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What does FQDN stand for?
Author:
HOSTTEST Editorial
| 27 Jan 2022
The abbreviation FQDN stands for the term Fully Qualified Domain Name. The acronym represents the complete domain name of an internet presence or a host.
To ensure completeness, all domain levels such as Top Level Domain, Subdomain, and Hostname are included in the Fully Qualified Domain Name. This makes the domain name system completely unique. Consequently, each associated IP address of a nameserver can be easily assigned to the DNS (Domain Name System) via the resource records. In contrast to FQDN, domain names that do not list all domain levels are referred to as PQDN (Partially-Qualified Domain Name).
Fully Qualified Domain Name - the Position in DNS
The Fully Qualified Domain Name (FQDN) refers to the complete hierarchy of an internet presence within the Domain Name System (DNS), including the full domain name for a host. This includes the Root Level, Top Level Domain, all relevant Subdomains, and Hostnames. The different domain levels are separated by dots, with experts referring to these areas as labels. The Root Label represents the highest level in the hierarchy, typically consisting of an empty field. Therefore, the FQDN ends with a dot after the Top Level Domain. Depending on the application and requirements, this dot may be omitted under certain conditions.
The Identity of the FQDN
The Fully Qualified Domain Name is always uniquely identifiable. Mapping to an IP address can be achieved using A or AAAA records from a nameserver. Suitable are associated IPv4 or IPv6 addresses. Some experts use the acronym FQHN (Fully Qualified Host Name) in RFCs as a generic term for FQDN and IP address. However, if individual labels are missing within the domain name, the expert considers it a Partially Qualified Domain Name, abbreviated as PQDN.
Syntax and Structure
A predefined syntax forms the basis for the Fully Qualified Domain Name. The hierarchy of the Domain Name System (DNS) is represented in individual labels that denote the various hierarchy levels, separated by dots.
To better understand the naming hierarchy in the FQDN, it makes sense to view the structure from right to left. In the hierarchy representation, labels that are further right are higher than those further left.
The highest level is held by the Root Label or Null Label, representing the "root" in the Domain Name System. This label consists of an empty space, displayed only by a dot, which no longer needs to be manually entered in modern browsers.
The Top-Level Domain is in the subsequent level of the hierarchy, named with "de", "net", or "com", for example.
The directory of the specified TLD is searched to find the domain of the lower hierarchy level and thus resolve the address of the nameserver.
Once the IP address of the nameserver has been identified, the hostname located in the lowest label can now be contacted, and the specified page can be accessed.
Example of a Fully Qualified Domain Name
For example, server1.example-domain.de represents a FQDN as [Hostname].[Domain].[TLD].[Root]. The right dot in the name is always included in the directory of nameservers. However, the Root label after this dot remains empty. The Top-Level Domain (TLD) in this example is ".de", which stands for Germany. Country-specific Top-Level Domains are grouped under the abbreviation ccTLD (Country code top-level domain). Top-Level Domains like ".org" or ".com" are known as generic Top-Level Domains. Following the Top-Level Domain is the actual domain name, also known as the Second-Level Domain or Second-Level Label. In this example, the domain name is "example-domain". On the far left is the hostname or the Third-Level Label. In this case, the hostname is "server1".
There is enough space between the hostname and the Second-Level Domain to insert subdomains. A subdomain refers to a subsection of the domain. Multiple subdomains can appear in succession here. The number of subdomains is limited only by the maximum total length that a Fully Qualified Domain Name can reach.
Restrictions on FQDN Allocation
When creating a Fully Qualified Domain Name, attention must be paid to the number of characters. Each individual label may contain a maximum of 63 characters. The complete Fully Qualified Domain Name must not exceed a total length of 255 characters. Numbers and hyphens are also allowed as characters. However, a label must not start with a hyphen. The total sum of characters is calculated from the letters, numbers, and hyphen.
When to Use a Fully Qualified Domain Name?
If you aim for perfect recognition and accessibility of your online presence, you can use FQDN to uniquely name an internet resource like the host. Of course, a valid IPv4 or IPv6 address must be assigned to the Fully Qualified Domain Name. Otherwise, communication on the internet would not be possible. Only so-called A or AAAA records on a nameserver make this possible. These entries, known as Resource Records, link an IP address to the FQDN. Additionally, the addressing of IP packets with the IP address of the desired target is authorised.
Finding FQDN in Windows
In Windows, the Fully Qualified Domain Name is listed under the name "Full Computer Name." To locate the FQDN in Windows 10, type "Control Panel" into the search field. From there, click on "System and Security," and then select "System." At the end of this page, you will find the full computer name of the respective device. This consists of the hostname also provided there and the domain. However, only the local hostname is displayed here unless the computer is explicitly connected to a domain.
Working with FQDN
For numerous applications, a Fully Qualified Domain Name can be useful. Among other things, specifying FQDN may be necessary to issue an SSL certificate for the server. Contacting a web server via a web browser is controlled by entering the FQDN in the browser address bar. In this application, specifying the final period for the root label behind the Top Level Domain is not necessary.
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