Domain Names

Domain names indicate a domain's position in the overall DNS namespace, much as path names indicate a file's position in the UNIX file system. After your local domain is registered, its name is added to the name of the Internet hierarchy to which the domain belongs. For example, the ajax domain that is shown in Figure 3–5 has been registered as part of the Internet com hierarchy. Therefore, its Internet domain name becomes ajax.com.

The following figure shows the position of the ajax.com domain in the DNS namespace on the Internet.

Figure 3–5 Ajax Domain's Position in the DNS Namespace

The ajax.com subdomains now have the following names.

sales.ajax.com
test.ajax.com
manf.ajax.com

DNS domain names can be capitalized or in lower case. Here are some examples of machines and domain names.

boss.manf.ajax.com
quota.sales.ajax.com

The Internet organization grants each domain authority over the names of its hosts. The organization expects each domain to delegate authority to the levels below. Thus, the com domain has authority over the names of the hosts in its domain. The organization also authorizes the formation of the ajax.com domain and delegates authority over the names in that domain. The ajax.com domain then assigns names to the hosts in its domain. The ajax.com domain also approves the formation of the sales.ajax.com, test.ajax.com, and manf.ajax.com domains.

Fully Qualified Domain Names (FQDNs)

A domain name is said to be fully-qualified when the name includes the names of every DNS domain from the local domain on up to “.”, the DNS root domain. Conceptually, the fully qualified domain name indicates the path to the root, as does the absolute path name of a UNIX file. However, fully qualified domain names are read from lowest, on the left, to highest, on the right. Therefore, a fully-qualified domain name has the following syntax.

The fully qualified domain names for the ajax domain and its subdomains are:

ajax.com. 
sales.ajax.com. 
test.ajax.com. 
manf.ajax.com.

Note the dot at the furthest right position of each name.