Domain names

The DNS uses a hierarchical naming convention for naming hosts. Each host name is composed of domain labels separated by periods. Local network administrators have the authority to name local domains within an intranet. Each label represents an increasingly higher domain level within an intranet. The fully qualified domain name of a host connected to one of the larger intranets generally has one or more subdomains:

host.subdomain.subdomain.rootdomain
host.subdomain.rootdomain

Domain names often reflect the hierarchy level used by network administrators to assign domain names. For example, the domain name eng.mit.edu. is the fully qualified domain name, where eng is the host, mit is the subdomain, and edu is the highest level domain (root domain).

Figure 1 is an example of the DNS used in the hierarchy naming structure across an intranet.

Figure 1. Hierarchical naming tree

Example of DNS hierarchy starting with root, some of its children, such as GOV, EDU, and ORG, and their descendants

You can refer to hosts in your domain by host name only; however, a name server requires a fully qualified domain name. The local resolver appends the domain name before sending the query to the Domain Name Server for address resolution.