Domain Name System
The Domain Name System, most often known as simply DNS, is a core feature of the Internet. It consists of a distributed database that handles the mapping between host names (domain names), which humans find more convenient, and the numerical IP address, which a computer can use directly.
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2 Delegation 3 The Internet DNS system 4 Politics 5 Criticisms 6 US Truth in Domain Names Act 7 External links |
A domain name such as www.wikipedia.org can form part of a URL such as http://www.wikipedia.org/wiki/Train; or it can form part of an e-mail address such as apache@www.wikipedia.org. That domain name has a corresponding numerical internet address: 130.94.122.199. The domain name system acts much like an automated phone book, so users can "call" www.wikipedia.org instead of 130.94.122.199. In other words, the system converts human-friendly names such as "www.wikipedia.org" into computer-friendly IP addresses such as 130.94.122.199. Virtual hosting allows multiple domain names to be mapped onto a single IP address.
In spite of the similarity in notation of IP addresses and domain names (both having parts separated by dots) the hierarchy in an IP address operates from left to right and in a domain name from right to left.
The domain name consists of two or more parts. From right to left each part specifies a further subdivision, with the top-level domain (the root), for example: com, net, or org, at the right. A second-level domain consists of two parts, e.g. wikipedia.org. The owner of a registered domain can then use or assign further domains, called subdomains: e.g. nl.wikipedia.org (third level domain) or some.other.stuff.wikipedia.org (fifth level domain).
Many domain names used for web sites have 'www' at the left, but the domain name system does not require this. If not, they usually map to the same address as the 'www.'-prefixed equivalents, thus 'ns.nl' maps to 'www.ns.nl'. However, one cannot always omit the 'www.' prefix. Some domain names have 'www' not as the final but the second-last element, for example; www.com, www.ru, www.kz.
Paul Mockapetris first invented DNS in 1983; the original specifications appear in RFC 882. In 1987 the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Subsequent to that several published RFCs have proposed various extensions to the core protocols.
DNS implements a hierarchical name space by allowing a name server to "delegate" name service for parts of a name space (known as "zones") 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.
Currently the length of domain names must not exceed 63 characters (excluding the www. and .com or other extension). Domain names must also use only a subset of ASCII characters, preventing many languages from representing their names and words natively. ICANN has approved the Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, as a workaround to this issue, and some registries have adopted IDNA.
Various flavors of DNS software implement the DNS system, including:
Any IP computer network can use DNS to implement its own private name system. However, the term "domain name" most commonly refers to domain names implemented in the public Internet DNS system.
This builds on thirteen "root servers" worldwide, which distribute their IP addresses independently of the DNS by using a "root hints" file. These root servers delegate the rest of the Internet DNS name space to other DNS servers, which serve names within specific parts of the DNS name space.
The United States of America hosts, at least nominally, all but three of the root servers. However, because many root servers actually implement anycast, where many different computers can share the same IP address to deliver a single service over a large geographic region, most of the physical (rather than nominal) root servers now operate outside the United States.
One can find the 'owner' of a domain name by looking in the whois database: for most gTLDs ICANN holds a basic WHOIS, with the detailed WHOIS maintained by the domain registry which controls that domain.
For the 240+ Country Code top-level domains (TLDs) the registries usually holds the entire authoritative WHOIS for that extension, as part of their many functions.
Many investigators have voiced criticism of the methods used currently to control the main DNS system.
Most commonly, critics claim abuse by monopolies or near-monopolies such as VeriSign Inc., and problems with assignment of top-level domains. The international body ICANN (the Internet Corporation For Assigned Names and Numbers) oversees the domain name industry: see the icann.org website
Some also allege that many implementations of DNS server software fail to work gracefully with dynamically allocated IP addresses: such failure inheres in specific implementations and not in the protocol itself.
See also: cybersquatting, dynamic DNS, ICANN, DNSSEC
The US Truth in Domain Names Act, in combination with the PROTECT Act, forbids knowingly using a misleading domain name with the intent to attract people into viewing a visual depiction of sexually explicit conduct on the Internet.
Overview
Popularity of 'www' as a subdomain
Delegation
DNS uses TCP and UDP ports 53 to serve requests.The Internet DNS system
Politics
Criticisms
US Truth in Domain Names Act
External links