A host name is a name that is assigned to a host (i.e., a computer connected to the network) that uniquely identifies it on a LAN (local area network) and thus allows it to be addressed locally without using its full IP address.
A domain name is a name that uniquely identifies a site (e.g., web site or ftp site) on the Internet or other TCP/IP (transmission control protocol/Internet protocol) network. A TLD is a suffix on a domain name such as .com or .org as well as a country code if used (e.g., .uk or .fr). Domain names inclusive of their TLDs are actually user-friendly substitutes for IP addresses, which form the basis for addressing on the Internet and other TCP/IP networks and which can consist of up to 12 digits.
If the host name in the above example were ftp, then the FQDN would be ftp.bellevuelinux.org, and if it were support, then the FQDN would be support.bellevuelinux.org. If the domain name had been set up so that the country code TLD (ccTLD), in this case .us, were also required, then the FQDNs would be ftp.bellevuelinux.org.us and support.bellevuelinux.org.us, respectively.
A FQDN is not the same as a URL (universal resource locator), but rather it is a part of it. This is because a FQDN lacks the TCP/IP protocol name (e.g., http or ftp) that is always used at the start of a URL. Moreover, a URL can also include a directory path, a file name and a TCP port number.
Sometimes FQDNs are provided instead of the full URLs as addresses for resources on the Internet, and thus no TCP/IP protocol name is specified. In such case the protocol is assumed by default to be HTTP (hypertext transfer protocol).
The process of converting FQDNs to IP addresses is carried out by the domain name system (DNS) and is called name resolution.
Created December 7, 2005.