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.
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.