Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual page 240

Chapter 17. Berkeley Internet Name Domain (BIND)
server1 IN A 10.0.1.5
www IN CNAME server1
MX
This refers to the Mail eXchange record, which tells where mail sent to a particular namespace
controlled by this zone should go.
IN MX <preference-value><email-server-name>
Here, the <preference-value> allows numerical ranking of the email servers for a namespace,
giving preference to some email systems over others. The MX resource record with the lowest
<preference-value> is preferred over the others. However, multiple email servers can
possess the same value to distribute email traffic evenly among them.
The <email-server-name> may be a hostname or FQDN.
IN MX 10
IN MX 20
In this example, the first mail.example.com email server is preferred to the
mail2.example.com email server when receiving email destined for the example.com domain.
NS
This refers to the NameServer record, which announces the authoritative nameservers for a
particular zone.
The following illustrates the layout of an NS record:
IN NS <nameserver-name>
Here, <nameserver-name> should be an FQDN.
Next, two nameservers are listed as authoritative for the domain. It is not important whether these
nameservers are slaves or if one is a master; they are both still considered authoritative.
IN NS dns1.example.com.
IN NS dns2.example.com.
PTR
This refers to the PoinTeR record, which is designed to point to another part of the namespace.
PTR records are primarily used for reverse name resolution, as they point IP addresses back
to a particular name. Refer to
examples of PTR records in use.
SOA
This refers to the Start Of Authority resource record, which proclaims important authoritative
information about a namespace to the nameserver.
Located after the directives, an SOA resource record is the first resource record in a zone file.
The following shows the basic structure of an SOA resource record:
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mail.example.com.
mail2.example.com.
Section 17.3.4, "Reverse Name Resolution Zone Files"
for more