Chapter 16.

Berkeley Internet Name Domain (BIND)

Today, the Internet and almost all local networks depend upon a working and reliable Domain Name

Service (DNS), which is used to resolve names of systems into IP addresses and vice versa.

In order to facilitate DNS on your network, a nameserver is required to translate these names into the

IP addresses necessary to make the connection. In addition, a nameserver can translate IP addresses

back into a system's name, commonly called a reverse lookup.

This chapter discusses BIND, the structure of its configuration files, and how it may be locally or

remotely administered.

For instructions on configuring BIND using the graphical Bind Configuration Tool

(

redhat config bind

), please see the chapter called BIND Configuration in the Official Red Hat

Linux Customization Guide.

Warning

If you use the Bind Configuration Tool, you should not manually edit any BIND configuration files

because all changes will be overwritten the next time you use the Bind Configuration Tool.

16.1. Introduction to DNS and BIND

Systems using IP networks must know the IP address of a remote machine in order to connect to

it. However, most users prefer to use the name of a machine, called a hostname or a fully qualified

domain name (FQDN), when connecting to it.

Use of fully qualified domain names also have advantages for system administrators. They allow

administrators to flexibility in changing the IP addresses for individual machines without effecting

name based queries to the machines. Conversely, administrators can shuffle which machines handle a

name based query in a way transparent to the user.

The service that facilitates this is caused DNS, and it is normally implemented using centralized

servers that are authoritative for some domains and refer to other DNS servers for other domains.

DNS under Linux is made possible through the use of a nameserver daemon that performs the

IP/hostname translation. A client application will request information from the nameserver, usually

connecting to it on the server's port 53. The nameserver will attempt to resolve the FQDN based on

its resolver library, which may contain authoritative information about the host requested or cached

data about that name from an earlier query. If the nameserver does not already have the answer in

its resolver library, it will turn to other nameservers, called root nameservers, to determine which

nameservers are authoritative for the FQDN in question. Then, with that information, it will query the

authoritative nameservers for that name to determine the IP address. If performing a reverse lookup,

the same procedure is used, except the query is made with an unknown IP address rather than a name.

16.1.1. 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:

bill.sales.domain.com