The Open Source Journal

In this post, I explain how I solved the mysterious "Cable is unplugged"-even-though-it's-not,-REALLY problem. The solution is simple and the problem is so very, very annoying. Read on to find out how I troubleshot and solved my nForce5 onboard Ethernet breakage (M2N-Sli Deluxe motherboard).

Six months or so ago I purchased my current machine, on the Asus A8N-SLi Deluxe motherboard. One of the reasons I chose this board was because of the dual gigabit ethernet adapters. A couple of weeks ago I also decided to give Microsoft Vista x64 Ultimate a try.

After installing my standard array of Windows applications (Trillian, Half-Life 2, Office 2007, etc...) I began installing VMWare. Since I typically do a fair amount of work in virtual machines, including moving large amounts of data, I like to use one NIC for "Windows" traffic and the other for VMWare traffic. So I plug them both into my gigabit switch and unbind services appropriately:

My Windows Vista Network Adapter Properties and Bindings

You might have guessed that I use bridged networking in VMWare and not NAT...typically my VM's run services and often times have static, publicly accessible IP addresses.

The Problem

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After turning on my computer and firing up VMWare today, I received a warning that the virtual network would be down due to my physical network interface being disabled. A quick glance at my router confirmed it - I was missing a blinking LED.

Checking the network settings, I found out my problem: "Network Cable Unplugged." Clearly a cable had come loose; I notice the LED lights on the back of my computer are off, confirming the cable problem, so I quickly unplug and replug the cable. Nothing, not a single light.

Troubleshooting

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So I begin a more in depth solution - I change cables a couple of times, try different ports, try disabling and re-enabling the network interfaces in Windows, rebooting the switch, and finally uninstalling the network devices altogether and rebooting the machine to make sure they were both enabled in the BIOS (which they were).

I reboot back into Windows, hoping that Windows will fix itself when it reinstalls the devices. No such luck: the first nVidia nForce Networking Controller still reports itself as "Network Cable Unplugged." Perplexed, my search begins: I hit Google, looking for 'nvidia nforce ethernet "network cable unplugged"'.

After going through the first dozen or so results, most of which suggest people to do things I've already done, I find a couple that talk about forcing the network controllers into 100 megabit full duplex mode and/or disabling offload settings. I try these to no avail.

Stumped and losing hope, I turn off my computer again. Again I swap out the cable, this time with a brand new Cat 6 cable, and then a Cat5 cable that came with an old Linksys router. Nothing.

Success!

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So I'm sitting in my chair, asking why one light is lit while the machine is off. Obviously it's in a low power state, waiting for a magic packet to wake the machine. On a hunch, I flick off the power on the back of my power supply and watch the switches green light die. Another flick of the power supply, and what do I see? Both LEDs light up!

I'm still not quite sure what the cause of the problem was; the other day I had rewired some of my cables when installing a Kill-A-Watt from ThinkGeek. Perhaps it was a quirk of cabling and power. But clearly, it was not a problem with Windows Vista, or the nVidia drivers themselves. So if you ever have problems with your nForce-based motherboard (mine is a nForce 5 570 Ultra AMD, in case you're curious) saying a network cable is unplugged and you're damn sure it's not, I suggest you power off your machine and unplug / switch off your PSU. This simple solution certainly solved my problems.

-Vlad