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Fully Qualified Domain Name - FQDN

The Fully Qualified Domain Name (FQDN) is the complete and unique name of a computer or host on the internet or a local network. It consists of multiple parts that reflect a hierarchical structure.

Structure of an FQDN

An FQDN is made up of three main components:

  1. Hostname – The specific name of a computer or service (e.g., www).

  2. Domain Name – The name of the higher-level domain (e.g., example).

  3. Top-Level Domain (TLD) – The highest level of the domain structure (e.g., .com).

Example of an FQDN:
👉 www.example.com.

  • www → Hostname

  • example → Domain name

  • .com → Top-Level Domain

  • The trailing dot (.) is optional and represents the root domain of the DNS system.

Why is the FQDN important?

Uniqueness: Each FQDN is globally unique and refers to a specific resource on the internet.
DNS Resolution: It is used by DNS servers to find the IP address of websites and servers.
SSL Certificates: An FQDN is often required for SSL/TLS certificates to ensure secure connections.
Email Delivery: Mail servers use FQDNs to send emails to the correct hosts.

Difference Between an FQDN and a Simple Domain

  • FQDN: mail.google.com (fully specified)

  • Simple Domain: google.com (can contain multiple hosts, e.g., www, mail, ftp)

In summary, the FQDN is the complete address of a device or service on the internet, while a simple domain is a more general address.