Top Level Domain
A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com. Responsibility of management of most top-level domains is delegated to specific organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA), and is in charge of maintaining the DNS root zone.
Types of TLDs
IANA today distinguishes the following groups of top-level domains:
country-code top-level domains (ccTLD): Two-letter domains established for countries or territories. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
internationalized country code top-level domains (IDN ccTLD): ccTLDs in non-Latin character sets (e.g., Arabic or Chinese).
Test IDN TLDs were installed under test for testing purposes in the IDN development process.
generic top-level domains (gTLD): Top-level domains with three or more characters
unsponsored top-level domains: domains that operate directly under policies established by ICANN processes for the global Internet community.
sponsored top-level domains (sTLD): These domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. Use is based on community theme concepts.
infrastructure top-level domain: This group consists of one domain, the Address and Routing Parameter Area (ARPA). It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in the Request for Comments publications.
Countries are designated in the Domain Name System by their two-letter ISO country code; there are exceptions, however (e.g., .uk). This group of domains is therefore commonly known as country-code top-level domains (ccTLD). Since 2009, countries with non–Latin-based scripts may apply for internationalized country code top-level domain names, which are displayed in end-user applications in their language-native script or alphabet, but use a Punycode-translated ASCII domain name in the Domain Name System.
The Internet’s domain-name system (DNS) allows users to refer to web sites and other resources using easier-to-remember domain names (such as “www.icann.org”) rather than the all-numeric IP addresses (such as “184.108.40.206”) assigned to each computer on the Internet. Each domain name is made up of a series of character strings (called “labels”) separated by dots. The right-most label in a domain name is referred to as its “top-level domain” (TLD).
The DNS forms a tree-like hierarchy. Each TLD includes many second-level domains (such as “icann” in “www.icann.org”); each second-level domain can include a number of third-level domains (“www” in “www.icann.org”), and so on.
The responsibility for operating each TLD (including maintaining a registry of the second-level domains within the TLD) is delegated to a particular organization. These organizations are referred to as “registry operators”, “sponsors”, or simply “delegees.”
There are several types of TLDs within the DNS:
TLDs with two letters (such as .de, .mx, and .jp) have been established for over 250 countries and external territories and are referred to as “country-code” TLDs or “ccTLDs”. They are delegated to designated managers, who operate the ccTLDs according to local policies that are adapted to best meet the economic, cultural, linguistic, and legal circumstances of the country or territory involved. For more details, see the ccTLD web page on the IANA web site.
Most TLDs with three or more characters are referred to as “generic” TLDs, or “gTLDs”. They can be subdivided into two types, “sponsored” TLDs (sTLDs) and “unsponsored TLDs (uTLDs), as described in more detail below.
In addition to gTLDs and ccTLDs, there is one special TLD, .arpa, which is used for technical infrastructure purposes. ICANN administers the .arpa TLD in cooperation with the Internet technical community under the guidance of the Internet Architecture Board.
In the 1980s, seven gTLDs (.com, .edu, .gov, .int, .mil, .net, and .org) were created. Domain names may be registered in three of these (.com, .net, and .org) without restriction; the other four have limited purposes.
In years following the creation of the original gTLDs, various discussions occurred concerning additional gTLDs, leading to the selection in November 2000 of seven new TLDs for introduction. These were introduced in 2001 and 2002. Four of the new TLDs (.biz, .info, .name, and .pro) are unsponsored. The other three new TLDs (.aero, .coop, and .museum) are sponsored. In 2003, ICANN initiated a process that resulted in the introduction of six new TLDs (.asia, .cat, .jobs, .mobi, .tel and .travel) that are sponsored. Information about that process may be found here.
Generally speaking, an unsponsored TLD operates under policies established by the global Internet community directly through the ICANN process, while a sponsored TLD is a specialized TLD that has a sponsor representing the narrower community that is most affected by the TLD. The sponsor thus carries out delegated policy-formulation responsibilities over many matters concerning the TLD.
A Sponsor is an organization to which is delegated some defined ongoing policy-formulation authority regarding the manner in which a particular sponsored TLD is operated. The sponsored TLD has a Charter, which defines the purpose for which the sponsored TLD has been created and will be operated. The Sponsor is responsible for developing policies on the delegated topics so that the TLD is operated for the benefit of a defined group of stakeholders, known as the Sponsored TLD Community, that are most directly interested in the operation of the TLD. The Sponsor also is responsible for selecting the registry operator and to varying degrees for establishing the roles played by registrars and their relationship with the registry operator. The Sponsor must exercise its delegated authority according to fairness standards and in a manner that is representative of the Sponsored TLD Community.
The extent to which policy-formulation responsibilities are appropriately delegated to a Sponsor depends upon the characteristics of the organization that may make such delegation appropriate. These characteristics may include the mechanisms the organization uses to formulate policies, its mission, its guarantees of independence from the registry operator and registrars, who will be permitted to participate in the Sponsor’s policy-development efforts and in what way, and the Sponsor’s degree and type of accountability to the Sponsored TLD Community.
The domain arpa was the first Internet top-level domain. It was intended to be used only temporarily, aiding in the transition of traditional ARPANET host names to the domain name system. However, after it had been used for reverse DNS lookup, it was found impractical to retire it, and is used today exclusively for Internet infrastructure purposes such as in-addr.arpa for IPv4 and ip6.arpa for IPv6 reverse DNS resolution, uri.arpa and urn.arpa for the Dynamic Delegation Discovery System, and e164.arpa for telephone number mapping based on NAPTR DNS records. For historical reasons, arpa is sometimes considered to be a generic top-level domain.
RFC 6761 reserves the following four top-level domain names to avoid confusion and conflict. Any such reserved usage of those TLDs should not occur in production networks that utilize the global domain name system:
example: reserved for use in examples
invalid: reserved for use in obviously invalid domain names
localhost: reserved to avoid conflict with the traditional use of localhost as a hostname
test: reserved for use in tests
In the late 1980s InterNIC created the nato domain for use by NATO. NATO considered none of the then existing TLDs as adequately reflecting their status as an international organization. Soon after this addition, however, InterNIC also created the int TLD for the use by international organizations in general, and persuaded NATO to use the second level domain nato.int instead. The nato TLD, no longer used, was finally removed in July 1996.
Other historical TLDs are cs for Czechoslovakia (now using cz for Czech Republic and sk for Slovak Republic), dd for East Germany (using de after reunification of Germany), yu for SFR Yugoslavia (now using ba for Bosnia and Herzegovina, hr for Croatia, me for Montenegro, mk for Macedonia, rs for Serbia and si for Slovenia), and zr for Zaire (now cd for Democratic Republic of the Congo). In contrast to these, the TLD su has remained active despite the demise of the Soviet Union that it represents.
Around late 2000 when ICANN discussed and finally introduced aero, biz, coop, info, museum, name, and pro TLDs, site owners argued that a similar TLD should be made available for adult and pornographic websites to settle the dispute of obscene content on the Internet and the responsibility of US service providers under the US Communications Decency Act of 1996. Several options were proposed including xxx, sex and adult. The .xxx domain went live in 2011.
An older proposal consisted of seven new gTLDs: arts, firm, info, nom, rec, shop, and web. Later biz, info, museum, and name covered most of these old proposals.
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 gTLDs being registered. Proposed TLDs included free, music, shop, berlin, wien and nyc.
On 13 June 2012 ICANN has revealed nearly 2,000 applications for new top-level domains, which began to go live throughout 2013 after thorough examination. Donuts Inc. has invested $57 million in more than 300 applications whilst Famous Four Media applied for 61 new strings. The first seven – .bike, .clothing, .guru, .holdings, .plumbing, .singles, and .ventures – are already live, and all belong to Donuts. More have been released throughout 2014 and will continue coming online steadily into 2015.