Domain names are an integral part in the domain name system (DNS) infrastructure. Where a URL that includes an IP address would work just fine for your computer to identify a particular location on the web, its coded numbers are much more difficult for people to remember. Consequently, domain names have become the primary means of identifying a web site. Top level domains (TLDs) play an important role in the naming functions associated with the DNS infrastructure. Our guide will examine TLDs in greater detail in order to provide a complete understanding of their function and purpose.
What are TLDs?
Top level domains are the hierarchal pinnacle of the DNS system. A fully-qualified domain name will include it as the final label of the domain in all lower-level domains. TLDs are an integral part of what is considered the root zone of the domain. The URL to a particular page might be:
In this URL, the root zone is:
And the top level domain is:
From this example, you can quickly deduce that there are a wide variety of TLDs available. Some of the common ones include: .org, .net, .gov, .edu, .biz, .info, etc. Let’s take a closer look at where TLDs came from.
What are the 5 most popular Top Level Domain extensions?
The most common domain extension by far is the .com. The .com extension is the daddy of them all. However, .com isn’t the only popular top-level domain out there on the web. There are now hundreds of domain extensions out there available to buy from domain registrars.
The most common types of TLDs are as follows.
.us (United States)
In the top 5 most common domain extensions are ones reserved for a specific use. The .com domain can literally be used by anyone, but some top-level domains are restricted to certain people, governments and educational institutions, such as:
New TLDs Available
Recently, many new TLDs have been created and made available to buy since the original set of extensions were produced. The idea behind them was to create more opportunities for people to create their own unique presence on the internet and to take pressure off of the original set of domain extensions.
Some of these new TLDs were created to serve both a broad use worldwide, and to go niche on special interest groups, such as .ninja, .design, .kitchen and many many more.
Here are a few more examples of new TLDs available to buy.
History of Top Level Domains
When the SNS system was first established, TLD domain space was separated into three groups, including:
At that time there was only a single temporary group, .arpa. The .arpa temporary TLD was created to facilitate transitions in the stabilization of the DNS system.
Internet Corporation for Assigned Names and Numbers (ICANN) was developed to take over the responsibilities to overseeing the establishment of DNS root registries from the National Information Center (InterNIC). One of their functions was the establishment of the Internet Assigned Numbers Authority (IANA). The main function of IANA is to “oversee global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System (DNS), media types, and other Internet Protocol-related symbols and Internet numbers,” according to WikiPedia. The number of TLDs recognized by IANA has grown significantly since its establishment.
Various Groups and Types of TLDs
There are various groups and types of TLDs that have been created by IANA in order to categorize various functions and organizational structures on the internet. Though the list continues to grow, we’ll take a brief look at each of the most common top-level domains that are in use today.
There is a single top-level domain included in this group. That TLD is .arpa, which is the original transitional TLD set up for DNS stabilization. It is maintained by IANA for the same purpose today.
Country Code and Internationalized Country Code TLDs
Of the original groups of TLDs that were established, country code top-level domains are still in existence. They were established as a two-letter code based on their ISO 3166 code, which was set up to identify various countries and the principal subdivisions within them. You probably recognize the following TLDs: .uk, .au, .nz, .mx, or .us. Then there are the ones you wouldn’t think would have a country code like .to domain (Tonga), .ai domain (Anguilla), .gg domain (Guernsey)
Country codes have also been internationalized so that individuals in countries that do not utilize Latin characters can more easily recognize the country codes in the TLDs. Country codes can include, Arabic, Cyrillic, Hebrew or Chinese characters, for example, instead of the common Latin characters more recognizable to English speakers.
Originally labeled as categories in the historical establishment of TLDs, generic top-level domains contain the most recognizable list of TLDs. All generic TLDs must consist of a minimum of three characters or letters. The first generic TLDs consisted of .com, .net, .org, .edu, .gov, .int (international) and .mil, and have obvious connections to their purpose built into their three letter code. Additional generic TLDs have been added, including some you might recognize:
• .app used for apps.
• .info used to provide information.
• .biz used by businesses.
• .global with an obvious international association.
• .host for networking companies.
• .tel used by internet and telecommunications companies.
The list of generic TLDs registered by IANA is exhaustive. It is in a state of continuous growth as organizations look for new ways to compete in the global marketplace and work to create the most recognizable and memorable domain names possible.
Reserved or Restricted TLDs
Reserved or restricted top-level domains create another distinctive group of TLDs. Some examples of reserved or restricted TLDs include:
• .test is reserved for testing purposes.
• .localhost is reserved in order to avoid conflicts when using localhost as a hostname.
• .invalid is utilized to indicate that a domain name is invalid.
• .example is reserved so that it can be used in examples; like the one used above.
• .local is reserved by RFC 6762 for resolving link-local hostnames in DNS protocols.
• .onion is reserved by RFC 7686 as a self-authenticating hostname utilized by Tor. These domain names are utilized to protect user anonymity in the onion-routing system operated by Tor.
These domains serve a specific purpose in the functionality of the internet. Management of these TLDs is handled through official ICANN accredited registrars.
In general, sponsored top-level domains tend to be generic TLDs that are proposed and sponsored by a specific community. Each sponsored TLD is specialized to involved individuals or organizations that are based on ethnic, geographical, professional, technical or other themed concepts. They are most often proposed by organizations or private agencies, which also establish and enforce eligibility and usage rules who register to use their TLD. The most common examples of sponsored TLDs include .gov, .mil, .int, and .edu. Additional sponsored TLDs you might recognize include .tel, .xxx, .museum, .app, and .aero.
The list of top-level domains has continued to grow since the development of the DNS protocol. Many of the TLDs proposed have already been accepted, such as .aero, .biz, .coop, .info, .museum, .name, and .pro, which were proposed in late 2000. Before the acceptance of those proposed TLDs, there was a push to distinguish pornographic or obscene materials using either .xxx, .sex, or .adult, but no top-level domain was established until .xxx went live in 2011. Proposals were also made for .arts, .firm, .nom, and .rec, but IANA felt most of these were covered by existing TLDs. The largest jump in the acceptance of proposed TLDs occurred after an announcement by ICANN in 2012 that they would be adding new generic TLDs to their registered list from more than 2,000 applications. Installation of these new TLDs took place throughout 2013. Today, there a little over 1,000 registered TLDs.
There have also been some TLDs, which existed historically but are no longer in use. One notable top-level domain was the one established by InterNIC for NATO, which was quite obviously .nato. Not long after .nato was established, InterNIC created .int for international organizations in general. NATO was persuaded to use nato.int. After 1996, .nato was removed from the registry.
Most of the historical changes to TLDs have come about in the area of country codes as the names and identities of various nations have evolved. Here are some of the changes that have come about:
• .cs was changed when Czechoslovakia became the Czech Republic .cz and Slovak Republic .sk
• .dd used in East Germany became .de under unified Germany
• .yu was used for SFR Yugoslavia until the country was divided into Bosnia and Herzegovina .ba, Croatia .hr, Montenegro .me, Macedonia .mk, Serbia .rs, Slovenia .si.
• .zr was used for Zaire but was changed to .cd when the country became the Democratic Republic of the Congo.
Also of note is the fact that Russian still maintains the .su country code in spite of the demise of the Soviet Union for which it was created.
There are specialized domain labels that are often used by networks but are not specifically registered as top-level domains. Initially, several networks with widespread among computer professionals and academic users had established codes that were very similar to TLDs. These network names were BITNET, CSNET and UUCP and utilized corresponding suffixes in their domains, but the labels bitnet, oz, csnet, and uucp were never officially TLDs in the public DNS infrastructure. Most of these pseudo-domains have become historical relics though uucp is sometimes seen.
Top-level domains are an integral part of the DNS infrastructure. They are used in the creation of the root address for domain names. Changes made by ICANN and IANA throughout the development of DNS have allowed for more specific and memorable recognition for various types of organizations and specialized groups. As web developers work to create distinctive branding through domain names, the list has grown and continues to grow. With the knowledge you have gained through our guide, you will be better able to recognize what you’re looking at when you see a strange TLD attached to a website or make use of TLDs that more clearly identify your brand niche or organizational objectives.