Understanding FQDN with Examples
Updated: Oct 1
A Fully Qualified Domain Name (FQDN) is the complete domain name of a specific computer, or host, online. A FQDN gives its precise location in the hierarchy of DNS records. It is the complete address for websites and other computers and entities accessing the Internet resolving to the root domain.
An FQDN is comprised of several elements: a hostname and a domain name. These elements are separated by a period.
Example of an FQDN
The following example clarifies the structure of a fully qualified domain name:
In a name server’s directory, the dot on the far right is always included in the FQDN.
The "host" or "hostname" part is www
The "domain" part is howtouselinux.com
The FQDN is www.howtouselinux.com.
Here is another example of FQDN. Some clarifications about the terminology; consider this example: foo.example.com
The "host" or "hostname" part is foo
The "domain" part is example.com
The FQDN is foo.example.com
Structure of FQDN
The structure of an FQDN is predefined by the domain name system (DNS). The names of the individual levels in the domain name area are called “labels” and are separated from one another by dots. Each label must consist of 1 to 63 characters and the total FQDN may not exceed 255 characters in total. Only letters, numbers, or dashes can be used. Each label has to have either a letter or a number at the beginning.
The fully qualified domain name consists of three or more labels: The top level domain, the domain names, optional subdomains, and the host name. I
Take www.howtouselinux.com, for example. The first element and domain level of the FQDN is the top level domain (TLD), which, in this case, is “.com.” Within the TLD, howtouselinux is the assigned domain name/second-level domain. Lastly, “www.” is the hostname.
How to look up a FQDN?
Looking up the FQDN of our computer or server is simple. Just follow the instructions for our operating system below. If our machine does not provide the FQDN, it is not connected to a domain.
Windows 10. Within the taskbar’s “Search Windows” box, type “control panel” and select “system and security.” Next, select “system” and the FQDN is listed next to the Full Computer Name label.
Mac OS. Open terminal, and enter “hostname -f” into the prompt. Terminal will return the FQDN.
Linux. Open terminal and enter “hostname -A” into the prompt. The “A” is case sensitive. Terminal will return the FQDN.
Once we know our Fully Qualified Domain Name, we can make our device available online through the DNS.
More Information on FQDN
A Fully Qualified Domain Name designates the specific location of an object within the Domain Name System (DNS) hierarchy; it communicates the host’s position relative to the root of the DNS namespace.
An FQDN enables each entity connected to the internet (computer, server, etc.) to be uniquely identified and located within the internet framework.