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BIND, which stands for Berkeley Internet Name Domain, is the
most commonly used implementation of DNS.
DNS is essentially a distributed data base, with control of
the different elements of the data base maintained by individuals
responsible for the domain served by that DNS server. The data is
used by DNS servers to assist one host in identifying the location
of another host anywhere in the system, translating a host name
to its IP address, and visa versa.
The DNS distributed data base is much like a directory. It
is organized in an inverted tree fashion, much like the unix directory
structure, with the most inclusive node, or domain, at the top,
with multiple levels of sub-domain names below, until at the end
are the actual host names.
Information about each domain, specifying the sub-domains
or hosts below it, are maintained in the DNS data base files. The
convention is to call these files "db files" in
BIND 4.X, and "zone files" in BIND 8.x. These
files are made known to the respective DNS server through a configuration file,
named.conf. In earlier versions of BIND, it was called named.boot.
When fully formed, a host name is made up of a sequence of
labels separated by dots. When read from right to left, as DNS parses
it, it describes a path leading from the most inclusive domain in
its tree, through successively more local domains, until its own
host name is reached.
Using the full host domain name, this is how a DNS server
traverses the DNS data base, starting at the right-most, most inclusive
domain, following data maintained by the various DNS administrators
in their respective data files, until it finds the target host name,
and its IP address.
A domain name is also made up of a sequence of labels separated
by dots. Rather than describing a host, it describes a domain, under
which other sub-domains and/or hosts exist. It can be located in
the DNS data base by DNS servers the same way as was the host domain name.
Sometimes a particular DNS server will not manage an entire
domain. Rather, the domain will be broken up into pieces, called "zones".
Responsibility for these various zones is "delegated" to other
DNS servers, and their respective DNS administrators. So, in DNS configuration
files, instead of describing a domain for which it is responsible,
the more general term "zone" is used.
It is also common, in fact recommended, for a DNS Server to
have at least one "backup", another machine that
will respond to queries when the main server is down. The main server
is knows as the "master" and the backup as the "slave".
In previous versions of BIND, they were known as "primary" and "secondary".
The rest of this section concerns itself with only "leaf" DNS
servers, that is. servers that only serve hosts. These servers have
no domains under it, only hosts.
There are four types of db or zone files used by a DNS server,
each identified in the server's named.conf file:
zone.DOMAIN — provides name-to-address mapping zone.ADDR — provides address-to-name mapping zone.LOCAL — a zone.ADDR file that
provides loopback mapping zone.CACHE — a zone.DOMAIN file that
identifies root name servers; also known as the
"zone.hint" file.
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