Which of the following is an example of a top level domain

Top-level domains are also known as domain suffixes.

Historically, TLDs represented the purpose and type of domain or the geographical area from which it originated. ICANN has generally been very strict about opening up new TLDs, but in 2010, it decided to allow the creation of numerous new generic TLDs as well as TLDs for company-specific trademarks.

The Internet Corporation for Assigned Names and Numbers (ICANN), is the entity that coordinates domains and IP addresses for the internet.

Examples of some of the popular TLDs include:

TLDs are mainly classified into two categories: generic TLDs and country-specific TLDs.

For example, in the internet address: https://www.google.com, the “.com” portion is the TLD.

Top-level domain (TLD) refers to the last segment of a domain name, or the part that follows immediately after the “dot” symbol.

Techopedia Explains Top-Level Domain (TLD)

ARPANET created TLDs to allow humans to ease the process of memorizing IP addresses. Instead of using a series of digits for each computer, the domain name system was established to organize addresses in a more user-friendly way.

In 1971, the first email was developed and sent using an “@” symbol. The “address” after the @ was not the domain but the actual computer it was sending to. In the early 1980s, when the earliest domains started being developed, the first TLDs such as .org and .com saw the light.

A top-level domain recognizes a certain element regarding the associated website, such as its objective (business, government, education), its owner, or the geographical area from which it originated.

Each TLD includes an independent registry controlled by a specific organization, which is managed under the guidance of the Internet Corporation for Assigned Names and Numbers (ICANN).

ICANN recognizes the following types of TLDs:

Generic Top-Level Domains (gTLD)

These are the most popular types of TDLs. Some examples include “.edu” for educational sites and .”com” for commercial sites. These types of TLDs are available for registration.

Country-Code Top-Level Domains (ccTLD)

Every ccTLD recognizes a specific country and is generally two letters long. For example, the ccTLD for Australia is “.au”.

These TLDs are supervised by private organizations.

Infrastructure Top-Level Domains

There is only one TLD in this category, which is “.arpa”. The Internet Assigned Numbers Authority controls this TLD for the Internet Engineering Task Force (IETF).

In earlier times, the purpose of each TLD was specific, such as .com which was used only for commercial websites. Eventually, as the Internet kept growing and evolving, this restriction was abandoned, and now there’s almost no distinction between most TLDs.

However, some TLDs are reserved for some unique purposes even today, such as gTLDs that are assigned for educational institutions (.edu) and those assigned for government and the military (.gov and .mil).

Some of the TLDs and their original explanations are as follows:

  • .com — Commercial businesses.

  • .org — Organizations (generally charitable).

  • .net — Network organizations.

  • .gov — U.S. government agencies.

  • .mil — Military.

  • .edu — Educational facilities, like universities.

  • .th — Thailand.

  • .ca — Canada.

  • .au — Australia.

According to the IETF, there are four top-level domain names that are reserved, and are not used in production networks inside the worldwide domain name system:

  • .example — Only available to use in examples.

  • .invalid — Only available to use in invalid domain names.

  • .localhost — Only available to use in local computers.

  • .test — Only available to use in tests.

Currently, some TLDs are more difficult to get compared to easy ones such as .com. Because of this, many organizations register multiple TLDs and redirect them as necessary to the main one used for their principal web resource.

Domain at the highest level of the DNS hierarchy

A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain.[10] 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 non empty label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com. Responsibility for management of most top-level domains is delegated to specific organizations by the ICANN, an Internet multi-stakeholder community, 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: Countries, Categories, and Multiorganizations.[11] An additional temporary group consisted of only the initial DNS domain, arpa,[12] and was intended for transitional purposes toward the stabilization of the domain name system.





As of 2015, IANA distinguishes the following groups of top-level domains:[13]

Countries are designated in the Domain Name System by their two-letter ISO country code;[14] 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/.

Internationalized country code TLDs




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,[15] 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.[16]

Infrastructure domain




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.

Reserved domains




A set of domain names is reserved[17][18] by the Internet Engineering Task Force as special-use domain names per authority of Request for Comments (RFC) 6761. The practice originated in RFC 1597 for reserved address allocations in 1994, and reserved top-level domains in RFC 2606 of 1999. RFC 6761 reserves the following four top-level domain names to avoid confusion and conflict.[19] 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 invalid domain names
  • localhost: reserved to avoid conflict with the traditional use of localhost as a hostname
  • test: reserved for use in tests

RFC 6762 reserves the use of .local for link-local host names that can be resolved via the Multicast DNS name resolution protocol.[20]

RFC 7686 reserves the use of .onion for the self-authenticating names of Tor onion services. These names can only be resolved by a Tor client because of the use of onion routing to protect the anonymity of users.[21]

Internet-Draft draft-wkumari-dnsop-internal-00 proposes reserving the use of .internal for “names which do not have meaning in the global context but do have meaning in a context internal to their network”, and for which the RFC 6761 reserved names are semantically inappropriate.

Historical domains




In the late 1980s, InterNIC created the nato domain for use by NATO.[citation needed] 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]

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), and zr for Zaire (now cd for the 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. Under the chairmanship of Nigel Roberts, ICANN’s ccNSO is working on a policy for retirement of ccTLDs that have been removed from ISO 3166.

Proposed domains




Around late 2000, ICANN discussed and finally introduced[22] 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.[23] The xxx top-level domain eventually went live in 2011.[citation needed]

An older proposal consisted of seven new gTLDs: arts, firm, info, nom, rec, shop, and web.[24] 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”.[25] This program envisioned the availability of many new or already proposed domains, as well as a new application and implementation process.[26] Observers believed that the new rules could result in hundreds of new gTLDs being registered.[27]

On 13 June 2012, ICANN announced nearly 2,000 applications for top-level domains, which began installation throughout 2013.[28][29] The first seven – bike, clothing, guru, holdings, plumbing, singles, and ventures – were released in 2014.[30]

Rejected domains




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[31] issue, which was first reported at ICANN 47.[32]

Dotless domains




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

is a node in the DNS tree, just likeand. 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:

QUESTIONorg. IN ANYANSWERorg. 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 [email protected].[33]

ICANN and IAB have spoken out against the practice, classifying it as a security risk among other concerns.[34] 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.[33]

ICANN has also published a resolution in 2013 that prohibits the creation of dotless domains on gTLDs.[35] 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 August 2021, that is the case of Anguilla’s .ai, online at http://ai./ (as a mirror of http://offshore.ai/), and of Uzbekistan’s .uz, online at https://uz./ (as a mirror of https://cctld.uz/, albeit with an invalid certificate). Other ccTLDs with A or AAAA records, as of August 2021, include: .bh, .cm, .pn, .tk, .va, and .ws.

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

QUESTIONai. IN ANYANSWERai. 21599 IN A 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:[36] .ac, .dk, .gg, .io, .je, .kh, .sh, .tm, .to, and .vi.

New TLDs




Following a 2014 resolution by ICANN, newly registered TLDs must implement the following A, MX, TXT, and SRV apex DNS records – where <TLD> stands for the registered TLD – for at least 90 days:[37]

<TLD>. 3600 IN MX 10 your-dns-needs-immediate-attention.<TLD>.<TLD>. 3600 IN SRV 10 10 0 your-dns-needs-immediate-attention.<TLD>.<TLD>. 3600 IN TXT "Your DNS configuration needs immediate attention see https://icann.org/namecollision"<TLD>. 3600 IN A

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. As of August 2021, top-level domains with these special apex records are .arab, .cpa, .politie, and .watches.

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, a loopback address (see IPv4 § Addressing), picked as a mnemonic to indicate a DNS-related problem, as DNS uses port 53.[38]

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.[39]

The anonymity network Tor formerly used the top-level pseudo-domain onion for Tor hidden 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. i2p provides a similar hidden pseudo-domain, .i2p.

BT hubs use the top-level pseudo-domain .home for local DNS resolution of routers, modems and gateways.

See also








Further reading




  • 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.
  • Ruling the Root by Milton Mueller (MIT Press, 2001, ISBN 0-262-13412-8) discusses TLDs and domain name policy more generally.
Written by Jane