Fully Qualified Domain Names (FQDN): What are they and why do we use them?

6 Oct 2017 / Aliesha Ellington

All websites will either have a Fully Qualified Domain Name (FQDN) or a Partially Qualified one (PQDN). Not all sites show the full credentials within their domain name. Let’s first look at what a Fully Qualified Domain is. Then explore how to find a website’s full domain name, and why you may need to know this information.

There is But One

 It is the full representation of a computer, or host. There is only one way to write a Fully Qualified Domain Name. The FQDN is made up of multiple different parts, separated by a full stop. It is made up of components falling under the categories of ‘domain name’ and ‘host name’.

 FQDN all use the same format (hostname).(domain).(TLD). The domain may contain a sub domain as well. An FQDN is read from the right side to the left, root to host.

If we look at www.freeparking.co.nz reading right to left, the first thing we interpret is the Top Level Domain (TLD) which in this case is (.co.nz), next is (freeparking) which is the second level domain, also known as the domain name. Thirdly the (www) which is the host, the world wide web.

WWW is not the only host name that can be used. You will often see things such as ftp (ftp.domain.net) or mail (mail.google.com), these represent a protocol or service. A lot of websites now choose to leave out the host (www) from the beginning of their URL’s, therefore they are only Partially Qualified, not Fully Qualified Domain names.

FQDN’s actually contain an empty element, an extra dot at the end of the TLD. For example www.freeparking.co.nz. Which is removed/hidden by most internet browsers as it’s not deemed necessary, it basically just represents the internet in general. To say that the entire site is hosted on the internet.

An FQDN is like an address, with GPS co-ordinates of exactly where it is within the Domain Name System (DNS). It means that each computer, or server, has it’s own personal identifier and can be located within the internet’s framework. The DNS is like the internet’s address book, it locates domain names and then translates them into IP addresses. A Partially Qualified Domain Name only gives general not complete information about the location in the internet or within a private server, an incomplete entry into the address book.  A Fully Qualified one provides the exact location within the DNS, which we can then access.

How to Search for A FQDN

This varies slightly by Operating System, so we have provided the most common three, with instructions on how to find the FQDN of your server or computer.

MAC OS.Open the terminal. Type “hostname_f” into the prompt. The Terminal will then provide you with the FQDN.

Windows 10.Go to the ‘Search Windows’ box within the Taskbar, and type in ‘control panel’. Then click ‘systems and security’, then click on ‘system’ and you will see the FQDN next to the Full Computer Name label.

Linux.Go to the terminal and type in “hostname_A” into the prompt. Bear in mind the A must be a capital, it is case sensitive. The terminal will then provide you with the FQDN.

Once you have discovered your FQDN you are then able to make your device available online to others, through the DNS.

FQDN’s and their Many Uses

Defining a FQDN locally is not sufficient enough to bring it online. You will need to go into the DNS settings and update the records there in order for the DNS to recognise and know the exact location of your specific device. By defining the DNS namespaces, this allows the DNS to connect your FQDN to IPs and be able to locate your device on the internet.

If you would like more information on what the DNS is, and how it works, this article explains it wellhere.

There are a range of uses for a FQDN, here are a few of the commonly used ones:

  • For Obtaining a Secure Sockets Layer, or SSL,certificate. This creates a secure connection between the client and the server.
  • For Remotely Connecting to a Host. The DNS uses the FQDN to find the server, when connecting to a virtual machine or remote host.
  • For Accessing Particular Domain Services or Protocols. If you are connecting to an FTP or email server you will need to know it’s FQDN, because any activity which transfers information across a network uses the process of the DNS, to search for the exact information to be transferred, and the exact location to transfer it to. For example when setting up your email account for the first time on a new phone or computer, you will generally need to know the FQDN of the email server.

In conclusion, a FQDN is a full address, like GPS co-ordinates, helping the DNS find a specific location. We use FQDN’s surprisingly often in our day to day interactions with the internet. Why not try and search for your computer’s FQDN yourself, or share this new knowledge casually in conversation to impress your colleagues.  


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