Although you can use a router to segment the LAN, it is used primarily as a WAN device. Routers have LAN and WAN interfaces. In fact, routers communicate with each other through WAN connections. Routers are the backbone of the large internal networks and the Internet. It operates at Layer 3 of the OSI model, making decisions based on network addresses.
The two main functions of a router are the selection of the best route to and switching of frames to the corresponding interface. The router accomplishes this through the creation of routing tables and information sharing network of these tables with other routers. An administrator can maintain the routing tables by configuring static routes, but generally speaking, routing tables are maintained dynamically through the use of a routing protocol that exchanges information with other routers network topology (route). Read the rest of this entry »