Installers Expect a Single (Standalone) Machine
Most installers are highly qualified professionals who know the wiring you need for your broadband connection. It doesn't matter whether you decide on a cable connection, satellite, or DSLyou can depend on the installer doing a great job outside the house. The problem comes when the installer needs to connect the broadband to your machine. Many installers who work with DSL for a local telephone company or other organization handling home installations expect a single, standalone machine when they begin the installation. Mention a network and many of these installers are at a loss.
According to one story, an installer actually tried to connect a home network directly to the DSL line without an intervening router. Not only will this setup cause addressing problems with the internal network; it leaves the system open to attack. When working with a network, one machine will always have two network cards. The first card connects to the internal network and the other connects to the Internet. (For one of the systems, instead of a second card you can purchase external routers that include a built-in firewall and other features, but these devices normally cost extra.)
Even when you decide to use an external firewall, you should provide the added safety of a machine set aside for making the outside connectionone that you can easily configure and update as needed. Using several layers of protection is less expensive and more secure than one very expensive device that monitors all communications for the home user. However, the essential lesson, in this case, isn't that you need to provide two network cardsit's that you should know enough about your network before you order DSL that you can help the installers over hurdles (as strange as that might sound).