Top-level domain#Infrastructure domain

Originally, the top-level domain space was organized into three main groups: Countries, Categories, and Multiorganizations.{{cite journal |title=Domain Requirements |last1=Postel |first1=J. |last2=Reynolds |first2=J. |website=Request for Comments |publisher=Network Working Group | doi=10.17487/RFC0920 |doi-access=free |date=October 1984 |url=https://datatracker.ietf.org/doc/html/rfc920 |access-date=7 February 2011}} An additional temporary group consisted of only the initial DNS domain, .arpa,{{cite journal |title=Domain Name System Implementation Schedule - Revised |last=Postel |first=J. |website=Request for Comments |publisher=Network Working Group |doi=10.17487/RFC0921 |date=October 1984 |url=https://datatracker.ietf.org/doc/html/rfc921 |access-date=7 February 2011 |quote=This memo is a policy statement on the implementation of the Domain Style Naming System in the Internet. This memo is an update of RFC-881, and RFC-897. This is an official policy statement of the IAB and the DARPA.}} and was intended for transitional purposes toward the stabilization of the domain name system.

{{As of|2015|post=,}} IANA distinguishes the following groups of top-level domains:{{cite web |title=IANA root zone database |website=IANA.org |publisher=Internet Assigned Numbers Authority |url=https://www.iana.org/domains/root/db/ |access-date=2015-11-10}}

• Infrastructure top-level domain (ARPA): This group consists of one domain, the Address and Routing Parameter Area. It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in the Request for Comments publications.
• Generic top-level domains (gTLD): Top-level domains with three or more characters
• Generic restricted top-level domains (grTLD): These domains are managed under official ICANN-accredited registrars.
• 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; these domains are managed under official ICANN accredited registrars.
• 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, Cyrillic, Greek, Hebrew, or Chinese).
• Test top-level domains (tTLD): These domains were installed under .test for testing purposes in the IDN development process; these domains are not present in the root zone.

Countries are designated in the Domain Name System by their two-letter ISO country code;Codes for the Representation of Names of Countries, ISO-3166, International Organization for Standardization. (May 1981) 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.

Generic top-level domains (formerly categories) initially consisted of .gov, .edu, .com, .mil, .org, and .net. More generic TLDs have been added, such as .info.

The authoritative list of current TLDs in the root zone is published at the IANA website at [https://www.iana.org/domains/root/db/ https://www.iana.org/domains/root/db/].

An internationalized country code top-level domain (IDN ccTLD) is a top-level domain with a specially encoded domain name that is displayed in an end-user application, such as a web browser, in its language-native script or alphabet (such as the Arabic alphabet), or a non-alphabetic writing system (such as Chinese characters). IDN ccTLDs are an application of the internationalized domain name (IDN) system to top-level Internet domains assigned to countries, or independent geographic regions.

ICANN started to accept applications for IDN ccTLDs in November 2009,{{cite press release |title=ICANN Bringing the Languages of the World to the Global Internet |publisher=Internet Corporation For Assigned Names and Numbers (ICANN) |date=30 October 2009 |url=https://www.icann.org/en/announcements/details/icann-bringing-the-languages-of-the-world-to-the-global-internet--fast-track-process-for-internationalized-domain-names-launches-nov-16-30-10-2009-en |access-date=30 October 2009}} and installed the first set into the Domain Names System in May 2010. The first set was a group of Arabic names for the countries of Egypt, Saudi Arabia, and the United Arab Emirates. By May 2010, 21 countries had submitted applications to ICANN, representing 11 scripts.{{cite news |title='Historic' day as first non-Latin web addresses go live |work=BBC News |date=6 May 2010 |url=https://www.bbc.com/news/10100108 |access-date=7 May 2010}}

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.{{Cite web |title=.ARPA Domain |url=https://www.iana.org/domains/arpa |access-date=2023-12-16 |website=www.iana.org}}

A set of domain names is reserved{{cite web |title=IANA-managed Reserved Domains |publisher=IANA |url=https://www.iana.org/domains/reserved |access-date=4 March 2022}}{{cite web |title=Special-Use Domain Names |publisher=IANA |url=https://www.iana.org/assignments/special-use-domain-names/special-use-domain-names.xhtml |access-date=3 March 2022}} by the Internet Engineering Task Force as special-use domain names. The practice originated in RFC 1597 for reserved address allocations in 1994 and reserved top-level domains in RFC 2606 of 1999, with additional reservations in later RFCs. These reserved names should not be used in production networks that utilize the global domain name system.

{{More citations needed|section|date=December 2018}}

In the late 1980s, InterNIC created the .nato domain for use by NATO.{{citation needed|date=November 2020}} 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.{{citation needed|date=November 2020}}

Other historical TLDs are .cs for Czechoslovakia (now using .cz for Czech Republic and .sk for Slovakia), .dd for East Germany (using .de after reunification of Germany), .yu for SFR Yugoslavia and Serbia and Montenegro (now using .ba for Bosnia and Herzegovina, .hr for Croatia, .me for Montenegro, .mk for North Macedonia, .rs for Serbia and .si for Slovenia), .zr for Zaire (now .cd for the Democratic Republic of the Congo), and .an for Netherlands Antilles (now .aw for Aruba, .cw for Curaçao and .sx for Sint Maarten). In contrast to these, the TLD .su has remained active despite the collapse of the Soviet Union that it represents. Under the chairmanship of Nigel Roberts, ICANN's ccNSO is working on a policy for the retirement of ccTLDs that have been removed from ISO 3166.

{{Further|Proposed top-level domain}}

Around late 2000, ICANN discussed and finally introduced{{cite web |title=InterNIC FAQs on New Top-Level Domains |publisher=Internic.net |date=2002-09-25 |url=https://www.internic.net/faqs/new-tlds.html |access-date=2013-03-28}} .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, to address the responsibility of US service providers under the US Communications Decency Act of 1996. Several options were proposed including xxx, sex and adult.[https://datatracker.ietf.org/doc/html/rfc3675 RFC 3675:] .sex Considered Dangerous The .xxx top-level domain eventually went live in 2011.{{cite web |title=What is top-level Domain {{!}} TLD meaning - Namecheap |url=https://www.namecheap.com/domains/what-is-a-tld-definition/ |access-date=2023-06-26 |website=namecheap.com}}

An older proposal consisted of seven new gTLDs: arts, firm, .info, nom, rec, .shop, and .web.{{cite web |title=(historical) gTLD MoU |url=http://www.gtld-mou.org/docs/faq.html#2.1 |url-status=dead |archive-url=https://web.archive.org/web/20080613083133/http://www.gtld-mou.org/docs/faq.html#2.1 |archive-date=13 June 2008}} 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".{{cite web |title=32nd International Public ICANN Meeting |publisher=ICANN |date=22 June 2008 |url=https://archive.icann.org/en/meetings/paris2008/}} This program envisioned the availability of many new or already proposed domains, as well as a new application and implementation process.{{cite web |date=15 June 2009 |title=New gTLD Program |url=https://www.icann.org/en/topics/new-gtld-program.htm |url-status=dead |archive-url=https://web.archive.org/web/20090617071629/https://www.icann.org/en/topics/new-gtld-program.htm |archive-date=17 June 2009 |access-date=15 June 2009 |publisher=ICANN}} Observers believed that the new rules could result in hundreds of new gTLDs being registered.[https://circleid.com/posts/86269_icann_approves_overhaul_top_level_domains/ ICANN Board Approves Sweeping Overhaul of Top-level Domains], CircleID, 26 June 2008.

On 13 June 2012, ICANN announced nearly 2,000 applications for top-level domains, which began installation throughout 2013.{{cite web |title=The Top 10 Proposed New Top Level Domains So Far |url=https://www.pcworld.com/article/465250/the_top_10_proposed_new_top_level_domains_so_far.html |access-date=12 June 2012}}{{cite web |title=Reveal Day 13 June 2012 – New gTLD Applied-For Strings |publisher=Newgtlds.icann.org |url=https://newgtlds.icann.org/en/program-status/application-results/strings-1200utc-13jun12-en |access-date=2013-03-28 |url-status=dead |archive-url=https://web.archive.org/web/20120615092059/https://newgtlds.icann.org/en/program-status/application-results/strings-1200utc-13jun12-en |archive-date=15 June 2012}} The first seven – bike, clothing, guru, holdings, plumbing, singles, and ventures – were released in 2014.{{cite web |title=What the new top-level domains from ICANN mean for you - Digital Trends |website=Digital Trends |date=5 February 2014 |url=https://www.digitaltrends.com/computing/will-new-top-level-domains-change-use-web/}}

ICANN rejected several proposed domains to include .home and .corp due to conflicts regarding gTLDs that are in use in internal networks.

Investigation into the conflicts was conducted at ICANN's request by Interisle Consulting. The resulting report was to become known as the Name Collision{{cite web |title=Name Collision |website=ICANN Wiki |url=https://icannwiki.org/Name_Collision |access-date=5 July 2021}} issue, which was first reported at ICANN 47.{{cite web |title=ICANN 47 |website=ICANN Wiki |url=https://icannwiki.org/ICANN_47 |access-date=5 July 2021}}

File:DNS schema.svg[.] is a node in the DNS tree, just like wikipedia.[org.] and en.[wikipedia.org.]. As such, it has its own DNS records.]]

Due to the structure of DNS, each node in the tree has its own collection of records, and since top-level domains are nodes in DNS, they have records of their own. For example, querying org itself (with a tool such as dig, host, or nslookup) returns information on its nameservers:

QUESTION

org. IN ANY

ANSWER

org. 21599 IN NS a0.org.afilias-nst.info.

org. 21599 IN NS a2.org.afilias-nst.info.

org. 21599 IN NS b0.org.afilias-nst.org.

org. 21599 IN NS b2.org.afilias-nst.org.

[…]

Dotless domains are top-level domains that take advantage of that fact, and implement A, AAAA or MX DNS records to serve webpages or allow incoming email directly on a TLD – for example, a webpage hosted on http://example/, or an email address user@example.{{cite web |title=SSAC Report on Dotless Domains |publisher=ICANN |date=24 August 2012 |url=https://www.icann.org/en/public-comment/proceeding/ssac-report-on-dotless-domains-24-08-2012 |access-date=14 August 2021}}

ICANN and IAB have spoken out against the practice, classifying it as a security risk among other concerns.{{cite web |title=IAB Statement: Dotless Domains Considered Harmful |publisher=Internet Architecture Board |year=2013 |url=https://www.iab.org/documents/correspondence-reports-documents/2013-2/iab-statement-dotless-domains-considered-harmful/ |access-date=14 August 2021}} ICANN's Security and Stability Advisory Committee (SSAC) additionally claims that SMTP "requires at least two labels in the FQDN of a mail address" and, as such, mail servers would reject emails to addresses with dotless domains.

ICANN has also published a resolution in 2013 that prohibits the creation of dotless domains on gTLDs.{{cite web |title=Approved Resolutions {{!}} Meeting of the New gTLD Program Committee |url=https://www.icann.org/en/board-activities-and-meetings/materials/approved-resolutions-meeting-of-the-new-gtld-program-committee-13-08-2013-en}} ccTLDs, however, fall largely under their respective country's jurisdiction, and not under ICANN's. Because of this, there have been many examples of dotless domains on ccTLDs in spite of ICANN's vocal opposition.

As of September 2023, that is the case of:

• Anguilla's .ai, online at http://ai./ ({{webarchive|url=https://archive.today/20230122060348/http://ai/|date=22 January 2023}})
  It simply displays a notice that the website is no longer public.
• Uzbekistan's .uz, online at https://uz./ ({{webarchive|url=https://archive.today/20230904155401/https://uz/|date=4 September 2023}})
  It's a mirror of https://cctld.uz/, albeit with an invalid certificate.

Other ccTLDs with A or AAAA records, as of September 2023, include: .cm, .tk and .ws.

A similar query to org{{'}}s presented above can be made for ai, which shows A and MX records for the TLD:

QUESTION

ai. IN ANY

ANSWER

ai. 21599 IN A 209.59.119.34

ai. 21599 IN MX 10 mail.offshore.ai.

ai. 21599 IN NS anycastdns1-cz.nic.ai.

ai. 21599 IN NS anycastdns2-cz.nic.ai.

ai. 21599 IN NS pch.whois.ai.

[…]

Historically, many other ccTLDs have had A or AAAA records. On 3 September 2013, as reported by the IETF, they were the following:{{cite news |title=Top-Level Domains That Are Already Dotless |first1=John |last1=Levine |first2=Paul |last2=Hoffman |newspaper=Ietf Datatracker |publisher=Internet Engineering Task Force |date=December 2013 |url=https://datatracker.ietf.org/doc/html/rfc7085 |access-date=14 August 2021}} .ac, .dk, .gg, .io, .je, .kh, .sh, .tm, .to, and .vi.

Following a 2014 resolution by ICANN, newly registered TLDs must implement the following A, MX, TXT, and SRV apex DNS records – where stands for the registered TLD – for at least 90 days:{{cite web |title=Name Collision Occurrence Assessment |first=Akram |last=Atallah |publisher=ICANN |date=4 August 2014 |url=https://newgtlds.icann.org/sites/default/files/agreements/name-collision-assessment-04aug14-en.htm |access-date=17 August 2021}}

. 3600 IN MX 10 your-dns-needs-immediate-attention..

. 3600 IN SRV 10 10 0 your-dns-needs-immediate-attention..

. 3600 IN TXT "Your DNS configuration needs immediate attention see https://icann.org/namecollision"

. 3600 IN A 127.0.53.53

This requirement is meant to avoid domain name collisions when new TLDs are registered. For example, programmers may have used custom local domains such as foo.bar or test.dev, which would both collide with the creation of gTLDs .bar in 2014 and .dev in 2019.

While this does create apex DNS records of type A and MX, they do not qualify as a dotless domain, as the records should not point to real servers. For instance, the A record contains the IP 127.0.53.53, a loopback address (see IPv4 § Addressing), picked as a mnemonic to indicate a DNS-related problem, as DNS uses port 53.{{cite web |title=Name Collision Resources & Information |publisher=ICANN |url=https://www.icann.org/resources/pages/name-collision-2013-12-06-en |access-date=17 August 2021}}

{{Main|Pseudo-top-level domain}}

{{More citations needed|section|date=December 2018}}

Several networks, such as BITNET, CSNET, and UUCP, existed that were in widespread use among computer professionals and academic users, but were not interoperable directly with the Internet and exchanged mail with the Internet via special email gateways. For relaying purposes on the gateways, messages associated with these networks were labeled with suffixes such as .bitnet, .oz, .csnet, or .uucp, but these domains did not exist as top-level domains in the public Domain Name System of the Internet.

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, and pseudo-domains now largely survive as historical relics. One notable exception is the 2007 emergence of SWIFTNet Mail, which uses the swift pseudo-domain.{{cite web |title=SWIFTNet Mail now available |publisher=SWIFT |date=16 May 2007 |url=https://www.swift.com/about_swift/press_room/swift_news_archive/home_page_stories_archive_2007/mail_now_available.page |access-date=3 January 2010 |archive-date=29 June 2009 |archive-url=https://web.archive.org/web/20090629013837/http://www.swift.com/about_swift/press_room/swift_news_archive/home_page_stories_archive_2007/mail_now_available.page |url-status=dead }}

The anonymity network Tor formerly used the top-level pseudo-domain .onion for onion services, which can only be reached with a Tor client because it uses the Tor onion routing protocol to reach the hidden service to protect the anonymity of users. However, the pseudo-domain became officially reserved in October 2015.{{Cite report |url=https://www.rfc-editor.org/rfc/rfc7686 |title=The ".onion" Special-Use Domain Name |last1=Appelbaum |first1=Jacob |last2=Muffett |first2=Alec |date=October 2015 |publisher=Internet Engineering Task Force |issue=RFC 7686}} i2p provides a similar hidden pseudo-domain, .i2p,{{Cite web |title=Naming and Address Book - I2P |url=https://geti2p.net/en/docs/naming |access-date=2024-10-25 |website=geti2p.net}} and Namecoin uses the .bit pseudo-domain.{{Cite web |title=Dot-Bit |url=https://www.namecoin.org/dot-bit/ |access-date=2024-10-25 |website=www.namecoin.org}}

==Examples==

• Alternative DNS root
• Domain hack
• Domain name registrar
• List of Internet top-level domains
• Public Suffix List
• Second-level domain

{{notelist}}

{{Reflist}}

• [https://web.archive.org/web/20040124074709/http://www.addressingtheworld.info/ Addressing the World]: National Identity and Internet Country Code Domains, edited by Erica Schlesinger Wass (Rowman & Littlefield, 2003, {{ISBN|0-7425-2810-3}}) examines connections between cultures and their ccTLDs.
• [https://mitpress.mit.edu/9780262632980/ruling-the-root/ Ruling the Root] by Milton Mueller (MIT Press, 2001, {{ISBN|0-262-13412-8}}) discusses TLDs and domain name policy more generally.

{{Commons category|Top-level domains}}

{{Wikidata property|P78}}

• [https://www.iana.org/domains/root/db Root Zone Database] – list of TLDs on the DNS Root Zone, IANA
• [https://data.iana.org/TLD/tlds-alpha-by-domain.txt IANA TLD List] (plain text, ALL-CAPS)
• [https://circleid.com/topics/new_tlds New TLDs] – Articles on CircleID about TLDs
• {{cite web |title=Top-Level Domain Names by Host Count |publisher=ISC |date=January 2008 |url=https://ftp.isc.org/www/survey/reports/current/bynum.txt |access-date=7 August 2008}}
• [https://web.archive.org/web/20120615092059/http://newgtlds.icann.org/en/program-status/application-results/strings-1200utc-13jun12-en TLDs accepted in 2012] (archived)

{{-}}

{{Generic top-level domains}}

Category:Domain Name System

Category:Identifiers

Category:Internet governance

Category:1980s establishments

Category:Computer-related introductions in the 1980s