What is FQDN?

Fully Qualified Domain Name, or for short FQDN, presents exactly the complete name of a specific domain name. Moreover, that applies to servers too and not only to websites. The Domain Name System (DNS) is built and organized hierarchy. It begins from the top level that is the root, followed by the TLD, a level below is the domain, and finally, the last level is the particular hostname.

To make things simple, let’s see the complete syntax of a fully qualified domain name (FQDN):

hostname. domain name. TLD 

([hostname].[domain].[tld].)

Here are some examples of a fully qualified domain name that you probably have seen:

mail.google.com. 

ftp.microsoft.com. 

movies.disney.com.

Keep in mind that the dot “.” that is last in the syntax is commonly neglected. It simply represents the root level. Typically the FQDN ends with the TLD. Yet, there are some cases where that dot is required, and you are going to need to add it. Also, it depends on the software you are currently applying.

With a Fully Qualified Domain Name, you are able to see where exactly an object exists in the hierarchy of the Domain Name System.

Components 

The Fully Qualified Domain Name has 3 main components. They are the following: 

  • The first component is the TLD (Top Level Domain) – It is described with the extension in the end that you can view in an FQDN. Usually it includes 2 or 3 letters, for instance .com, .eu, .net etc.
  • The second component is the subdomain – You can see it as the domain one level below the Top Level Domain (TLD). For illustration, domain.com.
  • The third component is the hostname – It is described with the signs located at the start of the Fully Qualified Domain Name. A simple and very familiar example is www in www.domain.com. The domain owner could create various hostnames as they are connected with a subdomain. For illustration:
    • mail.domain.com
    • www.domain.com
    • ftp.domain.com

Use cases of FQDN

  1. If you want to get an SSL Certificate – Almost every site has one, and you need to provide the FQDN to receive it.
  2. If you want to connect to a host remotely – The Fully Qualified Domain Name is a requirement when you want to connect to a remote host. That means that it isn’t local to your ISP.
  3. If you want to access a specific Domain Service or Protocol – The FQDN is required, for instance, when you want to establish email for particular applications.

What is PQDN (Partially Qualified Domain Name)?

The Partially Qualified Domain Name, or for short PQDN, is a Fully Qualified Domain Name, simply with an absent part. It does not contain all of the components, which give the exact position on the DNS hierarchy. To make things more simple, for instance, a PQDN is google.com. The reason for that is there is an absent web host (www.) before the domain name. 

Everyday users usually apply PQDN because it is more accessible and easy. Besides, it is shorter, which makes PQDN more simple to use.