TLD Concept

A top-level domain (TLD), sometimes referred to as a top-level domain name (TLDN), is the last part of an Internet domain name; that is, the letters which follow the final dot of any domain name. For example, in the domain name www.sexhugs.com, the top-level domain is com (or COM, as domain names are not case-sensitive). Management of most top-level domains is delegated to responsible parties or organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.


Generic TLDs

In the 1980s, seven gTLDs (.com, .edu, .gov, .int, .mil, .net, and .org) were created. Domain names may be registered in three of these (.com, .net, and .org) without restriction; the other four have limited purposes.

Over the next twelve years, various discussions occurred concerning additional gTLDs, leading to the selection in November 2000 of seven new TLDs for introduction. These were introduced in 2001 and 2002. Four of the new TLDs (.biz, .info, .name, and .pro) are unsponsored. The other three new TLDs (.aero, .coop, and .museum) are sponsored.

Generally speaking, an unsponsored TLD operates under policies established by the global Internet community directly through the ICANN process, while a sponsored TLD is a specialized TLD that has a sponsor representing the narrower community that is most affected by the TLD. The sponsor thus carries out delegated policy-formulation responsibilities over many matters concerning the TLD.

Domain Name Examples

Examples:

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:

URL: http://www.yourfinancer.com/
Domain name: www.yourfinancer.com
Registered domain name: yourfinancer.com

As a general rule, the IP address and the server name are interchangeable. For most Internet services, the server will not have any way to know which was used. However, the explosion of interest in the Web means that there are far more Web sites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature goes under the name virtual hosting and is commonly used by Web hosts.

For example, as referenced in RFC 2606 (Reserved Top Level DNS Names), the server at IP address 208.77.188.166 handles all of the following sites:

sexhugs.com
www.sexhugs.com
knowbabe.com
www.knowbabe.com
yourfinancer.com
www.yourfinancer.com

When a request is made, the data corresponding to the hostname requested is provided to the user.

Basic idea of Domain

The term domain name has multiple related meanings:

* A name that identifies a computer or computers on the Internet. These names appear as a component of a Web site's URL, e.g. www.knowbabe.com . This type of domain name is also called a hostname.
* The product that domain name registrars provide to their customers. These names are often called registered domain names.
* Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domain names like .com, or the names used by the Session Initiation Protocol (VoIP), or DomainKeys.
* They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".

This article will primarily discuss registered domain names. See the Domain Name System article for technical discussions about general domain names and the hostname article for further information about the most common type of domain name.

Basic Concepts:

The most common types of domain names are hostnames that provide more recognizable names to stand in for numeric IP addresses. They allow for any website to move to a different location in the topology of the Internet (or an intranet), which would then have a different IP address.

By allowing the use of unique alphabetical addresses instead of numeric ones, domain names allow Internet users to more easily find and communicate with web sites and other server-based services. The flexibility of the domain name system allows multiple IP addresses to be assigned to a single domain name, or multiple domain names to be assigned to a single IP address. This means that one server may have multiple roles (such as hosting multiple independent websites), or that one role can be spread among many servers. One IP address can also be assigned to several servers, as used in anycast and hijacked IP space.

Hostnames are restricted to the ASCII letters a through z (case-insensitive), the digits 0 through 9, and the hyphen, with some other restrictions. Registrars restrict the domains to valid hostnames, because they otherwise would be useless. The Internationalized domain name (IDN) system has been developed to bypass the restrictions on character allowances in hostnames, making it easier for users of non-English alphabets to be used on the Internet. The underscore character is frequently used to ensure that a domain name is not recognized as a hostname, as with the use of SRV records, for example, although some older systems such as NetBIOS did allow it. To avoid confusion and for other reasons, domain names with underscores in them are sometimes used where hostnames are required.

Domain names are often referred to simply as domains and domain name registrants are frequently referred to as domain owners, although domain names, technically, are leased from a registrar.