|  | 2.2 | WANs and Routers
| 2.2.2 | The function of a router in a WAN
While routers can be used to segment LAN devices, their major use is as WAN devices. Routers have both LAN and WAN interfaces. In fact, WAN technologies are frequently used to connect routers. They communicate with each other by WAN connections, and make up autonomous systems and the backbone of the Internet. Since 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 (on the Internet, by using the Internet Protocol, or IP). The two main functions of routers are the selection of best paths for incoming data packets, and the switching of packets to the proper outgoing interface. Routers accomplish this by building routing tables and exchanging the network information contained within them with other routers. You can configure routing tables, but generally they are maintained dynamically by using a routing protocol that exchanges network topology (path) information with other routers. If, for example, you want any computer (x) to be able to communicate with any other computer (y) anywhere on earth, and with any other computer (z) anywhere in the moon-earth system, you must include 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 be able to communicate, or internetwork. However, any internetwork must also include the following: consistent end-to-end addressing addresses that represent network topologies best path selection dynamic routing switching
| Lab Activity
| In this lab you will examine a Cisco router to gather information about its physical characteristics and begin to relate Cisco router products to their function. You will determine the model number and features of a specific Cisco router including which interfaces are present and to which cabling and devices they are connected.