Top Level Domains Categories

Top Level Domains Categories

February 27, 2025

By Thals Volmar

In this article, we will list the various categories of top level domains, TLDs, according to the classification of the Internet Assigned Numbers Authority (IANA). The latter is the legal entity that manages IP addresses, domain names and other related services. IANA classifies top level domains, TLDs, into categories, at the moment, we have 7 groups of top level domains classified by IANA:

1. Generic top level domain (gTLD).
2. Country code top level domain (ccTLD).
3. Internationalized country code top level domain (IND ccTLD).
4. Sponsored top level domain (sTLD).
5. Restricted generic top level domain (grTLD).
6. Infrastructure top level domain (ARPA).
7. 6) Testing top level domain (tTLD).

We have already discussed three groups of domains on the Domain page, more specifically in the FAQs section; these domain groups are: gTLDs, ccTLDs and sTLDs. These three domain groups are the most common in the sense that their use is not restricted to some extent, except that some sTLDs are subject to rigid registration standards by their sponsor. For a more understanding and quite precise explanations, we will see separately the categories of top level domain:

The category of gTLDs is the most popular, these domains are generally open for registration. We have already defined them as domains that contrast with those of ccTLDs and sTLDs, that being said, anyone can register the gTLDs. Furthermore, to some extent, all gTLDs are regulated by the Internet Corporation for Assigned Names and Numbers, ICANN, while the others are managed by other bodies. In fact, no matter where you are, you can register one or more gTLD(s). To put it simply, the term gTLD is a historical term that does not attach to a specific geographical region or country, but preferably it is universal.

The category of ccTLD is the second most popular worldwide. These domains belong to a specific region or country. We have already defined it, country code top level domain, ccTLD, is a TLD dedicated to and used by a sovereign state identified by the ISO 3166-1 alpha-2 codes. Typically, the TLD of ccTLD consists of 2 letters in reference to the country code it belongs to. The applications of the ccTLD extension started in 1985 with the dot us, the dot uk, and so on. Today many geographical regions have a ccTLD like .eu, .nyc, etc., and almost all countries have their own ccTLD like .de, .fr., .ht, and so on.

The IND ccTLD category is a group of ccTLDs that do not use the ASCII code (American Standard Code for Information Interchange) to display in an Internet browser, preferably these domains are displayed in a non-ASCII character. ICANN, in its Internationalized Domain Name (IDN) Report of June 2024, points out that “IDNs are domain names in different scripts, such as Arabic, Chinese, Latin, and others, using at least one non-ASCII character in the domain name.” In fact, IND ccTLDs differ from ccTLDs altogether in that they do not follow the ASCII standard by using their own characters or scripts.

The category of sTLDs groups domains sponsored by an organization that represents a specific community. We have already defined a sponsored top level domain as being a TLD that has a sponsor representing a specific group or community that is most affected by the scope of the ccTLD and gTLD. The sponsor has delegated authority to develop rules that restrict the general public from registering such a TLD. Typical examples of sTLDs are the .gov (for the US government), .edu (for US higher education institutions), .travel (for the hospitality industry), .aero (for members of the airline industry).

The grTLD category is not a fully recognized category in the domain name system, it seems that the so-called restricted domains are generic domains that are open to the public for registration with pre-established eligibility criteria, however, those who want to register such domain(s) must be able to prove to the entity or entities responsible that they are eligible by submitting documents for example. In these circumstances, grTLDs are normally sponsored generic top level domains; concrete examples are dot mil, dot edu, and so on.

The ARPA (Address and Routing Parameter Area) category called infrastructure top level domain is used mainly in technical network infrastructure management, typically in reverse DNS lookup. The latter uses an IP address to find a domain name which is quite the opposite of the regular DNS lookup which uses a domain name to find an IP address. Unlike the categories of gTLDs, ccTLDs and sTLDs, ARPA domain registration is not allowed.

The last category of TLDs listed in this article is tTLD. A testing top level domain is a domain dedicated to developers of websites, software, etc., in the context of developing their work(s) or carrying out test sequences. That being said, any professional of the kind can use a tTLD without infringing any private domain. The category of tTLDs, besides the free space it offers to developers for testing sessions, is widely used in instructional documentation, development documentation, etc. Typical examples are: .test, .example, .invalid, etc., these TLDs are not open to the general public to register.