What is a top-level domain?

Top-level Domains come at the end of domain names, and are important for classifying domain names, as well as essential for DNS lookups.

Leerdoelen

Na het lezen van dit artikel kun je:

  • Define what top-level domains are
  • Understand the purpose of TLDs
  • Outline the different types of TLDs

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What is a top-level domain (TLD)?

In the DNS hierarchy, a top-level domain (TLD) represents the first stop after the root zone. In simpler terms, a TLD is everything that follows the final dot of a domain name. For example, in the domain name ‘google.com’, ‘.com’ is the TLD. Some other popular TLDs include ‘.org’, ‘.uk’, and ‘.edu’.

TLDs play an important role in the DNS lookup process. For all uncached requests, when a user enters a domain name like ‘google.com’ into their browser window, the DNS resolvers start the search by communicating with the TLD server. In this case, the TLD is ‘.com’, so the resolver will contact the TLD DNS server, which will then provide the resolver with the IP address of Google’s origin server.

The Internet Corporation for Assigned Names and Numbers (ICANN) has authority over all TLDs used on the Internet, and it delegates the responsibility of these TLDs to various organizations. For example, a U.S. company called VeriSign operates all ‘.com’ and ‘.net’ TLDs.

Another purpose of TLDs is to help classify and communicate the purpose of domain names. Every TLD will tell you something about the domain that precedes it; let’s look at some examples:

  • ’.com’ is intended for commercial businesses.
  • ’.gov’ is for U.S. government entities.
  • ’.uk’ is for domains from the United Kingdom.

TLDs themselves are also classified into one of several groups.

What are the different types of TLDs?

  • Generic TLDs: Generic TLDs (gTLDs) encompass some of the more common domain names seen on the web, such as ‘.com’, ‘.net’, and ‘.org’. The Internet Corporation for Assigned Names and Numbers (ICANN) used to heavily restrict the creation of new gTLDs, but in 2010 these restrictions were relaxed. Now there are hundreds of lesser-known gTLDs, such as ‘.top’, ‘.xyz’, and ‘.loan’.
  • Country-code TLDs: Country-code TLDs (ccTLDs) are reserved for use by countries, sovereign states, and territories. Some examples are ‘.uk’, ‘.au’ (Australia), and ‘.jp’ (Japan). The Internet Assigned Numbers Authority (IANA), which is run by ICANN, is in charge of picking appropriate organizations in each location to manage ccTLDs.
  • Sponsored TLDs: These TLDs typically represent professional, ethnic, or geographical communities. Each sponsored TLD (sTLD) has a delegated sponsor that represents that community. For example, ‘.app’ is a TLD intended for the developer community, and it is sponsored by Google. Similarly, ‘.gov’ is intended for use by the U.S. government, and is sponsored by the General Services Administration.
  • Infrastructural TLDs: This category only contains a single TLD: ‘.arpa’. Named for DARPA, the U.S. military research organization that helped pioneer the modern Internet, ‘.arpa’ was the first TLD ever created and is now reserved for infrastructural duties, such as facilitating reverse DNS lookups.
  • Reserved TLDs: Some TLDs are on a reserved list, which means they are permanently unavailable for use. For example, ‘.localhost’ is reserved for local computer environments, and ‘.example’ is reserved for use in example demonstrations.

Do TLDs Matter?

There are now so many TLD options available that the choice can be overwhelming for someone trying to register a new domain name. For years ‘.com’ was seen as the only option for businesses that want to be taken seriously. But experts predict that as the supply of ‘.com’ domains dwindles and some of the newer TLDs continue to pick up steam, we will see a major shift in the perception of alternative TLDs. With big companies like Twitter and Apple starting to adopt alternative TLDs for their products (t.co and itun.es, respectively) we are already seeing that shift in action, so it may be better to create a clever and memorable domain name using an alternative TLD, than to insist on a ‘.com’ domain.