Configuring and Managing MPE/iX Internet Services (August 2002)

Chapter 8
DNS BIND/iX
Explanation of Terms
119
• dnsquery — give all the DNS details and Mail exchange records
Explanation of Terms
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.