Top Level Domain


The term “top-level domain” (TLD) refers to the last segment of a domain. When editing and referencing a domain name, the domain name system also takes into account the top-level domain. It represents the highest level of a domain. The TLD can provide information about the geographic orientation of a website (ccTLD) as well as the topic-specific (gTLD) affiliation. In many cases, however, top-level domains can also be used independently of the topic and region.

Background[edit]

The top-level domain developed simultaneously with the introduction of the domain name system (DNS). Prior to this, it was common for different computers to communicate over the Internet only with a corresponding IP address. The rewriting of the decimal codes into web addresses was absolutely necessary for a more common practice. In January 1985, the first Domain was registered with nordu.net. The first .com addresses followed in March. In Germany, the first domains were registered in 1988.

In order to be able to better classify the later registrations, the IANA has given out both generic (gTLD) and country-specific domain endings (ccTLD). There are also two infrastructure TLDs with .arpa and .root.

Technical implementation[edit]

The top-level domains are managed by a set of Nameservers. The servers responsible for the respective domain extensions can be reached via root nameservers. All data concerning the domain owner and registration are saved in a central database. This data can usually be obtained with a Whois request.

ICANN commissions separate service providers for each domain ending to administer the servers and database (Domain Name Registry). The DENIC, for example, is responsible for the .de-ending in Germany. The respective domain names are saved by registrars.

In order to register and use a website with a corresponding TLD, certain allocation rules, which are obtainable from the registrars, have to be observed. Thus, it is, for example, not always possible to use umlauts in a domain name.

Generic top-level domains[edit]

Generic top-level domains are usually allocated to organizations and companies. Two different groups are distinguished:

[edit]

These domain endings are under the control of independent organizations or government organizations and are also financed by them. The rules for their allocation are drawn up by these organizations as well.

  • .aero – for aerospace companies or companies active in the sector
  • .asia – originally intended for individuals and companies of the Asia-Pacific region and Australia, the ending has been available for anyone since 2007.
  • .cat – specifically designed for websites that address the Catalan language and culture
  • .coop – TLD reserved for cooperatives
  • .edu – for educational institutions accredited by the competent US authority
  • .gov – for US government websites
  • .int – for domains of multinational organizations
  • .jobs – reserved for companies that present job offers
  • .mil – for US military sites
  • .mobi – for domains specifically designed for mobile devices such as tablets or smartphones
  • .museum – for home pages of museums
  • .post – for logistics companies and postal services
  • .tel – designed for the standardized backup of contact data and their publication
  • .travel - reserved for the tourism industry, e.g. Airlines
  • .xxx – for websites with erotic content

Non-sponsored TLD (uTLD)[edit]

These domains are distributed and controlled by ICANN and the Internet Society. They refer to groups and organizations.

  • .arpa – Infrastructure domain
  • .biz – originally intended for commercial offerings on the web, now usable for everyone
  • .com – actually only planned for US companies, today can be registered for anyone
  • .info – originally designed for information pages, today freely accessible to all
  • .name – for natural persons, but reserved for all
  • .net – initially reserved for companies dealing with the administration of the Internet, today a freely accessible uTLD
  • .org –once explicitly reserved for non-profit organizations, but now usable by everyone, including commercial providers
  • .pro – Special TLD for certified specialists

Over time, the purpose of many non-sponsored TLD has softened. Today, domains can no longer be identified by these extensions.

Country code top-level domains[edit]

The country codes are defined according to ISO-3166. There are more than 200 ccTLDs (country-specific top-level domains) in total. Each country is assigned a two-digit country code. In addition, individual independent regions may receive their own TLD.

Exceptions to this rule are the country code .uk for domains from the United Kingdom as well as .eu, for websites originating from the EU. The introduction of subdomains for the .eu ending is planned. As soon as states change, new ccTLDs are created. An example of this is the former abbreviation .zr for Zaire. Because the country is now called the Democratic Republic of the Congo, it now has the country code .cd.

The rules for the allocation of country-specific domain endings are defined by each country itself. For a large part of the ccTLD, it is necessary that the corresponding website is operated by a company working in the country concerned or a person living in that country. This is the case, for example, with the top-level domain of France (.fr).

In Germany, the rule was that a domain needed to have more than two digits before the ending. This is now outdated. In England, only specific third-level domain names are allowed for a second name level, e.g. co.uk for commercial websites.

ccTLD exceptions[edit]

Interesting exceptions in the allocation of country-specific TLDs are the endings of Tonga .to and Colombia .co. Both countries have allowed their use regardless of the place of residence. Especially the .to websites are often related to gaming and Torrent sites, since the respective domains can be registered anonymously.

The domain ending of the Federated States of Micronesia, .fm, is mostly used for radio web sites. The same is true for the ccTLD .im of the Isle of Man, which is utilized for Instant Messenger and the top-level domain of Tuvalu, .tv gets used for TV broadcasts or websites. In addition to these known examples, there are other country-specific TLDs which are also used to make reference to specific regions, such as .be (Belgium), also being used for the canton of Bern in Switzerland.

New top level domains[edit]

Over the years, ICANN has recognized that new sponsored domain extensions are needed and in 2008 the requirements for applicants were relaxed. The application procedure was finally implemented in 2012. New domain endings are now being approved regularly. For example, .berlin was approved for Berlin, Germany in 2014.

Web Links[edit]