DNS is most commonly associated with the Internet. However, private networks use DNS extensively to resolve computer names and to locate computers within their local networks and the Internet. DNS provides the following benefits:
For more information about DNS, see RFC 1034 and RFC 1035. To read the text of these RFCs, use your Web browser to search for "RFC 1034" and "RFC 1035."
The domain namespace is the naming scheme that provides the hierarchical structure for the DNS database. Each node, referred to as a domain, represents a partition of the DNS database.
The DNS database is indexed by name, so each domain must have a name. As you add domains to the hierarchy, the name of the parent domain is added to its child domain (called a subdomain). Consequently, a domain's name identifies its position in the hierarchy. For example, in Figure 5.1, the domain name sales.microsoft.com identifies the sales domain as a subdomain of the microsoft.com domain and microsoft as a subdomain of the com domain.
The hierarchical structure of the domain namespace consists of a root domain, top-level domains, second-level domains, and host names.
The term domain, in the context of DNS, is not related to the term as used in the Windows 2000 directory services. A Windows 2000 domain is a grouping of computers and devices that are administered as a unit.
Figure 5.1 Hierarchical structure of a domain namespace
The root domain is at the top of the hierarchy and is represented as a period (.). The Internet root domain is managed by several organizations, including Network Solutions, Inc.
Top-level domains are two- or three-character name codes. Top-level domains are grouped by organization type or geographic location. Table 5.1 provides some examples of top-level domain names.
Table 5.1 Top-Level Domains
Country code of Australia
Top-level domains can contain second-level domains and host names.
Organizations such as Network Solutions, Inc., assign and register second-level domains to individuals and organizations for the Internet. A second-level name has two name parts: a top-level name and a unique second-level name. Table 5.2 provides some examples of second-level domains.
Table 5.2 Second-Level Domains
United States Department of Education
World Wide Web Consortium
Prime Minister of Australia
Host names refer to specific computers on the Internet or a private network. For example, in Figure 5.1, Computer1 is a host name. 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. In Figure 5.1, Computer1.sales.microsoft.com. (including the end period, which represents the root domain) is an FQDN.
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. By default, TCP/IP setup uses the computer name for the host name, replacing illegal characters, such as the underscore (_), with a hyphen (-). For accepted domain naming conventions, see RFC 1035.
When you create a domain namespace, consider the following domain guidelines and standard naming conventions:
Use Unicode characters only if all servers running the DNS Service in your environment support Unicode. For more information about the Unicode character set, read RFC 2044 by searching for "RFC 2044" with your Web browser.
A zone represents a discrete portion of the domain namespace. Zones provide a way to partition the domain namespace into manageable sections and they provide the following functions:
For more information about contiguous namespaces, see Lesson 6, "Understanding Active Directory Concepts," later in this chapter.
Figure 5.2 Domain namespace divided into zones
The name-to-IP address mappings for a zone are stored in the zone database file. Each zone is anchored to a specific domain, referred to as the zone's root domain. The zone database file does not necessarily contain information for all subdomains of the zone's root domain, only those subdomains within the zone.
In Figure 5.2, the root domain for Zone1 is microsoft.com, and its zone file contains the name-to-IP address mappings for the microsoft and sales domains. The root domain for Zone2 is development, and its zone file contains the name-to-IP address mappings only for the development domain. The zone file for Zone1 does not contain the name-to-IP address mappings for the development domain, although development is a subdomain of the microsoft domain.
A DNS name server stores the zone database file. Name servers can store data for one zone or multiple zones. A name server is said to have authority for the domain name space that the zone encompasses.
One name server contains the master zone database file, referred to as the primary zone database file, for the specified zone. As a result, there must be at least one name server for a zone. Changes to a zone, such as adding domains or hosts, are performed on the server that contains the primary zone database file.
Multiple name servers act as a backup to the name server containing the primary zone database file. Multiple name servers provide the following advantages:
Here are some questions to help you determine whether you have learned enough to move on to the next lesson. If you have difficulty answering these questions, review the material in this lesson before beginning the next lesson. The answers for these questions are in Appendix A, "Questions and Answers."