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A domain name is an identification
string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * Strings (1991 film), ''Strings'' (1991 fil ...
that defines a realm of administrative autonomy, authority or control within the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consist ...

Internet
. Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name identifies a
network domain A network domain is an administrative grouping of multiple private computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of s ...
, or it represents an
Internet Protocol The Internet Protocol (IP) is the network layer communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A communications system or com ...
(IP) resource, such as a personal computer used to access the Internet, a server computer hosting a
website A website (also written as web site) is a collection of web page A web page (or webpage) is a hypertext File:Douglas Engelbart in 2008.jpg, Douglas Engelbart in 2009, at the 40th anniversary celebrations of "The Mother of All Demos" i ...

website
, or the web site itself or any other service communicated via the Internet. In 2017, 330.6 million domain names had been registered. Domain names are formed by the rules and procedures of the
Domain Name System The Domain Name System (DNS) is the hierarchical and decentralized Decentralization or decentralisation is the process by which the activities of an organization, particularly those regarding planning and decision making, are distributed o ...

Domain Name System
(DNS). Any name registered in the DNS is a domain name. Domain names are organized in subordinate levels (subdomains) of the
DNS root The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet The Internet (Capitalization of Internet, or internet) is the global system of int ...
domain, which is nameless. The first-level set of domain names are the
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
s (TLDs), including the
generic top-level domain Generic top-level domains (gTLDs) are one of the categories of top-level domain A top-level domain (TLD) is one of the Domain name, domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. T ...
s (gTLDs), such as the prominent domains com,
info Info is shorthand for "information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of its characteristics. The concept of ''inform ...
,
net Net or net may refer to: Mathematics and physics * Net (mathematics) In mathematics, more specifically in general topology and related branches, a net or Moore–Smith sequence is a generalization of the notion of a sequence. In essence, ...
,
eduEdu or EDU may refer to: People ; Given name or nickname * Edu (footballer, born 1949), Brazilian footballer named Jonas Eduardo Américo * Edu (footballer, born 1974), Brazilian footballer named Eduardo Araújo Moreira * Edu (footballer, born 197 ...
, and
org ORG or org may refer to: Music * ORG Records, an independent record label active from 1986-2008 Organizations * Organization (or organisation), a social entity that has a collective goal and is linked to an external environment * Oxford Research ...
, and the
country code top-level domain A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all tw ...
s (ccTLDs). Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites. The registration of these domain names is usually administered by
domain name registrar A domain name registrar is a company that manages the reservation of Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/I ...
s who sell their services to the public. A
fully qualified domain name A fully qualified domain name (FQDN), sometimes also referred to as an ''absolute domain name'', is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It specifies all domain levels, including t ...
(FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Traditionally a FQDN ends in a dot (.) to denote the top of the DNS tree. Labels in the Domain Name System are
case-insensitiveIn computers, case sensitivity defines whether uppercase and lowercase letters are treated as distinct (case-sensitive) or equivalent (case-insensitive). For instance, when users interested in learning about dogs search an e-book An electronic b ...
, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.


Purpose

Domain names serve to identify Internet resources, such as computers, networks, and services, with a text-based label that is easier to memorize than the numerical addresses used in the Internet protocols. A domain name may represent entire collections of such resources or individual instances. Individual Internet host computers use domain names as host identifiers, also called
hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network A computer network is a group of computers that use a set of common communication protocols over digital signal ...
s. The term ''hostname'' is also used for the leaf labels in the domain name system, usually without further subordinate domain name space. Hostnames appear as a component in
Uniform Resource Locator A Uniform Resource Locator (URL), colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network A computer network is a group of computers that use a set of common communication prot ...

Uniform Resource Locator
s (URLs) for Internet resources such as
websites A website (also written as web site) is a collection of web pages and related content that is identified by a common domain name and published on at least one web server. Notable examples are wikipedia.org, google.com, and amazon.com. All ...

websites
(e.g., en.wikipedia.org). Domain names are also used as simple identification labels to indicate ownership or control of a resource. Such examples are the realm identifiers used in the
Session Initiation Protocol The Session Initiation Protocol (SIP) is a signaling protocolA signaling protocol is a type of communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Commun ...
(SIP), the
Domain KeysDomainKeys (informally ''DK'') is a deprecated e-mail authentication system designed by Yahoo to verify the domain name of an e-mail sender and the message integrity. Aspects of DomainKeys, along with parts of Identified Internet Mail, were combined ...
used to verify DNS domains in
e-mail upThe email_address.html"_;"title="at_sign,_a_part_of_every_SMTP_email_address">at_sign,_a_part_of_every_SMTP_email_address Electronic_mail_(email_or_e-mail)_is_a_method_of_exchanging_messages_("mail")_between_people_using_electronic_dev ...

e-mail
systems, and in many other
Uniform Resource Identifier A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, concep ...
s (URIs). An important function of domain names is to provide easily recognizable and memorizable names to numerically addressed Internet resources. This abstraction allows any resource to be moved to a different physical location in the address topology of the network, globally or locally in an
intranet An intranet is a computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the No ...

intranet
. Such a move usually requires changing the IP address of a resource and the corresponding translation of this IP address to and from its domain name. Domain names are used to establish a unique identity. Organizations can choose a domain name that corresponds to their name, helping Internet users to reach them easily. A generic domain is a name that defines a general category, rather than a specific or personal instance, for example, the name of an industry, rather than a company name. Some examples of generic names are ''books.com'', ''music.com'', and ''travel.info''. Companies have created brands based on generic names, and such generic domain names may be valuable. Domain names are often simply referred to as ''domains'' and domain name registrants are frequently referred to as ''domain owners'', although domain name registration with a registrar does not confer any legal ownership of the domain name, only an exclusive right of use for a particular duration of time. The use of domain names in commerce may subject them to
trademark law A trademark (also written trade mark or trade-markThe styling of ''trademark'' as a single word is predominantly used in the United States and Philippines only, while the two-word styling ''trade mark'' is used in many other countries around ...
.


History

The practice of using a simple memorable abstraction of a host's numerical address on a computer network dates back to the
ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switching In telecommunications, packet switching is a method of grouping data that is transmitted over a digital network into '' packets''. Packets are ...
era, before the advent of today's commercial Internet. In the early network, each computer on the network retrieved the hosts file (''host.txt'') from a computer at SRI (now
SRI International SRI International (SRI) is an American nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public ...
),RFC 3467, ''Role of the Domain Name System (DNS)'', J.C. Klensin, J. Klensin (February 2003) which mapped computer hostnames to numerical addresses. The rapid growth of the network made it impossible to maintain a centrally organized hostname registry and in 1983 the Domain Name System was introduced on the ARPANET and published by the
Internet Engineering Task Force The Internet Engineering Task Force (IETF) is an open standards organization, which develops and promotes voluntary Internet standards, in particular the technical standards that comprise the Internet protocol suite (TCP/IP). It has no formal ...
as RFC 882 and RFC 883. The following table shows the first 20 domains with the dates of their registration:


Domain name space

Today, the
Internet Corporation for Assigned Names and Numbers The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder governance, multistakeholder group and nonprofit organization responsible for coordinating the maintenance and procedures of several databases ...
(ICANN) manages the top-level development and architecture of the Internet domain name space. It authorizes
domain name registrar A domain name registrar is a company that manages the reservation of Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/I ...
s, through which domain names may be registered and reassigned. The domain name space consists of a
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...
of domain names. Each node in the tree holds information associated with the domain name. The tree sub-divides into ''zones'' beginning at the
DNS root zone The DNS root zone is the top-level DNS zone A DNS zone is any distinct, contiguous portion of the domain name space in the Domain Name System The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, serv ...
.


Domain name syntax

A domain name consists of one or more parts, technically called ''labels'', that are conventionally concatenated, and delimited by dots, such as ''
example.com The domain names example.com, example.net, example.org, and example.edu are second-level domain In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a top-level domain (TLD). For example, ...
''. * The right-most label conveys the
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
; for example, the domain name ''www.example.com'' belongs to the top-level domain ''com''. * The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or
subdomain In the Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, Internet#Applications_and_services, services, and other resources reachable through ...

subdomain
of the domain to the right. For example: the label ''example'' specifies a node ''example.com'' as a subdomain of the ''com'' domain, and ''www'' is a label to create ''www.example.com'', a subdomain of ''example.com''. Each label may contain from 1 to 63 octets. The empty label is reserved for the root node and when fully qualified is expressed as the empty label terminated by a
dot
dot
. The full domain name may not exceed a total length of 253 ASCII characters in its textual representation.RFC 1035, ''Domain names--Implementation and specification'', P. Mockapetris (Nov 1987) Thus, when using a single character per label, the limit is 127 levels: 127 characters plus 126 dots have a total length of 253. In practice, some domain registries may have shorter limits. * A
hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network A computer network is a group of computers that use a set of common communication protocols over digital signal ...
is a domain name that has at least one associated IP address. For example, the domain names ''www.example.com'' and ''example.com'' are also hostnames, whereas the ''com'' domain is not. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames. * Hostnames impose restrictions on the characters allowed in the corresponding domain name. A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname.


Top-level domains

When the Domain Name System was devised in the 1980s, the domain name space was divided into two main groups of domains. The
country code top-level domain A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all tw ...
s (ccTLD) were primarily based on the two-character territory codes of
ISO-3166 ISO 3166 is a standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined ...
country abbreviations. In addition, a group of seven
generic top-level domain Generic top-level domains (gTLDs) are one of the categories of top-level domain A top-level domain (TLD) is one of the Domain name, domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. T ...
s (gTLD) was implemented which represented a set of categories of names and multi-organizations. These were the domains
gov A government is the system or group of people governing an organized community, generally a State (polity), state. In the case of its broad associative definition, government normally consists of legislature, Executive (government), ex ...
,
eduEdu or EDU may refer to: People ; Given name or nickname * Edu (footballer, born 1949), Brazilian footballer named Jonas Eduardo Américo * Edu (footballer, born 1974), Brazilian footballer named Eduardo Araújo Moreira * Edu (footballer, born 197 ...
, com, mil,
org ORG or org may refer to: Music * ORG Records, an independent record label active from 1986-2008 Organizations * Organization (or organisation), a social entity that has a collective goal and is linked to an external environment * Oxford Research ...
,
net Net or net may refer to: Mathematics and physics * Net (mathematics) In mathematics, more specifically in general topology and related branches, a net or Moore–Smith sequence is a generalization of the notion of a sequence. In essence, ...
, and int. These two types of
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
s (TLDs) are the highest level of domain names of the Internet. Top-level domains form the
DNS root zone The DNS root zone is the top-level DNS zone A DNS zone is any distinct, contiguous portion of the domain name space in the Domain Name System The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, serv ...
of the hierarchical
Domain Name System The Domain Name System (DNS) is the hierarchical and decentralized Decentralization or decentralisation is the process by which the activities of an organization, particularly those regarding planning and decision making, are distributed o ...

Domain Name System
. Every domain name ends with a top-level domain label. During the growth of the Internet, it became desirable to create additional generic top-level domains. As of October 2009, 21 generic top-level domains and 250 two-letter country-code top-level domains existed. In addition, the ARPA domain serves technical purposes in the infrastructure of the Domain Name System. During the 32nd International Public ICANN Meeting in Paris in 2008, ICANN started a new process of TLD naming policy to take a "''significant step forward on the introduction of new generic top-level domains''." This program envisions the availability of many new or already proposed domains, as well as a new application and implementation process. Observers believed that the new rules could result in hundreds of new top-level domains to be registered. In 2012, the program commenced, and received 1930 applications. By 2016, the milestone of 1000 live gTLD was reached. The
Internet Assigned Numbers Authority The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network A computer ne ...
(IANA) maintains an annotated list of top-level domains in the
DNS root zone The DNS root zone is the top-level DNS zone A DNS zone is any distinct, contiguous portion of the domain name space in the Domain Name System The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, serv ...
database. For special purposes, such as network testing, documentation, and other applications, IANA also reserves a set of special-use domain names. This list contains domain names such as
example Example may refer to: * ''exempli gratia Notes and references Notes References Sources * * * Further reading * * {{Latin phrases E ...'' (e.g.), usually read out in English as "for example" * .example, reserved as a domain na ...
,
local Local may refer to: Geography and transportation * Local (train), a train serving local traffic demand * Local, Missouri, a community in the United States * Local government, a form of public administration, usually the lowest tier of administrati ...
,
localhost In computer networking A computer network is a group of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of op ...
, and
test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * Test (2013 film), ''Test'' (2013 film), an American film * Test ( ...
. Other top-level domain names containing trade marks are registered for corporate use. Cases include brands such as
BMW Bayerische Motoren Werke AG, commonly referred to as BMW (), is a German multinational corporation which produces luxury vehicle A luxury car is a car A car (or automobile) is a wheeled motor vehicle used for transportation. Most defi ...

BMW
,
Google Google LLC is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational stat ...

Google
, and
Canon Canon or Canons may refer to: Places * Canon, Georgia Canon is a city in Franklin County, Georgia, Franklin and Hart County, Georgia, Hart counties in the U.S. state of Georgia (U.S. state), Georgia. The population was 804 at the 2010 census. His ...
.


Second-level and lower level domains

Below the top-level domains in the domain name hierarchy are the
second-level domain In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a top-level domain (TLD). For example, in , is the second-level domain of the TLD. Second-level domains commonly refer to the organi ...
(SLD) names. These are the names directly to the left of .com, .net, and the other top-level domains. As an example, in the domain ''example.co.uk'', ''co'' is the second-level domain. Next are third-level domains, which are written immediately to the left of a second-level domain. There can be fourth- and fifth-level domains, and so on, with virtually no limitation. An example of an operational domain name with four levels of domain labels is ''sos.state.oh.us''. Each label is separated by a
full stop The full stop (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the ...

full stop
(dot). 'sos' is said to be a sub-domain of 'state.oh.us', and 'state' a sub-domain of 'oh.us', etc. In general,
subdomain In the Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, Internet#Applications_and_services, services, and other resources reachable through ...

subdomain
s are domains subordinate to their parent domain. An example of very deep levels of subdomain ordering are the
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

IPv6
reverse resolution
DNS zone A DNS zone is any distinct, contiguous portion of the domain name space in the Domain Name System The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Int ...
s, e.g., 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa, which is the reverse DNS resolution domain name for the IP address of a
loopback Loopback (also written loop-back) is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure. There are ma ...
interface, or the
localhost In computer networking A computer network is a group of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of op ...
name. Second-level (or lower-level, depending on the established parent hierarchy) domain names are often created based on the name of a company (e.g., ''bbc''.co.uk), product or service (e.g. ''hotmail''.com). Below these levels, the next domain name component has been used to designate a particular host server. Therefore, ''ftp.example.com'' might be an FTP server, ''www.example.com'' would be a
World Wide Web The World Wide Web (WWW), commonly known as the Web, is an information system An information system (IS) is a formal, sociotechnical Sociotechnical systems (STS) in organizational development is an approach to complex organizational ...
server, and ''mail.example.com'' could be an email server, each intended to perform only the implied function. Modern technology allows multiple physical servers with either different (cf. load balancing) or even identical addresses (cf.
anycast Anycast is a network addressing In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a computer data storage, memory cell or other logical or physical ...

anycast
) to serve a single hostname or domain name, or multiple domain names to be served by a single computer. The latter is very popular in
Web hosting service A web hosting service is a type of Internet hosting service The Internet ( or internet) is the global system of interconnected computer network A computer network is a group of computers that use a set of common communication ...
centers, where service providers host the websites of many organizations on just a few servers. The hierarchical
DNS label The Domain Name System (DNS) is the hierarchical and naming system used to identify computers, , and other resources reachable through the or other networks. The contained in the DNS associate s with other forms of information. These are m ...
s or components of domain names are separated in a fully qualified name by the
full stop The full stop (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the ...

full stop
(dot, ''.'').


Internationalized domain names

The character set allowed in the Domain Name System is based on
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the stu ...
and does not allow the representation of names and words of many languages in their native scripts or alphabets.
ICANN The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder group and nonprofit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or no ...

ICANN
approved the
Internationalized domain name An internationalized domain name (IDN) is an Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, a ...
(IDNA) system, which maps
Unicode Unicode, formally the Unicode Standard, is an information technology standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requireme ...

Unicode
strings used in application user interfaces into the valid DNS character set by an encoding called
PunycodePunycode is a representation of Unicode Unicode is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expressed in most of the world ...
. For example, københavn.eu is mapped to xn--kbenhavn-54a.eu. Many registries have adopted IDNA.


Domain name registration


History

The first commercial Internet domain name, in the TLD ''com'', was registered on 15 March 1985 in the name symbolics.com by Symbolics Inc., a computer systems firm in Cambridge, Massachusetts. By 1992, fewer than 15,000 ''com'' domains had been registered. In the first quarter of 2015, 294 million domain names had been registered.Internet Grows to 294 Million Domain Names in the First Quarter of 2015
Jun 30, 2015.
A large fraction of them are in the ''com'' TLD, which as of December 21, 2014, had 115.6 million domain names, including 11.9 million online business and e-commerce sites, 4.3 million entertainment sites, 3.1 million finance related sites, and 1.8 million sports sites. As of July 2012 the ''com'' TLD had more registrations than all of the ccTLDs combined.


Administration

The right to use a domain name is delegated by
domain name registrar A domain name registrar is a company that manages the reservation of Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/I ...
s, which are accredited by the
Internet Corporation for Assigned Names and Numbers The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder governance, multistakeholder group and nonprofit organization responsible for coordinating the maintenance and procedures of several databases ...
(ICANN), the organization charged with overseeing the name and number systems of the Internet. In addition to ICANN, each top-level domain (TLD) is maintained and serviced technically by an administrative organization operating a registry. A registry is responsible for maintaining the database of names registered within the TLD it administers. The registry receives registration information from each domain name registrar authorized to assign names in the corresponding TLD and publishes the information using a special service, the
WHOIS WHOIS (pronounced as the phrase "who is") is a query and response protocol that is widely used for querying database In computing, a database is an organized collection of Data (computing), data stored and accessed electronically from a compu ...
protocol. Registries and registrars usually charge an annual fee for the service of delegating a domain name to a user and providing a default set of name servers. Often, this transaction is termed a sale or lease of the domain name, and the registrant may sometimes be called an "owner", but no such legal relationship is actually associated with the transaction, only the exclusive right to use the domain name. More correctly, authorized users are known as "registrants" or as "domain holders".
ICANN The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder group and nonprofit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or no ...

ICANN
publishes the complete list of TLD registries and domain name registrars. Registrant information associated with domain names is maintained in an online database accessible with the WHOIS protocol. For most of the 250
country code top-level domain A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all tw ...
s (ccTLDs), the domain registries maintain the WHOIS (Registrant, name servers, expiration dates, etc.) information. Some domain name registries, often called ''network information centers'' (NIC), also function as registrars to end-users. The major generic top-level domain registries, such as for the ''com'', ''net'', ''org'', ''info'' domains and others, use a registry-registrar model consisting of hundreds of domain name registrars (see lists at ICANN or VeriSign). In this method of management, the registry only manages the domain name database and the relationship with the registrars. The ''registrants'' (users of a domain name) are customers of the registrar, in some cases through additional layers of resellers. There are also a few other
alternative DNS root The Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''network of ...
providers that try to compete or complement ICANN's role of domain name administration, however, most of them failed to receive wide recognition, and thus domain names offered by those alternative roots cannot be used universally on most other internet-connecting machines without additional dedicated configurations.


Technical requirements and process

In the process of registering a domain name and maintaining authority over the new name space created, registrars use several key pieces of information connected with a domain: * ''Administrative contact''. A registrant usually designates an administrative contact to manage the domain name. The administrative contact usually has the highest level of control over a domain. Management functions delegated to the administrative contacts may include management of all business information, such as name of record, postal address, and contact information of the official registrant of the domain and the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name. Furthermore, the administrative contact installs additional contact information for technical and billing functions. * ''Technical contact''. The technical contact manages the name servers of a domain name. The functions of a technical contact include assuring conformance of the configurations of the domain name with the requirements of the domain registry, maintaining the domain zone records, and providing continuous functionality of the name servers (that leads to the accessibility of the domain name). * ''Billing contact''. The party responsible for receiving billing invoices from the
domain name registrar A domain name registrar is a company that manages the reservation of Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/I ...
and paying applicable fees. * ''Name servers''. Most registrars provide two or more name servers as part of the registration service. However, a registrant may specify its own
authoritative name server A name server refers to the server component of the Domain Name System The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet The Interne ...
s to host a domain's resource records. The registrar's policies govern the number of servers and the type of server information required. Some providers require a hostname and the corresponding IP address or just the hostname, which must be resolvable either in the new domain, or exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required. A domain name consists of one or more labels, each of which is formed from the set of ASCII letters, digits, and hyphens (a-z, A-Z, 0–9, -), but not starting or ending with a hyphen. The labels are case-insensitive; for example, 'label' is equivalent to 'Label' or 'LABEL'. In the textual representation of a domain name, the labels are separated by a
full stop The full stop (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the ...

full stop
(period).


Business models

Domain names are often seen in analogy to
real estate Real estate is property consisting of land and the buildings on it, along with its natural resource , Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and feder ...

real estate
in that domain names are foundations on which a website can be built, and the highest ''quality'' domain names, like sought-after real estate, tend to carry significant value, usually due to their online brand-building potential, use in advertising,
search engine optimization Search engine optimization (SEO) is the process of improving the quality and quantity of website traffic to a website A website (also written as web site) is a collection of web page A web page (or webpage) is a hypertext File:D ...
, and many other criteria. A few companies have offered low-cost, below-cost or even free domain registration with a variety of models adopted to recoup the costs to the provider. These usually require that domains be hosted on their website within a framework or portal that includes advertising wrapped around the domain holder's content, revenue from which allows the provider to recoup the costs. Domain registrations were free of charge when the DNS was new. A domain holder may provide an infinite number of
subdomain In the Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, Internet#Applications_and_services, services, and other resources reachable through ...

subdomain
s in their domain. For example, the owner of ''example.org'' could provide subdomains such as ''foo.example.org'' and ''foo.bar.example.org'' to interested parties. Many desirable domain names are already assigned and users must search for other acceptable names, using Web-based search features, or
WHOIS WHOIS (pronounced as the phrase "who is") is a query and response protocol that is widely used for querying database In computing, a database is an organized collection of Data (computing), data stored and accessed electronically from a compu ...
and
dig Digging, also referred to as excavation, is the process of using some implement such as claw A domestic cat's retractable claw in protracted position A claw is a curved, pointed appendage found at the end of a toe or finger in most amniote ...
operating system tools. Many registrars have implemented domain name suggestion tools which search domain name databases and suggest available alternative domain names related to keywords provided by the user.


Resale of domain names

The business of resale of registered domain names is known as the domain aftermarket. Various factors influence the perceived value or market value of a domain name. Most of the high-prize domain sales are carried out privately.


Domain name confusion

Intercapping is often used to emphasize the meaning of a domain name, because DNS names are not case-sensitive. Some names may be misinterpreted in certain uses of capitalization. For example: ''Who Represents'', a database of artists and agents, chose ''whorepresents.com'', which can be misread. In such situations, the proper meaning may be clarified by placement of hyphens when registering a domain name. For instance, Experts Exchange, a programmers' discussion site, used ''expertsexchange.com'', but changed its domain name to ''experts-exchange.com''.


Use in web site hosting

The domain name is a component of a
uniform resource locator A Uniform Resource Locator (URL), colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network A computer network is a group of computers that use a set of common communication prot ...

uniform resource locator
(URL) used to access
web site A website (also written as web site) is a collection of web pages and related content that is identified by a common domain name A domain name is an identification string that defines a realm of administrative autonomy, authority or control ...
s, for example: *URL: http://www.example.net/index.html *Top-level domain: net *Second-level domain: example *Hostname: www A domain name may point to multiple
IP addresses An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet prot ...
to provide server redundancy for the services offered, a feature that is used to manage the traffic of large, popular web sites.
Web hosting services A web hosting service (often shortened to web host) is a type of Internet hosting service that allows individuals and organizations to make their website accessible via the World Wide Web. Web hosts are companies that provide space on a server ...
, on the other hand, run servers that are typically assigned only one or a few addresses while serving websites for many domains, a technique referred to as virtual web hosting. Such IP address overloading requires that each request identifies the domain name being referenced, for instance by using the HTTP request header field ''Host:'', or
Server Name Indication Server Name Indication (SNI) is an extension to the Transport Layer Security Transport Layer Security (TLS), and its now-deprecated predecessor, Secure Sockets Layer (SSL), are cryptographic protocols designed to provide communications security o ...
.


Abuse and regulation

Critics often claim abuse of administrative power over domain names. Particularly noteworthy was the
VeriSign
VeriSign
Site Finder system which redirected all unregistered .com and .net domains to a VeriSign webpage. For example, at a public meeting with VeriSign to air technical concerns about SiteFinder, numerous people, active in the
IETF The Internet Engineering Task Force (IETF) is an open standards organization, which develops and promotes voluntary Internet standards, in particular the technical standards that comprise the Internet protocol suite (TCP/IP). It has no formal ...
and other technical bodies, explained how they were surprised by VeriSign's changing the fundamental behavior of a major component of Internet infrastructure, not having obtained the customary consensus. SiteFinder, at first, assumed every Internet query was for a website, and it monetized queries for incorrect domain names, taking the user to VeriSign's search site. Unfortunately, other applications, such as many implementations of email, treat a lack of response to a domain name query as an indication that the domain does not exist, and that the message can be treated as undeliverable. The original VeriSign implementation broke this assumption for mail, because it would always resolve an erroneous domain name to that of SiteFinder. While VeriSign later changed SiteFinder's behaviour with regard to email, there was still widespread protest about VeriSign's action being more in its financial interest than in the interest of the Internet infrastructure component for which VeriSign was the steward. Despite widespread criticism, VeriSign only reluctantly removed it after the
Internet Corporation for Assigned Names and Numbers The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder governance, multistakeholder group and nonprofit organization responsible for coordinating the maintenance and procedures of several databases ...
(ICANN) threatened to revoke its contract to administer the root name servers. ICANN published the extensive set of letters exchanged, committee reports, and ICANN decisions. There is also significant disquiet regarding the United States Government's political influence over ICANN. This was a significant issue in the attempt to create a .xxx
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
and sparked greater interest in
alternative DNS root The Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''network of ...
s that would be beyond the control of any single country. Additionally, there are numerous accusations of domain name front running, whereby registrars, when given whois queries, automatically register the domain name for themselves. Network Solutions has been accused of this.


Truth in Domain Names Act

In the United States, the
Truth in Domain Names Act The PROTECT Act of 2003 (, 117 Stat. 650, S. 151, enacted April 30, 2003) is a United States law with the stated intent of preventing child abuse as well as investigating and prosecuting violent crimes against children. "PROTECT" is a contrived ac ...
of 2003, in combination with the
PROTECT Act of 2003 The PROTECT Act of 2003 (, 117 Stat. 650, S. 151, enacted April 30, 2003) is a United States law with the stated intent of preventing child abuse as well as investigating and prosecuting violent crimes against children. "PROTECT" is a contrived ac ...
, forbids the use of a misleading domain name with the intention of attracting Internet users into visiting
Internet pornography Internet pornography is any pornography that is accessible over the internet, primarily via websites, peer-to-peer file sharing, or Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed f ...
sites. The Truth in Domain Names Act follows the more general
Anticybersquatting Consumer Protection ActThe Anticybersquatting Consumer Protection Act (ACPA), 15 U.S.C. § 1125(d),(passed as part of ) is a U.S. law enacted in 1999 that established a cause of action for registering, trafficking in, or using a domain name confusingly similar to, or di ...
passed in 1999 aimed at preventing
typosquatting Typosquatting, also called URL hijacking, a sting site, or a fake URL, is a form of cybersquatting, and possibly brandjacking which relies on mistakes such as typographical error, typos made by Internet users when inputting a URL, website address ...

typosquatting
and deceptive use of names and trademarks in domain names.


Seizures

File:Absolutepoker.png, absolutepoker.com File:Website seizure notice.jpg, channelsurfing.net File:Liberty Reserve seizure notice.png, In the early 21st century, the US Department of Justice (DOJ) pursued the
seizure An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temp ...
of domain names, based on the legal theory that domain names constitute property used to engage in criminal activity, and thus are subject to forfeiture. For example, in the seizure of the domain name of a gambling website, the DOJ referenced and .
In 2013 the US government seized
Liberty Reserve Liberty Reserve was a Costa Rica Costa Rica (, ; ; literally "Rich Coast"), officially the Republic of Costa Rica ( es, República de Costa Rica), is a country in Central America, bordered by Nicaragua Nicaragua (; ), officially the ...

Liberty Reserve
, citing . The U.S. Congress passed the
Combating Online Infringement and Counterfeits Act United States Senate Bill S.3804, known as the Combating Online Infringement and Counterfeits Act (COICA) was a bill introduced by Senator Patrick Leahy Patrick Joseph Leahy (; born March 31, 1940) is an American politician and attorney servin ...
in 2010. Consumer Electronics Association vice president Michael Petricone was worried that seizure was a ''blunt instrument'' that could harm legitimate businesses. After a joint operation on February 15, 2011, the DOJ and the Department of Homeland Security claimed to have seized ten domains of websites involved in advertising and distributing child pornography, but also mistakenly seized the domain name of a large DNS provider, temporarily replacing 84,000 websites with seizure notices. In the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shorth ...

United Kingdom
, the
Police Intellectual Property Crime Unit The Police Intellectual Property Crime Unit (PIPCU) is a department of the City of London Police, the national lead force for fraud. It was established in 2013 with the responsibility to investigate and deter serious and organised intellectual prope ...
has been attempting to seize domain names from registrars without court orders.


Suspensions

PIPCU and other UK law enforcement organisations make domain suspension requests to Nominet which they process on the basis of breach of terms and conditions. Around 16,000 domains are suspended annually, and about 80% of the requests originate from PIPCU.


Property rights

Because of the economic value it represents, the European Court of Human Rights has ruled that the exclusive right to a domain name is protected as property under article 1 of Protocol 1 to the European Convention on Human Rights.


IDN Variants

ICANN The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder group and nonprofit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or no ...

ICANN
Business Constituency (BC) has spent decades trying to make IDN variants work at the second level, and in the last several years at the top level. Domain name variants are domain names recognized in different character encodings, like a single domain presented in Traditional_Chinese_characters, traditional Chinese and Simplified_Chinese_characters, simplified Chinese. It is an Internationalization and localization problem. Under Domain Name Variants, the different encodings of the domain name (in simplified and traditional Chinese) would resolve to the same host. According to John_R._Levine, John Levine, an expert on Internet related topics, ''"Unfortunately, variants don't work. The problem isn't putting them in the DNS, it's that once they're in the DNS, they don't work anywhere else."''


Fictitious domain name

A ''fictitious domain name'' is a domain name used in a work of fiction or popular culture to refer to a domain that does not actually exist, often with invalid or unofficial
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
s such as ".web", a usage exactly analogous to the dummy 555 (telephone number), 555 telephone number prefix used in film and other media. The canonical fictitious domain name is "
example.com The domain names example.com, example.net, example.org, and example.edu are second-level domain In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a top-level domain (TLD). For example, ...
", specifically set aside by IANA in RFC 2606 for such use, along with the ''.example'' TLD. Domain names used in works of fiction have often been registered in the DNS, either by their creators or by Cybersquatting, cybersquatters attempting to profit from it. This phenomenon prompted NBC to purchase the domain name Hornymanatee.com after talk-show host Conan O'Brien spoke the name while ad-libbing on Late Night with Conan O'Brien, his show. O'Brien subsequently created a website based on the concept and used it as a running gag on the show.


Domain name spoofing

The term Domain name spoofing (or simply though less accurately, Domain spoofing) is used generically to describe one or more of a class of phishing attacks that depend on falsifying or misrepresenting an internet domain name. These are designed to persuade unsuspecting users into visiting a web site other than that intended, or opening an email that is not in reality from the address shown (or apparently shown). Although website and email spoofing attacks are more widely known, any service that relies on Name resolution (computer systems), domain name resolution may be compromised.


Types

There are a number of better-known types of domain spoofing: * Typosquatting also called "URL hijacking", a "sting site", or a "fake URL", is a form of cybersquatting, and possibly brandjacking which relies on mistakes such as typographical error, typos made by Internet users when inputting a URL, website address into a web browser or composing an email address. Should a user accidentally enter an incorrect domain name, they may be led to any URL (including an alternative website owned by a cybersquatter). :The typosquatter's Uniform Resource Locator, URL will usually be one of five kinds, all ''similar to'' the victim site address: :*A common misspelling, or foreign language spelling, of the intended site :*A misspelling based on a typographical error :*A plural of a singular domain name :*A different
top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, ...
: (i.e. .com instead of .org) :*An abuse of the country code top-level domain, Country Code Top-Level Domain (ccTLD) (.cm, .co, or .om instead of .com) * IDN homograph attack, Internationalised domain name homograph attack. This type of attack depends on registering a domain name that is similar to the 'target' domain, differing from it only because its spelling includes one or more characters that come from a different alphabet but look the same to the naked eye. For example, the Cyrillic, Latin, and Greek alphabet, Greek alphabets each have their own letter , each of which has its own binary code point. Turkish (language), Turkish has a Dotless I, dotless letter i () that may not be perceived as different from the ASCII letter . Most web browsers warn of 'mixed alphabet' domain names, Other services, such as email applications, may not provide the same protection. Reputable top level domain and CCTLD, country code domain registrars will not accept applications to register a deceptive name but this policy cannot be presumed to be infallible. * * *


Risk mitigation

* * * ("Domain-based Message Authentication, Reporting and Conformance") * * (SSL certificate)


Legitimate technologies that may be subverted

* *


See also

* Domain hack * Domain hijacking * Domain name registrar * Domain name speculation * Domain name warehousing * Domain registration * Domain tasting * Geodomain * List of Internet top-level domains * Reverse domain hijacking * Reverse domain name notation


References


External links


(domain bias in web search) a research by Microsoft Top Level Domain Bias in Search Engine Indexing and Rankings
*
Icann New gTLD Program Factsheet - October 2009
(PDF)
IANA Two letter Country Code TLD

ICANN
- Internet Corporation for Assigned Names and Numbers
Internic.net
public information regarding Internet domain name registration services
Internet Domain Names: Background and Policy Issues
Congressional Research Service * , Domain Names — Concepts and Facilities, an Internet Protocol Standard * , Domain Names — Implementation and Specification, an Internet Protocol Standard
UDRP
Uniform Domain-Name Dispute-Resolution Policy
Special use domain names
{{Authority control Domain Name System, * Domain names, Identifiers