Linux in a Nutshell, Fourth Edition

Overview of Networking

Networks connect computers so that the different systems can share information. For users and system administrators, Unix systems have traditionally provided a set of simple but valuable network services that let you check whether systems are running, refer to files residing on remote systems, communicate via electronic mail, and so on.

For most commands to work over a network, each system must be continuously running a server process in the background, silently waiting to handle the user’s request. This kind of process is called a daemon . Common examples, on which you rely for the most basic functions of your Linux system, are named (which translates between numeric IP addresses and more human-readable alphanumeric names), lpd (which sends documents to a printer, possibly over a network), and ftpd (which allows you to connect to another machine via ftp).

Most Unix networking commands are based on Internet protocols. These are standardized ways of communicating across a network on hierarchical layers. The protocols range from addressing and packet routing at a relatively low layer to finding users and executing user commands at a higher layer.

The basic user commands that most systems support over Internet protocols are generally called TCP/IP commands, named after the two most common protocols. You can use all of these commands to communicate with other Unix systems besides Linux systems. Many can also be used to communicate with non-Unix systems, as a ...