Once again, stuck managing a Windows box. Yeah, I know, I’ll whine, bitch, moan, and cry you a river another time.
The Problem: Using the secondary NIC (PNET/VLAN), I found a lock of packet collision during negotiation, handshaking, and identification, causing Windows to give up and basically say, “well, since it’s not working, the cable must physically have been removed, because there’s no way I could ever be wrong.”
Wro…. err…. incorrect, Windows. (You’re wrong.)
The Discoveries: The truth was, at least in my case, that it wasn’t properly handling the gigabit capabilities of the card on the box. I’m not the administrator for these machines (though they’re housed in our datacenter), so I can’t be certain that nothing had changed recently, but their staff said nothing at all had been modified. Perhaps that really was the case, and nothing had been changed — Windows has been known to do stranger things than this, of course, sometimes out of the blue.
The Solution (for my case): Go to the screen where you can view your network adapters (your version of Windows dictates the path of navigation, hence the ambiguity). Next, right-click the adapter with the “Network Cable Unplugged” message and click “Properties.” Click the appropriate button to configure the network adapter. Then click the tab on that dialog for “Settings” or something of the like (sorry, but I logged out in a hurry, so this is from memory), and you’ll see a list of parameters on the left, with their values on the right. Find one related to speed and duplex, and if you see it set to “Auto” or similar, drop it to “100Mbps Full Duplex” and click OK. Close the properties dialog by clicking “OK” and see if the settings are already bringing the network adapter back online. If not, disable and re-enable the adapter, and – if it was indeed the same issue – you should be back online within a few seconds.