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228 Chapter 17. Berkeley Internet Name Domain (BIND)

17.2.2.1. Zone File Directives

Directives are identiﬁed by the leading $ character before the name of the directive and usually placed

at the top of the zone ﬁle.

The following directives are the most commonly used:

• $INCLUDE — Tells named to include another zone ﬁle in this zone ﬁle at the place where the

directive is used. This allows additional zone settings to be stored apart from the main zone ﬁle.

• $ORIGIN — Sets the domain name to be appended to any unqualiﬁed records, such as those that

only specify the host and nothing more.

For example, a zone ﬁle may contains the following line:

$ORIGIN domain.com

At this point, any names that are used in resource records and do not end in a trailing dot (.) will

have this domain name added to them. So, in other words, when the zone record is read by the

nameserver, the ﬁrst line below will be interpreted as the second line:

ftp IN CNAME server1

ftp.domain.com. IN CNAME server1.domain.com.

Note

The use of the $ORIGIN directive is unnecessary if you name the zone in /etc/named.conf the

same as the value you would assign to $ORIGIN. The zone’s name is used as the $ORIGIN direc-

tive’s value by default.

• $TTL — Sets the default Time to Live (TTL) value for the zone. This is the number, in seconds,

given to nameservers that tells how long the zone’s resource records should continue to be valid. A

resource record can contains its own TTL value, which would override this directive.

Increasing this value tells remote nameservers to cache this zone’s information for a longer time.

This reduces the number of queries made concerning this zone, but it also lengthens the amount of

time required to proliferate resource record changes.

17.2.2.2. Zone File Resource Records

Zone ﬁle resource records contain columns of data, separated by whitespace, that deﬁne the record.

All zone ﬁle resource records are assigned a particular type, which designates the record’s purpose.

The following types of resource records are the most commonly used:

• A — Address record, which speciﬁes an IP address to assign to a name.

host IN A IP-address

Figure 17-7. Sample A record conﬁguration

If the host value is omitted, then an A record points to a default IP address for the top of the

namespace. This system will be the target of all non-FQDN requests.

Consider the following A record examples for the domain.com zone ﬁle:

1 2 ... 223 224 225 226 227 228 229 230 231 232 233 ... 281 282

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 228