A fully qualified domain name (FQDN) gives a host’s complete location in the DNS hierarchy. Its labels are separated by dots, allowing the name to identify the host globally. For example, www.google.com names the www host in the google.com domain. section 3.1.3
Distinguish an FQDN from a partially qualified domain name (PQDN):
- The trailing dot in www.google.com. delimits the top-level domain from the unnamed root; it is commonly omitted in ordinary use. section 3.1.3 section 3.3
- A name such as www can identify a host only within its local domain, so it is a PQDN rather than a globally identifying name. section 3.1.3
- DNS names are case-insensitive, although lowercase spelling is standard. section 3.1.3
Reading a complete DNS name
In www.business.com, www is the hostname, business.com identifies its domain hierarchy, and the complete name identifies that host globally. The same hostname alone could refer to many different hosts in other domains. section 3.1.3
