Started having a problem with the generic error message “network cable unplugged” on several virtual machine guest OSs, running on Microsoft’s Virtual Server 2005 R2.  The problem happens infrequently, however, it is difficult to catch without cross-monitoring (one VM monitoring another VM for network connectivity). 

I don’t know why the problem is happening.  A search on Google (web, groups, etc.) does indicate that others have experienced the problem, but there are no solutions that I can find.

My workaround is to simply restart the NIC when connectivity is lost.  To do this, I am using Microsoft’s “Devcon” tool: http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q311272.  Download and unzip the tool to a working directory.  I have a tools directory in place, so I unzipped the files in a subfolder named “devcon”.  Complete path: c:\tools\devcon.  When unzipped, two sub-directories are created, “i386″ and “ia64″.  Most will use devcon.exe in the i386 folder.

To use the tool, you have to first identify the name of your NIC: Right-click on the LAN icon in your task-tray, select “Open Network Connections”, then look for your NIC.  You are looking for the hardware name of the device.  This could be “Broadcom…”, “Netgear…” etc., that will be used to search the list of devices supplied by devcon.  First, create a list of all devices:

devcon.exe findall * > list.txt

The list will contain all of the devices on the machine and their respective descriptions.  Next, open the file “list.txt” in notepad and find (Ctrl+F) your NIC device, for example search for “Broadcom”, or “Netgear”, or one word that describes yoru NIC.  In my case, the device name, the text preceding the description and colon is:

PCI\VEN_14E4&DEV_170C&SUBSYS_01D81028&REV_02\4&2FE911E8&0&00F0

This device name will then be used to disable and enable the NIC from the command line using devcon:

devcon disable PCI\VEN_14E4&DEV_170C&SUBSYS_01D81028&REV_02\4&2FE911E8&0&00F0

devcon enable PCI\VEN_14E4&DEV_170C&SUBSYS_01D81028&REV_02\4&2FE911E8&0&00F0

It’s as simple as that. 

Now, when my network connection goes down, I first assume that there is a problem with the network connection, and restart it.  It’s not a perfect solution, but it will at least prevent some downtime.