Name Service

When a user enters a command such as ping xena, one of the first things that must happen is translation of the hostname xena to an IP address. This can happen in one of two ways.

The IP address can be determined from the /etc/hosts file, or it can be resolved through a domain name service (DNS). For a small network, using just /etc/hosts is not a problem. For a larger network, trying to keep the /etc/hosts file in sync on all hosts can result in a great deal of work because these files must be exactly the same on each host. If the same address gets used on two different systems, the network could fail.

DNS relies on the named (pronounced name d) server to provide hostname-to-IP address translations. The named server is a host that permanently stores hostname and IP address information for a specific domain. A domain name is the network equivalent of a hostname. A hostname refers to a specific system on the network, and a domain name refers to a specific network. Sites and institutions are assigned a domain name for their network. In turn, they assign hostnames to systems within their domain. The Internet domain name system provides a scheme by which every site in the world has a unique name.

Name services and DNS are discussed again in more detail in Chapter 23.