Routers

Routers

A router is a connectivity device that operates at the OSI Network layer. The information available at the Network layer gives a router far more sophisticated packet-delivery capabilities than a bridge provides. As with a bridge, a router constructs a routing table, but the Network layer addressing information (discussed earlier in this chapter) enables routers to pass packets through a chain of other routers, or even choose the best route for a packet if several routes exist. (See Chapter 6 for more information on routers and how they operate.)

A hybrid device called a brouter combines some characteristics of a router and a bridge. A brouter routes routable protocols using information available at the Network layer and acts as a bridge for nonroutable protocols. (A routable protocol is a protocol that can pass through a router. TCP/IP and IPX/SPX are examples of routable protocols—see Chapter 5, “Transport Protocols,” for more information.)