Section 3.4: Domain Name Space
The DNS database hierarchical naming scheme called a domain name space. Each node in the name space hierarchy represents a partition of the DNS database. These nodes are referred to as domains, each of which must have a name as the DNS database is indexed by name. When you add domains to the hierarchy, the name of the parent domain is appended to the domain, which becomes a child domain or a subdomain. Consequently, a domain's name identifies its position in the hierarchy. Thus, the studyguides.testking.com domain name identifies the studyguides domain as a subdomain of the testking.com domain and testking as a subdomain of the com domain.
Note: The term domain, in the context of DNS, is not related to domain as used in the Microsoft Windows Server 2003 directory services. A Windows Server 2003 domain is a grouping of computers and devices that are administered as a unit.
The hierarchical structure of the domain name space consists of a root domain, top-level domains, second-level domains, any subdomains, and host names.
• The Root Domain is at the top of the hierarchy and is represented as a period (.).
• Top-Level Domains are two or three-character name codes. Top-level domains are organized by organization type or geographic location. Table 3.1 provides some examples of top-level domain names.
Table 3.1: Top-Level Domains
|
Top-level Domain |
Description |
|---|---|
|
gov |
Government organizations |
|
com |
Commercial organizations |
|
edu |
Educational institutions |
|
org |
Noncommercial organizations |
|
cn |
Country code of China |
Top-level domains can contain second-level domains and host names.
• Second-Level Domains are registered to individuals and organizations for use on the Internet. A second-level name has two name parts: a top-level name and a unique second-level name. An example is testking. com.
• Subdomains are created when organizations extend their DNS tree to represent departments, divisions, or other geographic locations. Subdomains have three name parts: a top-level name, a unique second-level name, and a unique name representing the department or location. An example is studyguides. testking. com.
• Host names are the names of specific computers on the Internet or in a private network. A host name is the leftmost portion of a fully qualified domain name (FQDN), which describes the exact position of a host within the domain hierarchy. Computer1.studyguides.testking.com. is an FQDN and includes the end period. DNS uses a host's FQDN to resolve a name to an IP address. The host name does not have to be the same as the computer name.