability to maintain persistent logs across boots and, since you really want to find a root cause (you do, don't you?), you should look at the log before you reboot it.

  Trying a known-working device in the port that's acting flaky might tell you if it's the port, as well. You could do that before you reboot the switch (if you get to that point).

  Scott Lundberg : Beat me by 1 min. :-)

  Mathieu Pagé : Yes, it worked for years litteraly.

  Evan Anderson : @Mathieu: I've dropped on an edit with some addt'l suggestions.

  Mathieu Pagé : @Evan: Thanks I resolved the problem by restarting the cheap switch that was between the computer and the main office switch.

  Evan Anderson : @Mathieu: Good to hear. Cheapie Ethernet switches have been the cause of more problems in my experience than you'd probably guess. They definitely can fail in strange ways (some ports working, others failng) like you saw today. I'd keep an eye on the switch because, in my experience, a partial failure like you saw today often preceeds a complete failure.

  Bart Silverstrim : Cheapie switches are good for home, and that's about it. I know they're often marketed for SOHO use, but unless your office has five systems going through it, make the jump to a decent managed switch...SOHO switches are good for home just because they're simple enough for a couple systems to use and when they die you can buy another one as backup to switch them out. But if I relied on them to make money (in a business) no way! :-)
  From Evan Anderson

• We had a similar problem with a broadcom card and an incompatibility with the switch. Did you have an update to the driver that may have started this? In any case, the solution for us was to hard code the link speed and duplex. Try 1Gb/full duplex and work your way down from there.

  Mathieu Pagé : Nothing changed recently, except maybe automatiques Windows updates.

  Mathieu Pagé : Oh, and it used to work until this morning.

  Bart Silverstrim : Check the Windows Update log to see when/if driver updates came through.
  From Scott Lundberg