Every computer connected to the Internet has a unique identity.
This document explains these identifiers, and describes how to find out the IP address and how to find out the host name and domain name of a specific computer. The domain name is the name of a network associated with an organization. In addition to the main mit.edu domain, there is, for example, a domain associated with the Artificial Intelligence Laboratory at MIT, called ai.mit.edu . The use of host name aliases makes it easier for service providers to migrate services to new machines without interrupting service. Or a program which already knows the IP address must determine the domain name for the network to which the machine is connected.