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. Each TLD is managed by a single registry.

Varieties of TLDs

There are different types of TLDs.

• gTLDs, which includes sTLDs and brand TLDs.
• ccTLDs
• geoTLDs

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).

History

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.

Innovations

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.

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. 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.

Chinese version of this page/本页中文版

顶级域

顶级域（顶级域，有时也称为字符串）指的是位于一个域名最后的部分，比如，.com、 .net、.us、.info等等。 每一个顶级域都由一个单独的注册局管理。

顶级域的种类

顶级域可以分为不同的类型。

• 通用顶级域，其中包括赞助类顶级域 和品牌类顶级域。
• 国家代码顶级域
• 地理类顶级域

上述顶级域的运作方式各不相同，但是可以通过一些简单的途径进行归类：

• 运作模式：
  • 开放型 – 运作并且提供注册和解析服务
  • 封闭型 – 不接受注册，可以解析遗产/基础设施类子域名。
• 限制的级别：
  • 无限制类– 如果不需要满足任何条件就可以注册一个顶级域下的域名时，这样的顶级域称为无限制顶级域。
  • 限制类 – 要求具有本地物理地址，本地税号或符合其他特定条件才能注册域名的顶级域。
  • 赞助类 – 是限制类顶级域的一个变体，申请赞助类顶级域中域名的申请人必须符合该顶级域的要求（比如，.jobs会要求人力资源的参与，.travel会要求必须符合特定的旅行条件等等）

历史

在20世纪80年代初期，随着互联网在学术界的普及，人们对分层式域名系统的需求开始凸显，并最终形成了一个分散式的互联网。斯坦福研究所网络信息中心与其他机构的沟通中包含了创建一个分层式域名系统的计划，内容可以参考1982年形成的一份团体文件RFC 805。文件中概括了许多形成最终域名系统的基本要素，包括要求创建顶级域从而形成查询的固定起始点，以及形成独特赞助类顶级域的要求。由此也促使形成一个注册商类型的行政机构，也让初期的IT社区意识到将每个域名的责任分配到单个的域名服务器所具有的管理优势。

改革

在2009年的首尔会议中，互联网名称与数字地址分配机构（ICANN）批准了国家代码顶级域 国际化域名的快速跟踪流程，从而允许国家代码顶级域中可以使用非拉丁字符。俄罗斯、埃及、沙特阿拉伯和阿联酋是首批进行申请和执行的国家。

经过6年的开发以后，ICANN在2011年6月的新加坡会议中推出了新通用顶级域项目。这个无限制的扩展项目在互联网历史中首次允许所有人申请运作几乎所有的字符串。. 2012年6月13日（揭晓日），其宣布共有1,930申请：其中有84份为社区申请，116份为针对国际化域名的申请，还有230份申请拥有一名或多名申请人，因此需要通过字符串争用进行解决。这意味着“新通用顶级域项目”的首轮扩展将最多产生1,409个新通用顶级域。

Chinese translation of this page provided thanks to TLD Registry Ltd.