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 prepended to the name of the Internet hierarchy to which it belongs. For example, the ajax domain shown in Figure 27-4has been registered as part of the Internet com hierarchy. Therefore, its Internet domain name becomes ajax.com.

Figure 27-6 shows the position of the ajax.com domain in the DNS namespace on the Internet.

Figure 27-6 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 does not require domain names to be capitalized, though they may be. Here are some examples of machines and domain names:

Boss.manf.ajax.com
 quota.Sales.ajax.com

The Internet organization regulates administration of its domains by granting each domain authority over the names of its hosts and by expecting each domain to delegate authority to the levels below it. Thus, the com domain has authority over the names of the hosts in its domain. It also authorizes the formation of the Ajax.com domain and delegates authority over the names in that domain. The Ajax.com domain, in turn, assigns names to the hosts in its domain and approves the formation of the Sales.Ajax.com, Test.Ajax.com, and Manf.Ajax.com domains.

Fully-Qualified Domain Names

A domain name is said to be fully-qualified when it 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 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 the name.