Router LANs and WANs

Routers can be used to segment LANs, but they are mainly used as WAN devices. This page will explain how routers are used in a network.

Routers have both LAN and WAN interfaces. WAN technologies are frequently used to connect routers. Routers use WAN connections to communicate with each other.
Routers are the backbone devices of large intranets and of the Internet. They operate at Layer 3 of the OSI model, making decisions based on network addresses. The two main functions of a router are the selection of best path and the switching of packets to the proper interface. To accomplish this, routers build routing tables and exchange network information with other routers.
An administrator can configure static routes to maintain routing tables. However, most routing tables are maintained dynamically through the use of a routing protocol that exchanges network topology information with other routers.
For example, if Computer X needs to communicate with Computer Y and Computer Z in Figure
, this requires a routing feature for information flow and redundant paths for reliability. Many network design decisions and technologies can be traced to this desire for Computers X, Y, and Z to communicate.
A correctly configured internetwork provides the following:

Consistent end-to-end addressing

Addresses that represent network topologies

Best path selection

Dynamic or static routing