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Domain name

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A domain name is a text-based string used to identify resources on the Internet. These resources include computers, networks, and various digital services like websites or email.

An annotated example of a domain name
An annotated example of a domain name

While computers communicate using numerical Internet Protocol (IP) addresses, these numbers are difficult for humans to memorize. Domain names provide an abstraction, replacing complex numbers with recognizable words. This system allows a resource to change its physical location or IP address without changing its name. This flexibility is essential for the modern, moving parts of the global network.

Domain names function through a hierarchical structure known as the Domain Name System (DNS). This system is organized like an inverted tree. At the very top is the DNS root domain, which is technically nameless. From this root, the hierarchy descends through various levels of subordinate labels. Each label is a part of the name separated by a dot. For example, in the name "www.example.com," the labels are "www," "example," and "com."

DNS schema
DNS schema

This structure allows for organized, scalable naming across the entire Internet.

The highest level of this hierarchy consists of top-level domains (TLDs). There are two primary types of TLDs. The first are generic top-level domains (gTLDs), which represent specific categories. Common examples include "com" for commercial use, "org" for organizations, and "edu" for education. The second type are country code top-level domains (ccTLDs). These use two-letter codes to represent specific territories.

Domain name space
Domain name space

Below these TLDs are second-level and third-level domains. These lower levels are often reserved by end-users through a domain name registrar. A domain name that includes every single label in the hierarchy is called a fully qualified domain name (FQDN).

Understanding the syntax of these names is important for technical accuracy. Each individual part of a domain name is called a label. A label can contain between 1 and 63 octets. The entire domain name cannot exceed a total length of 253 ASCII characters. While labels are case-insensitive, they are most commonly written in lowercase in technical contexts.

DNS schema
DNS schema

When a domain name is associated with at least one IP address, it is also referred to as a hostname. This term is often used to identify specific host computers on a network.

The history of domain names traces back to the ARPANET era. Before the modern Internet, researchers used a central file called "host.txt" to map names to numbers. This file was retrieved from a computer at SRI. However, as the network grew rapidly, a single central registry became impossible to maintain. To solve this, the Domain Name System was introduced in 1983. It was published by the Internet Engineering Task Force as RFC 882 and RFC 883. This change allowed the Internet to scale to its current massive size.

Today, the management of the domain name space is a highly organized global effort. The Internet Corporation for Assigned Names and Numbers (ICANN) manages the top-level architecture. ICANN authorizes registrars, which are the entities that sell domain names to the public. It is important to note that registering a name does not grant legal ownership. Instead, it grants an exclusive right to use that name for a specific duration.

An annotated example of a domain name
An annotated example of a domain name

In some cases, the use of domain names in commerce may be subject to trademark law.

Domain names have evolved significantly since the 1980s. Originally, there were only seven generic TLDs: "com," "net," "org," "edu," "gov," "mil," and "int." As the Internet expanded, the need for more names grew. In 2008, ICANN began a process to introduce many more generic TLDs. By 2016, the number of live gTLDs had reached 1,000. This expansion allows for much more specific naming, such as using brand names or industry terms. This continuous growth ensures that the naming system can keep up with new technologies and users.

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File:An annotated example of a domain name.png
An annotated example of a domain name.png
File:Domain name space.svg
Domain name space.svg
File:DNS schema.svg
DNS schema.svg
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