11.1 Domains and Subdomains

The entire Internet is divided into domains, i.e., name groups that logically belong together. The domains specify whether the names belong to a particular company, country, and so forth. It is possible to create subgroups within a domain that are called subdomains. For example, it is possible to create department subdomains for a company domain. The domain name reflects a host’s membership in a group and subgroup. Each group has a name affiliated with it. The domain name of a host is composed from the individual group names. For example, the host named bob.company.com consists of a host named bob inside a subdomain called company, which is a subdomain of the domain com.

The domain name consists of strings separated by dots. The name is processed from left to right. The highest competent authority is the root domain expressed by a dot (.) on the very right (this dot is often left out). Top Level Domains (TLDs) are defined in the root domain. We have...