Book Image

DNS in Action

By : CP Books a.s.
Book Image

DNS in Action

By: CP Books a.s.

Overview of this book

The Domain Name System is one of the foundations of the internet. It is the system that allows the translation of human-readable domain names into machines-readable IP addresses and the reverse translation of IP addresses into domain names. This book describes the basic DNS protocol and its extensions; DNS delegation and registration, including for reverse domains; using DNS servers in networks that are not connected to the internet; and using DNS servers on firewall machines. Many detailed examples are used throughout the book to show perform various configuration and administration tasks.
Table of Contents (16 chapters)
DNS in Action
About the Authors
Country Codes and RIRs

1.5 Zone

We often come across the questions: What is a zone? What is the relation between a domain and a zone? Let us explain the relationship of these terms using the domain.

As we have already said, a domain is a group of computers that share a common right side of their domain name. For example, a domain is a group of computers whose names end with However, the domain is large. It is further divided into the subdomains,,,, etc. We can administer the entire domain on one name server, or we can create independent name servers for some subdomains. (In Figure 1.3, we have created subordinate name servers for the subdomains and The original name server serves the domain and the subdomains,, and—in other words, the original name server administers the zone. The zone is a part of the domain namespace that is administered by a particular name server.

Figure 1.3: Zone

A zone containing data of a lower-level domain is usually called a subordinate zone.

1.5.1 Special Zones

Besides classic zones, which contain data about parts of the domains or subdomains, special zones are also used for DNS implementation. Specifically, the following zones are used:

  • Zone stub: Zone stub is actually a subordinate zone that only contains information about what name servers administer in a particular subdomain (they contain the NS records for the zone). The zone stub therefore does not contain the entire zone.

  • Zone cache/hint: A zone hint contains a list of root name servers (non-authoritative data read into memory during the start of the name server). Only BIND version 8 and later use the name hint for this type of zone. In previous versions, a name cache zone was used. Remember that the root name servers are an authority for a root domain marked as a dot (.).