My company uses a commercial software product that employs a NIC's MAC address as part of its security dongle. We've used this product on Dell and Compaq laptops running Windows NT, and the software works both when the laptops are connected to the network (through a 3Com PC Card) and when the users are roaming.

We're beginning to use new laptops with Windows 2000 preinstalled. We want to migrate our mobile users from the NT laptops to the Win2K laptops, but we're having trouble with the software I described. As soon as a migrated user starts a Win2K laptop without a network connection, the dongle fails. Apparently, the software can't find the MAC address because the OS has switched off the PC Card. The software will work only when the laptop is connected to the network through an RJ-45 cable connected to an active port.

The computer vendor tells us that our problem involves the OS and that we need to talk with Microsoft. Microsoft tells us that the problematic OS behavior is "a feature and by design." The software vendor doesn't know a way around the problem. Do you know a registry fix or some other method that we can use to fool Win2K into keeping the PC Card active regardless of network connection?

Win2K's Media Sense feature, which the OS uses only in conjunction with TCP/IP, detects a Win2K system's NIC connection to a network. When the system is disconnected from the network, the OS removes all bindings from the adapter. To turn off Media Sense, open a registry editor and go to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters subkey. Add the registry value DisableDHCPMediaSense (of type REG_DWORD) and set the value to 1.

This fix is best used only on laptops. (The Microsoft article "How to Disable Media Sense for TCP/IP in Windows 2000" at http://support.microsoft.com/support/kb/articles/q239/9/24.asp describes the feature and the registry fix.)