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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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