What is an FQDN and how is it struc­tured?

The term “Fully Qualified Domain Name” (FQDN) refers to the complete and unique address of an online presence. It consists of a hostname and domain and is used to identify specific hosts on the internet and access them through name res­o­lu­tion.

FQDN meaning

FQDN stands for Fully Qualified Domain Name and describes the complete internet address used to uniquely identify an online presence. “Fully qualified” means that all domain levels are specified, allowing the address to be uniquely iden­ti­fied. An FQDN consists of the hostname and the domain, including the top-level domain (TLD), and can be uniquely mapped to an IP address.

FQDN structure

A Fully Qualified Domain Name is made up of several labels, including the hostname, domain name, any optional sub­do­mains and the top-level domain. If not all labels needed for a complete FQDN are specified, the result is known as a Partially Qualified Domain Name (PQDN). This often means that only the hostname is given. The term Fully Qualified Host Name (FQHN) is also sometimes used to refer col­lec­tive­ly to an FQDN and its as­so­ci­at­ed IP address.

To better un­der­stand the hierarchy of an FQDN, it helps to read its structure from right to left. The further to the right a label appears, the higher its position in the hierarchy:

• Root label: At the highest level is the root label, also known as the null label. It rep­re­sents the root of the Domain Name System (DNS) and consists of an empty label rep­re­sent­ed by a dot. In modern browsers, this final dot usually does not need to be entered ex­plic­it­ly.
• Top-level domain: The next level is the top-level domain, such as .org, .com or .net.
• Domain: Below the top-level domain is the domain name. During name res­o­lu­tion, the DNS hierarchy is followed from the TLD to the cor­re­spond­ing domain.
• Hostname: At the lowest level is the hostname, which iden­ti­fies the specific host within the domain.

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How to find FQDN in Windows

In Windows 11, you can find your computer’s FQDN under “Full computer name.” Enter “Settings” in the Windows search field, then select “System” > “About.” Under “Device spec­i­fi­ca­tions,” you will find the full computer name, which consists of the computer name (hostname) and the domain. If the computer is not connected to a domain, only the local hostname is displayed.

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In Windows 10, the process is similar. Enter Control Panel in the Windows search field, then select System and Security > System. Near the bottom of the page, you will find the full computer name of your device, which consists of the computer name (hostname) and the domain. If the computer is not connected to a domain, only the local hostname is displayed.

In Windows 7, you can access this in­for­ma­tion by right-clicking Computer in the Start menu and selecting Prop­er­ties.

You can also display the FQDN in Windows using the command line. Enter the following command and press Enter:

echo %COMPUTERNAME%.%USERDNSDOMAIN%

The FQDN will then be displayed. If your computer is not connected to a domain, the unchanged %USERDNSDOMAIN% variable will appear after the computer name.

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How to find FQDN in macOS

If your computer is connected to a domain, you can display the FQDN of your macOS device by entering the following line in the terminal and con­firm­ing with the Enter key:

hostname -f

How to find FQDN in Linux

In Linux, you can use the same command in the terminal as on macOS:

hostname -f

Al­ter­na­tive­ly, you can also use the following command:

hostname --fqdn

After pressing the Enter key, your FQDN will then be displayed. If you are not connected to a domain, only the hostname will be shown.

FQDN explained with an example

The following FQDN example il­lus­trates the structure of a Fully Qualified Domain Name (FQDN):

Example: www.ionos.com

• Hostname: www
• Domain: ionos
• TLD (Top-Level Domain): .com
• Root: The dot (.) at the end, which rep­re­sents the root label

Extension with sub­do­mains

Between the second-level domain and the hostname, sub­do­mains can be inserted that represent sub­sec­tions of the domain, such as shop or blog. Ad­di­tion­al sub­do­mains can be referred to as third-level domain, fourth-level domain, and so on.

Example: Fic­ti­tious FQDN hosting.example.IONOS.com

• example is a subdomain of IONOS.com.
• hosting is the hostname that des­ig­nates the specific server.

The number of sub­do­mains is limited only by the maximum length of the FQDN (255 char­ac­ters).

Why FQDNs are essential for network com­mu­ni­ca­tion

A Fully Qualified Domain Name is an essential part of the internet, allowing hosts to be uniquely iden­ti­fied and ensuring accurate name res­o­lu­tion. Its structure, con­sist­ing of the hostname, domain and top-level domain, enables reliable nav­i­ga­tion and com­mu­ni­ca­tion across networks.

You can find the FQDN of your own computer using the methods described for Windows, macOS or Linux. Knowing the FQDN can be useful for network con­fig­u­ra­tion, trou­bleshoot­ing and iden­ti­fy­ing devices within a network.