Red Hat LINUX 7.2 Reference Manual page 224

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14.1.1 Zones
On the Internet, the FQDN of a host can be broken down into different sections, and these sections are
organized in a hierarchy much like a tree, with a main trunk, primary branches, secondary branches,
and so forth. Consider the following FQDN:
Figure 14–1 Example of a fully qualified domain name
bill.sales.domain.com
When looking at how a FQDN is resolved to find the IP address that relates to a particular system,
you must read the name from right to left, with each level of the hierarchy divided by dots (.). In this
example, the com defines the top level domain for this FQDN. The domain name is a sub-domain
under com, with sales as a sub-domain under domain. The name furthest left in a FQDN is the
hostname, identifying a particular machine.
Except for the hostname, every section is a called a zone, which defines a particular namespace. A
namespace controls the naming of the sub-domains to its left. While this example only contains two
sub-domains, a FQDN must contain at least one sub-domain but may include many more, depending
upon the namespace organization in use.
Zones are defined on authoritative nameservers through the use of zone files, which describe the
namespace of that zone, the mail servers to be used for a particular domain or sub-domain, and much
more. Zone files are stored on primary nameservers (also called master nameservers), which are
truly authoritative and where changes are made to the files, and secondary nameservers (also called
slave nameservers), which receive their zone files from the primary nameservers. Any nameserver
can be a primary and secondary nameserver for different zones at the same time, and they may also
be considered authoritative for multiple zones. It all depends on the nameserver's particular configu-
ration..
14.1.2 Types of Nameservers
There are four primary nameserver configuration types:
• master — Stores original and authoritative zone records for a certain namespace, answering ques-
tions from other nameservers searching for answers concerning that namespace.
• slave — Also answers queries from other nameservers concerning namespaces for which it is
considered an authority. However, slave nameservers get their namespace information from mas-
ter nameservers via a zone transfer, where the slave sends the master a NOTIFY request for a
particular zone and the master responds with the information, if the slave is authorized to receive
the transfer.
• caching-only — Offers name to IP resolution services but is not authoritative for any zones. An-
swers for all resolutions are usually cached in a database stored in memory for a fixed period of
Chapter 14:Berkeley Internet Name Domain (BIND)