Top-level domain
From Wikipedia, the free encyclopedia
A top-level domain or domain name (TLD) is the highest level of domain names in the root zone of the Domain Name System of the Internet. For all domains in lower levels, it is the last part of the domain name, that is, the label that follows the last dot of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com (or COM, as domain names are not case-sensitive). Management of most top-level domains is delegated to responsible 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.
Originally, the top-level domain space was organized into three main groups,[1] Countries, Categories, and Multiorganizations. An additional temporary group consisted only of the initial DNS domain,[2] arpa, intended for transitional purposes toward the stabilization of the domain name system.
Countries are designated in the domain name system by their English two-letter ISO country code[3]. This group of domains is therefore commonly known as country-code top-level domains (ccTLD).
The Categories group has become known as the generic top-level domains. Initially this group consisted of GOV, EDU, COM, MIL, ORG, and NET.
In the growth of the Internet, it became desirable to create additional generic top-level domains. Some of the initial domains' purposes were also generalized, modified, or assigned for maintanance to special organizations affiliated with the intended purpose.
As a result, IANA today distinguishes the following groups of top-level domains:[4]
- country-code top-level domains (ccTLD): Used by a country or a dependent territory. It is two letters long, for example .us for the United States. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
- generic top-level domains (gTLD): Generic domains are essentially open for registration to anyone in the world.
- generic-restricted top-level domains: Similar to general generic group, except eligibility is supposed to be restricted and ascertained more stringently.
- 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. Often they are also grouped with the generic top-level domains.
- infrastructure top-level domain: This group consists of one TLD, the Address and Routing Parameter Area (ARPA). It is managed by IANA on behalf of the IETF for various purposes specified in RFCs.
In addition, a group of internationalized domain name (IDN) top-level domains has been installed under test for testing purposes.
The authoritative list of currently existing TLDs in the root zone is published at the IANA website at http://www.iana.org/domains/root/db/ and a Wikipedia list exists.
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[edit] Infrastructure domain
The domain arpa was the first Internet top-level domain. It was intended to be only temporary, 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 be retired, 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 these historical reasons, arpa is sometimes considered to be a generic TLD.
[edit] Reserved domains
RFC 2606 reserves the following four top-level domain names to avoid confusion and conflict.[5] They may be used for various specific purposes however, with the intention that these should not occur in production networks within 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
The test domain has seen usage by ICANN in the testing of internationalized domain names, a program started in 2007.[6][7]
- xn--kgbechtv Arabic (إختبار)
- xn--hgbk6aj7f53bba Persian (آزمایشی)
- xn--0zwm56d Chinese, simplified (测试)
- xn--g6w251d Chinese, traditional (測試)
- xn--80akhbyknj4f Cyrillic (испытание)
- xn--11b5bs3a9aj6g Hindi (परीक्षा)
- xn--jxalpdlp Greek (δοκιμή)
- xn--9t4b11yi5a Korean (테스트)
- xn--deba0ad Yiddish (טעסט)
- xn--zckzah Japanese (テスト)
- xn--hlcj6aya9esc7a Tamil (பரிட்சை)
[edit] Historical domains
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 cz for Czech Republic and sk for Slovak Republic), dd for East Germany (using de after reunification of Germany), 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.
[edit] Proposed domains
About the time that ICANN discussed and finally introduced[8] aero, biz, coop, info, museum, name, and pro TLDs, site owners and USENET users 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 service providers under the questionable Communications Decency Act of 1996. Several options were proposed including xxx, sex and adult, but ICANN has not created any.[9]
An older proposal[10] 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,[11] 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 a new application and implementation process.[12] Observers believed that the new rules could result in hundreds of new gTLDs to be registered.[13] Proposed TLDs include music, berlin and nyc.
[edit] Pseudo-domains
In the past the Internet was just one of many wide-area computer networks. Computers not connected to the Internet, but connected to another network such as BITNET, CSNET or UUCP, could generally exchange e-mail with the Internet via e-mail gateways. For relaying purposes on the gateways, messages associated with these networks were labeled with suffixes such as bitnet, oz, csnet, and uucp, but these domains did not exist in the public domain name system.
Most of these networks have long since ceased to exist, and although UUCP still gets significant use in parts of the world where Internet infrastructure has not yet become well-established, it subsequently transitioned to using Internet domain names, so pseudo-domains now largely survive as historical relics. One notable exception is the 2007 emergence of SWIFTNet Mail, which uses the swift pseudo-domain.[14]
local deserves special mention as it is required by the Zeroconf protocol. It is also used by many organizations internally, which will become a problem for those users as Zeroconf becomes more popular. Both site and internal have been suggested for private usage, but no consensus has emerged[citation needed].
[edit] TLDs in alternative roots
ICANN's slow progress in creating new gTLDs, and the high registration costs associated with TLDs, contributed to the creation of alternate root servers with their own sets of TLDs. At times, browser plugins have been developed to allow access to some set of "alternative" domain names even when the normal DNS roots are otherwise used.
The anonymity network Tor has a pseudo-domain onion, which can only be reached with a Tor client because it uses the Tor-protocol (onion routing) to reach the hidden service in order to protect the anonymity of the domain.
[edit] See also
[edit] References
- ^ RFC 920, Domain Requirements, J. Postel, J. Reynolds, The Internet Society (October 1984)
- ^ RFC 921, Domain Name System Implementation Schedule - Revised, J. Postel, The Internet Society (October 1984)
- ^ Codes for the Representation of Names of Countries, ISO-3166, International Standards Organization (May 1981)
- ^ IANA root zone database
- ^ RFC 2606 (BCP 32), Reserved Top Level DNS Names, D. Eastlake, A. Panitz, The Internet Society (June 1999)
- ^ ICANN IDN wiki
- ^ IANA (ICANN) list of extant TLDs
- ^ InterNIC FAQs on New Top-Level Domains
- ^ RFC 3675: sex Considered Dangerous
- ^ (historical) gTLD MoU
- ^ "32nd International Public ICANN Meeting". ICANN. 2008-06-22. http://par.icann.org/.
- ^ "New gTLS Program". ICANN. http://www.icann.org/en/topics/new-gtld-program.htm. Retrieved on 2009-06-15.
- ^ ICANN Board Approves Sweeping Overhaul of Top-level Domains, CircleID, 26 June 2008.
- ^ SWIFT - About SWIFT - Press room - SWIFTNet Mail now available
- Addressing the World: National Identity and Internet Country Code Domains, edited by Erica Schlesinger Wass (Rowman & Littlefield, 2003, ISBN 0-7425-2810-3) [1], examines connections between cultures and their ccTLDs.
- Ruling the Root by Milton Mueller (MIT Press, 2001, ISBN 0-262-13412-8) [2], discusses TLDs and domain name policy more generally.
- RFC 1591 - Domain Name System Structure and Delegation
- RFC 3071 - Reflections on the DNS, RFC 1591, and Categories of Domains
[edit] External links
- Articles on CircleID about TLDs
- IANA TLD List
- "Top-Level Domain Names by Host Count". ISC. January 2008. http://ftp.isc.org/www/survey/reports/current/report.bynum. Retrieved on 2008-08-07.
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