What is a Fully Qualified Domain Name (FQDN)?

When working with domains and DNS management understanding what a FQDN is can be very helpful. This article will help explain the concept of a FQDN and a domains different components.

The Parts of a Domain

A domain is made up of a two essential parts, the Top-Level Domain (TLD) and the main Domain Name which is what you register. The other component of domain names are the subdomains.

  • DNS Root: A DNS zone that contains all Top-Level Domains
    • The DNS root is often designated by a ‘.’ following the TLD.
  • Top-Level Domain or TLD
    • For example: .com, .net, .org, and many more
  • Domain Name, or the domain you bought
  • Sub-domains

Interestingly, domains are actually interpreted by computers from right-to-left rather than left-to-right. This is done with good reason, the same ‘Domain name’ could be registered with multiple TLDs. By reading right-to-left this allows DNS resolution to be accurate and efficient. For example, when pulling up sxi.io, instead of asking for all possible ‘liquidweb’ domains your browser specifically asks the main ‘.com’ nameserver for the ‘liquidweb’ domain record.

So what exactly is a FQDN?

Now armed with knowledge of domain components understanding FQDN should be much easier.

A FQDN is simply a domain that includes all the necessary components to resolve an exact location. Often referred to as an absolute domain name.

So a FQDN is not simply liquidweb, nor is it just www; a FQDN is the complete domain name which resolves to the main, or ‘root’ domain. Generally this means that the domain will include the ‘root’, however this is not a requirement.

With that in mind the following are examples of FQDNs:

  • www.google.com – or – www.google.com.
  • sxi.io – or – sxi.io.
  • bing.co.uk – or – bing.co.uk.