LANs, generally speaking, are collections of interconnected nodes, all of which are geographically nearby, such as in the same room or in the same building. A node is any device which can be networked, like a computer (often referred to as a system), a printer, an appliance (web server, NFS server, etc.), or a black-box device (usually a router or switch_we define these later in this chapter). It should be noted that with the advent of layer 2 routing (see Chapter 16 for a discussion of layer 2 routing or switching; layers are discussed in the next section), the notion that the nodes within a LAN must be geographically close becomes untrue.

A WAN is a collection of interconnected and geographically disparate nodes. Often, the major distinction between a LAN and a WAN is the use of some form of high-speed media to interconnect the nodes. Such media includes microwave, satellite, and telecommunications connections. WAN is a very general term that is often applied to collections of LANs and other WANs as well as collections of nodes. One example is the Internet, which is frequently described as a WAN_in fact, the Internet interconnects both LANs and WANs.

The term CAN is usually applied to LANs or WANs that comprise the collection of interconnected nodes belonging to a single company or university/college but whose interconnection extends across many buildings.

This term is usually applied to the collection of nodes within a metropolitan area that fall under the same corporate control such as that of a telecommunications company or independent service provider (ISP).