NetBEUI
Despite the prominence of TCP/IP and the other protocols already discussed in this chapter, other protocols are used—and you can expect to encounter them at some point. One such protocol is NetBEUI. NetBEUI is a simple but fast protocol that was designed by Microsoft and IBM in the mid-1980s. The speed of NetBEUI can be attributed to the fact that it has very little overhead, but this fact in turn means that NetBEUI has limited functionality. Although it is not commonly used, NetBEUI has found a niche in small networks, such as those in home offices and small businesses.
The biggest limitation of the NetBEUI protocol is that it is not routable. Thus, an organization that requires more than a single segment cannot use NetBEUI. Bridges can be used to divide up a network that uses NetBEUI, but in reality few people bother to do this anymore and instead just use a protocol such as TCP/IP.
Mapping NetBEUI to the OSI Model
NetBEUI is a very simplistic network protocol and as such does not map to many layers of the OSI model. Specifically, the NetBEUI protocol operates only at the transport and network layers of the OSI model. Because NetBEUI operates at only two layers, other protocols are needed to help in the network communication process. NetBEUI requires NetBIOS, which maps to the session layer of the OSI model, to establish a connection between two network devices; it needs a redirector to allow client systems to see network resources; and it needs the Server Message Block (SMB) protocol, which maps to the presentation layer of the OSI model, to provide communication between client redirectors and network servers.
NetBEUI Addressing
Compared to the addressing schemes of IPX/SPX and TCP/IP, NetBEUI's is very simple. NetBEUI allows the computers on a network to be identified by NetBIOS name. The NetBIOS, or friendly, name must be no more than 15 characters in length, and it must be unique to the network. A NetBIOS name can be made up of any combination of characters, with the exclusion of certain special characters such as spaces (in Windows 2000).
NOTE
FQDN As of Windows 2000, Microsoft has moved away from the NetBEUI addressing scheme described here. Instead of the 15-character naming, Windows 2000 uses the fully qualified domain name (FQDN) of the system.
You can create NetBEUI names such as workstation1 and fileserver. As you can imagine, such a scheme works well in small environments that don't have many systems; in the few cases where you come across NetBEUI, they will be in exactly these kinds of environments.
NetBEUI was designed and is very well suited for small networks that have no need for routing. Its ease of configuration and maintenance also make it suitable for network environments in which administrative support is not always accessible. At the end of the day, however, its limitations exclude it from most networking environments, and therefore it is becoming extinct.