Top-Level Domain

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The Top Level Domain (TLD, also sometimes referred to as a string) is the last part of a domain name, for example, .com, .net, .us, .info, etc.[1] Each TLD is managed by a single registry.

Varieties of TLDs

There are different types of TLDs.

These TLDs operate in different manners, and can be categorized in some simple ways:

  • Operating Mode:
    • Open - Operating and offering both registration and resolution services.
    • Closed - Not accepting registrations, may be resolving evergreen/legacy/infrastructure subdomains.
  • Level of Restriction:
    • Unrestricted - If there are no requirements that must be met in order to register a name under a TLD, that TLD is Unrestricted.
    • Restricted - Requiring Local Physical Address, Local Tax ID, or other specific criteria be met to qualify in order to provision a name.
    • Sponsored - A variation on Restricted, the applicant for a domain in an STLD must meet the requirements within that TLD (ie. .jobs would require that Human Resources be involved, .travel would require certain Travel criteria are met, etc).


The need for a hierarchical DNS arose with the popularity of the Internet in academic spheres in the early 1980s, which eventually necessitated a decentralized Internet. Communications between The Stanford Research Institute NIC and other institutions included plans to create a hierarchical DNS, and can be found in RFC 805, a group document from 1982. This document outlines many of the basics of the eventual DNS, including the need for TLDs to provide a fixed starting point for queries, and the need for SLDs to be unique. This, in turn, would necessitate the need for a registrar type of administration, and help the nascent IT community recognize that the distribution of responsibility for each domain to individual name servers would provide administrative advantages.[2]


At its Seoul conference in 2009, ICANN approved the IDN ccTLD Fast Track process, which allowed ccTLDs to be written in non-latin characters. Russia, Egypt, Saudi Arabia, and United Arab Emirates are some of the first countries to advance in the application and implementation process.[3]

Following a six year development process, ICANN launched the New gTLD Program at its Singapore conference in June, 2011. This unlimited expansion program allowed anyone to apply to run nearly any string for the first time in the history of the Internet.[4] On June, 13th, 2012 ("Reveal Day"), it was announced that there were 1,930 applications: 84 of these were community applications, 116 are for IDNs, and 230 of the applications have one or more applicant and will thus go through string contention processes. This means the first round of the new gTLD program could create a maximum of 1,409 new TLDs.[5]