Domain Name System

From ArticleWorld

The Domain Name System (DNS) is a distributed database that associates domain names on the Internet with IP addresses. It offers the major advantage of allowing Internet sites to have a name associated, rather than just a hard-to-remember IP.

The DNS records are administered by the Network Information Centers. Legal users pay an annual fee in order to use a domain name, but this is often subject to the local regulations. The exact contract type and clauses vary.

How DNS works

The domains of the Internet are recorded in a domain tree divided into zones. A zone is a collection of nodes served by a single DNS server (although a DNS server can serve several zones at the same time). Zones can be delegated to other servers if required.

A special program called resolver communicates with the name servers in order to obtain the IP address associated to a certain domain name. This often requires the resolver to go through multiple name servers in order to obtain the information, a process called recursion.

The domain name

The domain name has a specialized structure. It consists of at least two parts (labels), separated by dots. For example, in the name

  • The rightmost label contains the top-level domain (.org, in this case).
  • Every division to the left represents a subdomain with a relative dependence. is a subdomain of the .org domain, and is a subdomain of the domain. There can be as much as 127 levels of subdivision, as long as the domain name is not longer than 255 characters.
  • A domain that has an associated IP address is a hostname. Note that not all domain names are hostnames, but only those that correspond to a certain host on the Internet.