There are a number of terms used to describe different types of networks. Such terms include local area network (LAN), wide area network (WAN), campus area network (CAN), and metropolitan area network (MAN).
LAN 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.
WAN 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.
CAN 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.
MAN 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).
If you think that these definitions of LAN, WAN, CAN, and MAN are a bit fuzzy, good! That's because they are! Furthermore, it's likely that they will get fuzzier as time goes on and technology presses forward.
As a consequence of the fuzziness of these terms, we define the term local network to mean the collection of all nodes connected via the same medium and sharing the same network number. We formally define network number in "IPv4 Addressing" on page 108, but for now think of sharing the same network number as meaning that no hardware or software boundaries must be crossed. In other words, nodes that share the same network number can communicate with each other without requiring the services of a router (router is defined in "The Internet Layer" on page 9). The definition of local network given here is synonymous with the definition of link local scope (defined in Chapter 5) and is quite similar to that of broadcast domain, which is defined in "Broadcast Addresses" on page 117.