"You can think of a wireless router as the center of a single LAN. Every device connected to a single router—whether connected physically by Ethernet cable or wirelessly—is part of the same LAN.
"Now suppose you have a device that is not part of the LAN, but you want it to be. The problem is that you don’t have an easy way to connect it. For example, you might have a printer or a gaming console, such as the Xbox or Wii, which only has a cabled Ethernet connection. If the device is far away or on another floor from your wireless router, running a cable could be complicated.
"The solution is a wireless bridge. Using a second wireless router installed with DD-WRT, the router will connect to your primary router and share the network with any connected Ethernet devices (most routers have four built-in Ethernet ports, but you can add one or more external switches with four, eight, or more ports each to expand even further)."
