Therefore, the main purpose of a free domain name is to provide a recognizable name to mostly numerically addressed Internet resources. It allows any resource, and in this case a website, to be moved to a different physical location in the network globally. The DNS is a hierarchical naming system for computers, services, or any resource participating in the Internet. Its purpose is to associates various information with domain names assigned to such participants and translate them for the purpose of locating and addressing these devices world-wide. This system thus makes it possible to assign domain names to groups of Internet users in a meaningful way, independent of each user's physical location. It is an essential component of the functionality of the Internet. It stores other types of information, such as the list of mail servers that accept email for a given Internet domain.

It is the DNS distributes the responsibility of assigning domain names and mapping those names to Internet Protocol addresses by designating authoritative name servers for each domain. It is here that the idea of free domain comes in. Normally, authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains, essentially, they usually charge for this service. However, there are projects developed to provide Free Domain Names or Free Sub-domain domain name to those who wish to get a customized and free domain name, free sub-domain or free short Uniform Resource Locator (URL) that looks like a real paid domain name. a URL is a type of Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it. In popular language, a URL is also referred to as a Web address.

A person then uses this free domain name to access his website, no matter where it is hosted. This is usually a combination of the host's local name with its parent domain's name. For example, “free.tools.domain.com” would consists of a free local hostname “free”, the local hostname “tools”, which now actually hosts the person with the free domain name and the domain name "domain.com". This is then translated into an IP address through the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a person to have several free domain names, unless there is some regulation from parent host that is providing the free hosting. It is also possible for the single host computer to have several hostnames; but generally the operating system of the host prefers to have one hostname that the host uses for itself.
http://www.dom.ir/