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222 Chapter 17. Berkeley Internet Name Domain (BIND)

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 consid-

ered authoritative for multiple zones. It all depends on the nameserver’s particular conﬁguration.

17.1.2. 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 con-

sidered an authority. However, slave nameservers get their namespace information from master

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

time, usually speciﬁed by the retrieved zone record, for quicker resolution for other DNS clients

after the ﬁrst resolution.

• forwarding — Forwards requests to a speciﬁc list of nameservers to be resolved. If none of the

speciﬁed nameservers can perform the resolution, the process stops and the resolution fails.

A nameserver may be one or more of these types. For example, a nameserver can be a master for some

zones, a slave for others, and only offer forwarding resolution.

17.1.3. BIND as a Nameserver

Red Hat Linux includes BIND, which is a very popular, powerful, open source nameserver. BIND

uses the named daemon to provide its name resolution services. All conﬁguration information for

BIND is kept in the /etc/named.conf ﬁle and its zone ﬁles are in the /var/named/ directory. The

structure and options for these various types of ﬁles can be found in Section 17.2.

BIND version 9 includes a utility called /usr/sbin/rndc to allow the administration of the running

named daemon. More information about rndc can be found in Section 17.3.

17.2. BIND Conﬁguration Files

The BIND nameserver named server uses the /etc/named.conf ﬁle for conﬁguration. All zone ﬁles

are placed in the /var/named/ directory.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 222