Domain Name System

The Domain Name System, most often known as simply DNS, is a core feature of the Internet. It is a distributed database that handles the mapping between host names (domain names), which are more convenient for humans, and the numerical IP address, which a computer can use directly.

For example, www.wikipedia.org is a domain name and 130.94.122.199 the corresponding numerical internet address. The domain name system acts much like an automated phone book, so you can "call" www.wikipedia.org instead of 130.94.122.199. So, it converts human-friendly names such as "www.wikipedia.org" into computer-friendly (IP) addresses such as 130.94.122.199.

DNS was first invented in 1983 by Paul Mockapetris; the original specifications are described in RFC 882. In 1987 RFC 1034 and RFC 1035 were published which updated the DNS specifcation and made RFC 882 and RFC 883 obsolete. Subsequent to that there have been quite a few RFCs published that propose various extensions to the core protocols.

DNS implements a hierarchical name space by allowing name service for parts of a name space known as zones to be "delegated" by a name server to subsidiary name-servers. DNS also provides additional information, such as alias names for systems, contact information, and which hosts act as mail hubs for groups of systems or domains.

The present restriction on the length of domain names is 63 characters, excluding the www. and .com or other extension. Domain names are also limited to a subset of ASCII characters, preventing many languages from representing their names and words correctly. The Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, has been approved by ICANN and adopted by some registries as a workaround.

The DNS system is run by various flavors of DNS software, including:

  • BIND (Berkeley Internet Name Domain), the most commonly used namedaemon.
  • DJBDNS (Dan J Bernstein's DNS implementation)
  • MaraDNS
  • NSD (Name Server Daemon)
  • PowerDNS

Any IP computer network can use DNS to implement its own private name system. However, the term "domain name" is most commonly used to refer to domain names implemented in the public Internet DNS system. This is based on thirteen "root servers" worldwide, all but three of which are in the United States of America. From these thirteen root servers, the rest of the Internet DNS name space is delegated to other DNS servers which serve names within specific parts of the DNS name space.

An 'owner' of a domain name can be found by looking in the whois database: for most gTLDs a basic WHOIS is held by ICANN, with the detailed WHOIS maintained by the domain registry which controls that domain. For the 240+ Country Code TLDs the position is usually that the registry holds the entire authorative WHOIS for that extension, as part of their many functions.

The current way the main DNS system is controlled is often criticized. The most common problems pointed at are that it is abused by monopolies or near-monopolies such as VeriSign Inc., and problems with assignment of top-level domains.

Some also allege that many implementations of DNS server software fail to work gracefully with dynamically allocated IP addresses, although that is the failure of specific implementations and not failures of the protocol itself.

DNS uses TCP and UDP ports 53.

See also: cybersquatting, dynamic DNS, ICANN, DNSSEC

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