FQDN (fully qualified domain name)

A fully qualified domain name (FQDN) is a complete domain name that uniquely identifies a specific computer, host, or network on the internet. It is composed of multiple parts that are separated by dots, with each part indicating a specific level of the domain hierarchy. The FQDN is used to locate and access resources on the internet, such as websites, email servers, and other network services.

The structure of an FQDN can be broken down into three main parts: the hostname, the domain name, and the top-level domain (TLD). Let's take a closer look at each of these components and how they work together to create a fully qualified domain name.

Hostname: The hostname is the unique name assigned to a specific computer or device on a network. It typically consists of a name or label followed by a domain name. For example, in the FQDN "www.example.com", "www" is the hostname.

Domain Name: The domain name is a sequence of one or more labels that identify a specific domain or subdomain within the DNS (Domain Name System) hierarchy. Each label is separated by a dot, and the entire sequence of labels is read from right to left. For example, in the FQDN "www.example.com", "example" is the domain name.

Top-Level Domain (TLD): The top-level domain (TLD) is the last part of the domain name and is used to indicate the type of organization or geographical location of the domain. Some common TLDs include ".com" for commercial organizations, ".org" for non-profit organizations, and ".edu" for educational institutions.

To create a fully qualified domain name, the hostname is combined with the domain name and top-level domain to form a complete, hierarchical address. For example, the FQDN "www.example.com" is composed of the hostname "www", the domain name "example", and the top-level domain "com".

FQDNs are used in a variety of contexts, including DNS lookups, email delivery, and web browsing. When you type a URL into your web browser, it uses the FQDN to locate the web server hosting the requested content. Similarly, when you send an email, the FQDN is used to locate the mail server responsible for delivering the message.

In addition to the basic components of an FQDN, there are a number of other elements that can be included to provide additional information about the domain or its associated resources. These include:

Subdomains: Subdomains are additional levels of the domain hierarchy that can be used to create more specific addresses within a larger domain. For example, "blog.example.com" is a subdomain of "example.com".

Aliases: Aliases are alternative domain names that are used to refer to the same resource. For example, "www.example.com" and "example.com" may both be used to refer to the same website.

IP Addresses: IP addresses are numerical addresses used to identify specific computers or devices on a network. They can be used instead of an FQDN to access network resources directly.

MX Records: MX records are used to specify the mail servers responsible for handling email delivery for a specific domain.

TXT Records: TXT records are used to store arbitrary text data associated with a domain. They are commonly used for domain verification and authentication purposes.

In conclusion, a fully qualified domain name (FQDN) is a complete and hierarchical address that uniquely identifies a specific computer, host, or network on the internet. It is composed of a hostname, a domain name, and a top-level domain (TLD), and can be further extended with subdomains, aliases, and additional resource records. FQDNs are used in a variety of contexts, including DNS lookups, email delivery,