Top-level domain (English for "top level area", abbreviation TLD ) describes the last section (to the right of the point) of a domain in the Internet and represents the highest level of name resolution . Is the complete domain name of a server or website for example www.example.com , the letter combination .com on the far right corresponds to the top-level domain of this name.
In the Domain Name System (DNS) the names and thus also the TLDs are referenced and resolved, i.e. assigned to a unique IP address . As part of the domain registration , the domain name registrar creates a database entry about the owner, which enables Whois queries via the protocol of the same name, similar to a telephone book .
The IANA divides TLDs into two main groups and one special case (as of 2019)
Country-specific TLDs :
- country code TLD s ( ccTLD s)
- Internationalized country-specific top-level domains - Internationalized Domain Name country-code TLD ( IDN ccTLD )
- general TLDs: generic TLD s ( gTLD s),
- sponsored TLD s ( sTLD s) and unsponsored TLD s ( uTLD s)
- internationalized top-level domains
- the infrastructure TLD ( iTLD ) .arpa (special case) and the (but never used) .root
The special cases .bitnet and .uucp are no longer in use .
A list of all top-level domains can be found on the IANA website, see section Weblinks “Root Zone Database”.
Generic top-level domains
The generic top-level domains (gTLD) are divided into sponsored (sTLD) and non-sponsored (uTLD). The (much more important) unsponsored domains are under the direct control of ICANN and the Internet Society . The sponsored domains are controlled and financed by independent organizations. These organizations have the right to apply their own guidelines for assigning domain names. One example is .mil. This domain is used exclusively by the US military.
By far the most widely used TLD is .com (approx. 127 million registered domains in September 2017). Originally used by US companies, it is now used around the world.
Unsupported domains (uTLD)
Non-sponsored top-level domains ( English unsponsored top-level domain , abbreviation uTLD ) are used by a certain group. They consist of three or more characters and stand for a term that distinguishes this group.
|.arpa||arpanet||TLD of the original Arpanet , now used as the Address and Routing Parameter Area . The IANA calls this TLD the "infrastructure domain".||Yes|
|.biz||business||for commercial use only; de facto freely accessible to everyone. Designated generic-restricted by the IANA .||Yes|
|.com||commercial||originally only for companies , for a long time freely accessible to everyone||Yes|
|.info||information||intended for information providers , but freely accessible to everyone from the start.||Yes|
|.Surname||Surname||only for natural persons or families (private individuals); de facto freely accessible to everyone. Designated generic-restricted by the IANA .||No|
|.net||network||originally for network management institutions, today free for everyone.||Yes|
|.org||organization||for non-commercial organizations ( non-profit organizations ), free for everyone since 2003.||Yes|
|.Per||professionals||for “qualified specialists ” (a few professional groups) who identify themselves as such by means of “suitable certificates”. Designated generic-restricted by the IANA .||No.|
Due to the liberal allocation for the TLDs .com , .net , .org and (with minor restrictions) .biz and (more recently) .name , the original meanings of these TLDs have largely been lost. Such a TLD does not necessarily indicate a corresponding use. For example, the .org TLD, which was actually intended for non-commercial organizations, is now occasionally used by commercial providers. Furthermore, international, non-commercial websites like to use .net (or .org) so that they do not have to fall back on a country-specific TLD or the widespread .com. While .org is now only listed as a generic TLD by the IANA , the TLDs biz , .name and .pro are still classified as generic-restricted for the time being (as of August 2019) .
Sponsored Domains (sTLD)
Sponsored domains ( sponsored top-level domains , abbreviation sTLD ) are proposed by certain companies or organizations that operate these namespaces in accordance with detailed guidelines and also have control and sanction rights with which the intended and lawful use of the registered names is carried out the provider should be ensured. For example, the TLD .aero is sponsored by SITA , which restricts use to aviation content, or the use of .mobi names is tied to the website provider ensuring compliance with certain guidelines for the device-independent use of web content be considered elementary, so that z. B. mobile phones can display this content.
|Existing sponsored domains|
|.aero||aeronautics||organizations active in the aviation industry||Société Internationale de Télécommunications Aéronautiques||No|
|.asia||asia||Individuals and companies located within ICANN's Asia / Australia / Pacific region (accessible to everyone since October 2007)||Yes|
|.cat||catalan||Catalan language and culture||Fundació puntCAT||Yes|
|.coop||cooperatives||Cooperatives||Dot Cooperation LLC||No|
|.edu||educational||since 2001 limited to educational institutions accredited by a United States Department of Education accredited accreditation agency. Apart from a few institutions that already had a .edu domain and grandfathering enjoy are, this almost exclusively US colleges and universities.||Yes|
|.gov||government||US government bodies only||Yes|
|.jobs||jobs||only companies with vacancies||No|
|.lgbt||LGBT *||LGBT * community|
|.mil||military||US military facilities only||Yes|
|.mobi||mobile||to identify services that explicitly support use by mobile devices||mTLD Top Level Domain Limited||No|
|.museum||museum||Museums||Museum Domain Management Association||Yes|
|.post Office||postal||Post and logistics company||Universal Postal Union||Yes|
|.tel||telecommunication||standardized storage and publication of contact data; Saves data directly in the Domain Name System as NAPTR and TXT record||No|
|.travel||travel||Travel industry (e.g. travel agencies, airlines, etc.)||No|
|.xxx||sex||erotic and sexual content||ICM registry||No|
On June 26, 2008, ICANN decided to relax the rules for new sponsored domains. In the following months, rules and the application process were developed. On June 20, 2011, ICANN passed an application process for new generic top-level domains (gTLD) in Singapore. Between January 12, 2012 and May 30, 2012, interested parties could apply for a new TLD. On June 13, 2012, the so-called Reveal Day , ICANN published a list of which applicants had submitted applications for which new desired top level domains. In a period of about two years, ICANN wants to examine the proposals and decide on any approvals. Approved and used top-level domains of this new type are for example .berlin , .koeln and .swiss .
|.arpa||Today the domain is used as an infrastructure domain for technical purposes in the DNS and some other tasks and is administered by the IANA . It was originally only intended to be a temporary solution for setting up the DNS on the Internet, but the later resolution of this domain turned out to be impractical. The in-addr.arpa subdomain is used worldwide to enable the resolution of an IPv4 address into a domain name ( reverse lookup ), with IPv6 ip6.arpa is used for the same purpose. Another subdomain, e164.arpa, is used for ENUM , the addressing of Internet services via telephone numbers (keyword Voice-over-IP ).||Yes|
|.bit||.bit is a pseudo top level domain of the Namecoin project. It is not approved by ICANN and is therefore not part of the corresponding official DNS.||-|
|.bitnet||The domain was used in the early days of the Internet when some technically different networks were operated side by side. It was an IBM- sponsored branch of the network to demonstrate feasibility; the name means b ecause i t’s t ime - net .||-|
|.example||According to RFC 2606 , this domain is reserved for examples in texts, documentation and the like. It is not assigned, as are the second-level domains example.com , example.net , example.org . For example, automatically generated links in online documents do not refer to real domains.||-|
|.invalid||This domain is reserved by RFC 2606 as an example of a guaranteed non-existent domain. It can be used for software tests, for example .||-|
|.local||This domain is used in Multicast DNS for link-local addresses.||-|
|.localhost||localhost is used locally on most computers for their loopback device . Therefore, according to RFC 2606, it is not assigned elsewhere, since it would generally not be accessible anyway.||-|
|.nato||.nato originally existed for NATO , but was given up after the .nato.int domain was registered for it.||-|
|.onion||.onion is a special-use top-level domain for the use of hidden services (German: hidden services) in the anonymization service The Onion Routing (Tor). The .onion addresses are not part of the DNS, but can be interpreted by applications if they are sent through a proxy into the Tor network.||-|
|.root||The domain "vrsn-end-of-zone-marker-dummy-record.root" existed in the root zone until DNSSEC was introduced . The purpose of its existence was a simple test whether the root zone was completely transferred during a zone transfer, which was possible since the domain was the last entry in the zone.||-|
|.test||According to RFC 2606 , this domain is reserved for tests and is not officially assigned, but can be used locally.||-|
|.uucp||For a long time, this domain was a pseudo-domain in TCP / IP networks for computers in the uucp mapping project that did not have their own internet domain or acted as gateways . As a rule, these computers could only be reached via telephone modem connections or only passively.||-|
Country-specific top-level domains (ccTLD)
There are over 200 ccTLDs (cc = country code), each country is assigned exactly one two-letter code (ALPHA-2) according to ISO 3166 . In addition, there are often separate ccTLDs for dependent areas, which are mostly geographically separated from the mother country.
- The UK uses the TLD .uk , although the ISO encoding is GB (GB, GBR, 826). In addition, the ISO also reserved the UK coding as an exception. The .gb TLD is also reserved, but is currently not used, apart from a single registration.
- The European Union used with .eu a ccTLD, although it is not an independent state. The coding EU was exceptionally reserved with this meaning by the ISO 3166 Maintenance Agency. This was done through a special decision based on an established practical need. In contrast to states, the EU has neither a three-letter nor a three-digit coding. Its member countries will continue to keep their own ccTLDs, and no country-specific subdomains of .eu will be introduced.
- .dd was intended for the GDR , but was only used internally at the universities in Jena and Dresden . There was no DNS delegation in the IANA's root name servers , the top-level domain .dd was replaced by .de of the Federal Republic of Germany after reunification .
- .cs was previously used for Czechoslovakia . This TLD was later intended for the now dissolved state union of Serbia and Montenegro . Due to name conflicts with the websites and e-mail addresses of the former Czechoslovakia that still exist , this was apparently not implemented on the servers. Instead, .yu continued to be used for Serbia and Montenegro . With the breakup into the individual states and their domains .rs and .me , the matter was settled. .Cs will no longer be required in the future . The abbreviations used after the separation of Czechoslovakia are .cz for the Czech Republic and .sk for Slovakia.
- .zr for Zaire was removed from the root servers in 2004 (now .cd ).
- .um for the United States Minor Outlying Islands was assigned to the registrar and operator University of Southern California Information Sciences Institute but was never used. Therefore, in consultation with ICANN , the United States Department of Commerce - National Telecommunications and Information Administration (NTIA) and the operator, the .um domain was reset to an unused status in 2008. It was agreed that ICANN should not take any action with regard to the future use of the .um domain without consulting the US government and obtaining its prior consent . Since then, .um has been listed by the IANA in the Root Zone Database as "Not assigned" until today (2019).
- .yu for Yugoslavia was dissolved on September 30, 2009 (no longer available since March 30, 2010), as it was replaced by the two domain extensions .rs for Serbia and .me for Montenegro .
- .an for the Netherlands Antilles was permanently deleted on July 31, 2015 due to its dissolution in 2010. Was replaced .an by the inclusion of top-level domains .bq (for the special municipalities of the Netherlands has become three "islands" Bonaire , Sint Eustatius and Saba ) as .cw for Curacao and .sx for Sint Maarten (both Caribbean islands now autonomous countries within the Kingdom of the Netherlands), in the root zone by ICANN on December 20, 2010.
Some obsolete TLDs are still active for reasons of availability:
- In Russia , in addition to .ru , .su (former Soviet Union ) is also operated. Even after the dissolution of the Soviet Union, new domains are registered under .su. This also includes presences from the German Rhein-Sieg district ( license plate SU).
- East Timor switched from .tp to .tl and operated both TLDs for a transitional period until 2015.
Allocated but unused are currently:
Not yet assigned
The following ccTLDs have not yet been assigned:
Conditions of allocation
Every country has the right to set its own allocation guidelines for its domain. The vast majority of these are set up independently by the awarding authorities due to technical necessities and legal requirements and can differ considerably from one another.
For example, in order to register under the French TLD .fr, proof of residence or company headquarters in France (since December 6, 2011 in the European Union) had to be proven.
In Germany , on October 23, 2009, the allocation of one-, two-digit and only digit domains with .de began. Until then, the .de domain had to consist of at least three characters, and one of them had to be a letter. From the early days of the Internet there were three two-digit domains: db.de , hq.de and ix.de . (The fourth two-letter domain bb.de for a long time was no longer registered at the time of the settlement.) Volkswagen sued the Higher Regional Court in Frankfurt am Main for the allocation of the domain vw.de , which then went into operation on the key date has been.
In Switzerland , only the cantons have a domain with two characters resulting from the official abbreviation (e.g. ar.ch , ge.ch , ur.ch , zh.ch ). The ch.ch domain is also operated by the Federal Chancellery . Apart from these exceptions, Swiss domains must consist of at least three characters. Exceptions are www.expo.02.ch (for the sixth Swiss National Exhibition 2002 ) and the au.ch domain of the municipality of Au in the canton of St. Gallen .
In other cases, only a few predefined names are possible for the second name level; the actual name is then defined as a third-level domain (e.g. example.co.uk ). One example was the British .uk domain, which only allowed the following second-level domains until June 9, 2014:
- .ac.uk - academic , educational institutions such as universities
- .co.uk - commercial
- .gov.uk - government , central and regional government organizations
- .ltd.uk - limited company
- .me.uk - presences of individuals
- .net.uk - ISPs and other network companies
- .nhs.uk - National Health Service , state health system and its institutions
- .nic.uk - Network Information Center , for internal network administration only
- .org.uk - non-profit organizations
- .plc.uk - public limited companies (listed companies)
- .sch.uk - schools
In addition, there are some state-used second-level domains such as .police.uk , .mod.uk ( Ministry of Defense ), .british-library.uk (and .bl.uk - also for the British Library ) or .parliament.uk . These come from an earlier time and are grandfathered.
Smaller states or countries affected by poverty, in particular, market their domains by handling their allocation policy very liberally and actively promoting the registration of domains. The domain market is developing into a lucrative business, as the registration fees are sometimes set significantly above the actual costs.
The domain of Colombia is also used instead of the ending .com, for example with the meaning "Company", "Commerce", "Corporation", "Community", "Content", "Connection".
One of the first such states to have their domains freely registered was Tonga with .to in 1998 . The response was very good, because at that time a lot of short and concise domains under .com were no longer available, and other ccTLDs sometimes had very strict registration requirements. In addition resulted from the ending .to interesting domain names well in short URLs could be used as come.to or go.to . Today the TLD .to is happy to torrent or warez sites used, among other reasons, also because the NIC does not allow holders queries so that they can be anonymous domains registered.
The .fm TLD of the Federated States of Micronesia is widely used in broadcasting. The abbreviation FM stands for frequency modulation in radio broadcasting , which is used in VHF broadcasting and is usually associated with it.
The association of an abbreviation is also used, for example, by the websites of some instant messaging services ( IM for short ) whose TLD .im is registered on the Isle of Man , e.g. B. in the instant messenger Pidgin ( pidgin.im ).
Another well-known third-party ccTLD is .tv from the state of Tuvalu , which is marketed as television . For this purpose, a separate company DotTV was founded, which markets the domain and in which the state of Tuvalu is a co-owner. This coup brought the tiny country of 50 million dollars that will be paid in annual installments of $ 5 million. Tuvalu is even honoring the domain sale with its own stamp. Tuvalu's government used the money to procure IT infrastructure for the most important government institutions and paid the entry fee for the United Nations .
Countries or the companies that market their TLDs are also trying to create a market by using abbreviations that are intended to put the address in a context that was not originally given. One company is marketing the .la ( Laos ) domain as a domain for Los Angeles .
- Federal states
- Counties and independent cities
The following list is only to be understood as a selection.
In Switzerland, where the cantons are always abbreviated with two letters, ccTLDs are sometimes used to market offers relating to a canton. For example:
.ag ( Antigua and Barbuda ): The ccTLD of this island state is advertised by the operator in addition to its intended use specifically for companies in German-speaking countries in order to clarify their legal form of a stock corporation (AG).
TLDs are listed here that have no meaning as an abbreviation (like all of the above), but are used for other reasons.
.me ( Montenegro ): It can be used to create meaningful domains, such as. B .: love.me , contact.me etc. However, such domains cannot be registered by the interested party, but are auctioned after the open registration.
.nu ( Niue ): The use of this domain for the pages of the Dresden culture magazine , whichalludes to the nu for "yes" usedin the local Dresden region,is unusual. The domain has a similar meaning in Sweden , Denmark and the Netherlands , since nu means "now"in Swedish , Danish and Dutch , as well as in many English-speaking countries where it is a non-spelling variant of new "new". In addition, .se domains (Sweden) were previously not registered there for private individuals. French-language adult sites like to use this ending, as the word nu translates as naked .
.cc ( coconut islands ): is very popular because it can be registered by anyone and the whois system is minimalist. (Only the domain registrar is disclosed, which means that the domain operator remains virtually anonymous.)
In addition to the domains mentioned here, there are a large number of domains with imaginative names such as .creditcard .futbol and much more. More than 600 domains are listed in the picture. Which of these possible domains will actually be used is questionable.
Technical and administrative implementation
For each top-level domain there is a group of name servers that manage the entire namespace of this domain (usually by means of delegations to other servers). These domain-specific name servers can be reached via the root name servers. There is also a central database that contains administrative information on all second-level domains located below this TLD, such as the name and address of the respective domain owner. This database can be accessed via the Whois service.
For the operation of the server and the database, ICANN commissions an organization for each domain, which is called the Domain Name Registry in Internet terminology . For the .com TLD, for example, this is VeriSign , for .de, DENIC . Such a registry is also responsible for assigning directly subordinate second-level domains (e.g. example.com ). However, this task is often delegated to so-called registrars (see also: Domain registration ).
For every TLD there are guidelines that regulate the allocation of second-level domains. These are available on the websites of the respective registries. For some TLDs there are IDN language tables in which all special characters are listed that may be used when assigning subdomains. For example, German umlauts are permitted for .biz and .org. These tables are administered by IANA and can be viewed on the registries' websites.
Alternative root DNS
There are also organizations on the Internet that operate alternative name servers through which further TLDs are available in addition to the quasi-official TLDs controlled by ICANN . A decisive disadvantage is that such addresses cannot be reached by conventional Internet users. They are also ignored by search engines like Google . Another disadvantage is that the namespaces of two operators can collide, especially if further top level domains are introduced later.
The OpenNIC project tries to merge the alternative systems, but regards the ICANN TLDs as priority and accepts neither conflicting nor private namespaces. The own TLDs are .glue , .indy , .geek , .null , .oss and .parody .
In the second quarter of 2018, the total number of registered domains was over 329 million.
The most frequently registered TLDs worldwide (as of October 2018):
|.cn||CNNIC||10,890,519||People's Republic of China|
|.ru||CC for TLD RU||4,921,743||Russia|
|.ga||RIPE Network Coordination Center||2,353,985||Gabon|
|.biz||neustar Domain Registry||2.250.208|
|.cf||SOCATEL||2,238,368||Central African Republic|
TLDs from states with German as the official language:
- For the local rules of the TLDs (residence, mandatory second level domain etc.) there is a list of links in the English language Wikipedia
- RFC 2606 - Top-Level Reserved DNS Names
- Root Zone Database - official list of all top-level domains on the IANA website (English)
- List of all ccTLD-compliant German vehicle district numbers
- Hurricane Electric's detailed TLD listing
- How to work around problems with the new top-level domains from Digital Guide
- DENIC eG: Domainmarkt International
- Statista - Evaluations Domains Q1 2017 Accessed on February 27, 2013.
- Terry Manderson (ICANN): TLD DNSSEC Report , November 11, 2012. Accessed November 11, 2012.
- ICANN - Archives - ICANN Montreal Meeting Topic: Review of ICANN's Geographic Regions. In: icann.org. July 15, 2000, accessed March 5, 2020 .
- Home - dotMobi. Internet made mobile. Everywhere, every device. In: mtld.mobi. Retrieved March 2, 2015 .
- ICM Registry - .XXX Sponsored Top Level Domain. (No longer available online.) In: registry.xxx. Archived from the original on December 31, 2016 ; accessed on March 2, 2015 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- Monika Ermert: Green light for new Internet address zones - heise online. In: heise.de. June 26, 2008, accessed March 2, 2015 .
- Florian Hitzelberger: nTLDs - June 13, 2012 is »reveal day«! In: domain-recht.de. June 13, 2012, accessed March 2, 2015 .
- Reveal Day 13 June 2012 - New gTLD Applied-For Strings ( Memento from June 15, 2012 in the Internet Archive ), ICANN. Retrieved June 14, 2012.
- Multicast DNS. In: IETF . February 2012, accessed March 5, 2020 .
- IANA ccTLD database on Internet Assigned Numbers Authority. In: iana.org. Retrieved March 2, 2015 .
- ISO 3161 FAQ: What is the ISO 3166-1 code for the European Union? http://www.iso.org/iso/country_codes/iso_3166-faqs/iso_3166_faqs_specific.htm ( Memento from June 6, 2011 in the Internet Archive )
- Robert Scheck - Internet - Top-Level-Domain .DD. In: internet.robert-scheck.de. Retrieved March 2, 2015 .
- IAB to ICANN: IAB input related to the .cs code in ISO 3166, September 24, 2003 - Internet Architecture Board. In: iab.org. December 16, 2011, accessed March 5, 2020 .
- IANA - Report on the Revocation of the .UM Top-Level Domain. In: iana.org. January 16, 2007, accessed March 5, 2020 .
- Rts, Radio Televizija Srbije, Radio Television O: Збогом yu домену. In: rts.rs. March 1, 2015, accessed March 2, 2015 (ci).
- Internet extension .AN as of July 31st uit de lucht - Versgeperst.com Curacao. In: Versgeperst.com Curacao. July 7, 2015, accessed March 13, 2016 (Dutch).
- Florian Hitzelberger: IANA - three new ccTLDs born! In: domain-right. January 25, 2011, accessed March 13, 2016 .
- Domain names registration in SU. In: nic.ru. Retrieved March 2, 2015 .
- 6 Déc 2011 - Overture to l'Europe du .fr et des autres TLDs opérés par l'AFNIC. Retrieved February 6, 2019 (French).
- Allocation of one- and two-digit domains as well as domains consisting only of digits on denic.de
- Marc Störing: Court: Denic has to assign domain with two letters. In: heise.de. June 18, 2008, accessed March 2, 2015 .
- Nominet : Introducing Second Level Domain Names . Retrieved January 25, 2015.
- guidelines (Spanish) ( Memento from September 23, 2015 in the Internet Archive ) (PDF; 76 kB)
- complete listing of the correspondence between TLD and German license plates can be found on the private website www.redirect301.de .
- for example www.uni.kn for the University of Konstanz .
- for example www.messe.la for the “Landshuter Messe- u. Event GmbH ".
- .as is used very often by private individuals, companies, authorities and city administrations. Official websites of various municipalities can only be reached via a TLD that is not intended for use. Due to the small population of American Samoa in relation to Asturias, the majority of the owners of a domain with this extension come from Spain.
- Judgment of the OLG Hamburg on the use of the TLD .ag in Germany
- THE DOMAIN NAME INDUSTRY BRIEF. (PDF) August 2018, accessed on October 8, 2018 .
- Domain Count Statistics for TLDs. Retrieved October 8, 2018 .