Fully Qualified Domain Name (FQDN) explained

Fully Qualified Domain Name (FQDN) is a domain name that specifies the exact location of a host within the tree hierarchy of the Domain Name System (DNS). 

In this scenario, ‘qualified’ means ‘specified’ since the full location of the domain within the DNS tree of hierarchy is specified in the name. 

If the name isn’t fully specified and is missing certain components, it is called a partially qualified domain name, or PQDN.

A FQDN might also be called an absolute domain name since it provides the absolute path of the host.

A FQDN is a domain name that includes a host name, a root domain and a top level domain. It may also include additional subdomains between the root domain and the host name.

Almost all individual parts of a FQDN are technically subdomains. The only part of a domain that isn’t a subdomain is the root domain.

Therefore the TLD and anything after the root domain are subdomains of the absolute domain or FQDN.

For example, the URL ‘www.apple.com‘ is a Fully Qualified Domain Name since it contains a hostname (www) a root domain (.apple) and a top level domain (.com)

FQDN explained.

If a domain name such as ‘apple.com‘ just has a root domain (apple) and a top level domain (.com) the Internet will just assume the host name as (www.)

An incomplete FQDN is referred to as a partially qualified domain name.

A PQDN is a domain name on an internal network that may include a host name and a domain name but does not include an ICANN registered TLD if any at all.

For example, on local network if the name of your computer is (batman), and your company’s domain is (.centre.local), your computer’s partially qualified domain name is batman.centre.local.

At this stage the TLD (.local) is not ICANN registered and can only be used internally; hence the reason it is referred to as a PQDN.

An FQDN can be broken down into three parts:

  • Hostname: mail, ftp, www, etc.
  • Domain: apple, microsoft, ibm, facebook, etc.
  • Top Level Domain (TLD): .com, .net, .org, .br, .co.uk, etc.

A Fully Qualified Domain Name has the format: [hostname].[domain].[tld].

As mentioned before there may also be additional subdomains.

In this instance the format would be as follows: [hostname].[subdomain].[domain].[tld]. And would look something like this: ‘www.shop.apple.com‘ or in most cases would have no (www) as it is assumed and would look like this: ‘shop.apple.com‘.

Please note, there are differences between a subdomain and a root domain even though they may look identical.

Referring back to the apple example, if the domain was to be ‘shop.apple.com‘, and when visited takes you to the shop webpage thats sits on the same server as landing page ‘www.apple.com‘ then (shop) is not a host name but a subdomain.

The root name in this instance is assumed to be (www).

If you were to logon to a internal computer or network remotely through a server seperate to the apple website, for example ‘computer2896.apple.com‘, ‘computer2896’ would be a host name as it is the name of a certain computer or server and has a completely different IP address to that of ‘apple.com‘ and ‘shop.apple.com‘ in which would share the same IP.

The hostname can be used to specify different servers and computers for a single domain.

For example, “mail.example.com” is often the required FQDN format when configuring the SMTP server for an email account.

The FQDN “ftp.example.com” is commonly used when connecting to an FTP server.

Name servers must be FQDNs and typically use the naming convention “ns1.example.com” and “ns2.example.com“.

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