A complete domain name is known as a fully qualified domain name (FQDN). A FQDN states the exact position of a target computer within the tree hierarchy of the domain name system and is made up of two parts: the host name and the domain name. The following example is a fictitious mail server’s FQDN
mailserver.example.com.
While mailserver represents the host name, example.com indicates the domain where the specific computer can be found. For server host names responsible for operating websites, the typical www is used:
www.example.com.
Note that the fully qualified domain name is different to internet addresses in everyday use in that they end with a period. This is due to the hierarchical structure of the domain name system and as a result, domains are itemized starting from the highest level and ending with the root label.
Third-Level-Domain | | Second-Level-Domain | | Top-Level-Domain | | Root-Label |
---|
www | . | example | . | com | . | (empty) |
From right to left, the domain example structure is as follows: root label, top-level domain (TLD), second-level domain (SLD), and third-level domain. The FQND from www.example.com. even contains 4 sections. In principle, domains can contain further subdomains below the third-level domain.