Multiple LAN Connections

Most desktop computers sit where they are installed, gathering dust until they're obsolete, and participate in only one LAN. But portable computer users often carry their computers from office to office, docking or plugging into several different local LANs. While Microsoft has made it easy for you to manage several different dial-up and VPN connections, it's difficult to manage connections to several different LANs if the network configuration settings are manually set.

Internet Protocol settings are the difficult ones. If your computer is set to use automatic TCP/IP configuration, you won't encounter any problems; your computer will absorb the local information each time you connect.

If your TCP/IP settings are set manually, things aren't so simple. Microsoft has come up with a partial solution called Alternate Configuration. You can configure your computer for automatic IP address assignment on most networks, and manual assignment on one. The way this works is that Windows looks for a DHCP server when it boots up, and if it doesn't find one it uses the Alternate Configuration. This can be a static IP address, or the default setting of Automatic Private IP address assignment, whereby Windows chooses a random address in the 169.254 subnet. (The automatic technique was the only option in Windows 98, Me, 2000 and XP.)

This means that your computer can automatically adjust itself to multiple networks, at most one of which requires manual IP address settings.

To set up Alternate Configuration, open Network Connections, view Local Area Connection's properties, and double-click Internet Protocol. Be sure the General tab uses the Obtain an IP Address Automatically setting. View the Alternate Configuration tab and choose User Configured to enter the static LAN's information.

If you need to commute between multiple networks that require manual configuration, you'll have to change the General settings each time you connect to a different network. I suggest that you stick a 3-by-5-inch card with the settings for each network in your laptop carrying case for handy reference.

NOTE

Although it appears that Microsoft isn't going to solve this problem for us, we can hope that third-party software developers will come up with a tool to manage multiple LAN connections properly. Back on Windows 95 I used a program called Network Hopper that let you choose from a list of multiple network setups. It changed not only the IP address info but even email setups, so that the appropriate mail servers were used on each network. A tool like that for Windows XP would be a real blessing. Attention developers: Care to take this on?