HP-UX Reference (11i v2 07/12) - 4 File Formats (vol 8)

n
named.conf(4) named.conf(4)
example.com.INMX10mail.example.com.
INMX10mail2.example.com.
INMX20mail.backup.org.
mail.example.com.INA10.0.0.1
mail2.example.com.INA10.0.0.2
For example:
Mail delivery will be attempted to mail.example.com and mail2.example.com (in any order), and if neither
of those succeed, delivery to mail.backup.org will be attempted.
Setting TTLs
The TTL of the RR field is a 32-bit integer represented in units of seconds, and is primarily used by
resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be dis-
carded. The following three types of TTL are currently used in a zone file.
SOA The last field in the SOA is the negative caching TTL. This controls how long other
servers will cache no-such-domain (NXDOMAIN) responses from you. The maximum
time for negative caching is 3 hours (3h).
$TTL The $TTL directive at the top of the zone file (before the SOA) gives a default TTL for
every RR without a specific TTL set.
RR TTLs Each RR can have a TTL as the second field in the RR, which will control how long
other servers can cache the it.
All of these TTLs default to units of seconds, though units can be explicitly specified, for example, 1h30m.
Inverse Mapping in IPv4
Reverse name resolution (that is, translation from IP address to name) is achieved by means of the in-
addr.arpa domain and PTR records. Entries in the in-addr.arpa domain are made in least-to-most
significant order, read left to right. This is the opposite order to the way IP addresses are usually written.
Thus, a machine with an IP address of 10.1.2.3 would have a corresponding in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose data field is the name of the
machine or, optionally, multiple PTR records if the machine has more than one name. For example, in the
[example.com]
domain:
$ORIGIN2.1.10.in-addr.arpa
3IN PTR foo.example.com.
Note: The $ORIGIN lines in the examples are for providing context to the examples only-they do not
necessarily appear in the actual usage. They are only used here to indicate that the example is relative to
the listed origin.
Other Zone File Directives
The Master File Format was initially defined in RFC 1035 and has subsequently been extended. While the
Master File Format itself is class independent all records in a Master File must be of the same class. Mas-
ter File Directives include $ORIGIN, $INCLUDE, and $TTL.
The $ORIGIN Directive
Syntax:
$ORIGIN
domain-name [comment]
$ORIGIN sets the domain name that will be appended to any unqualified records. When a zone is first
read in there is an implicit $ORIGIN zone-name. The current $ORIGIN is appended to the domain
specified in the $ORIGIN argument if it is not absolute.
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
is equivalent to
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
The $INCLUDE Directive
Syntax:
$INCLUDE filename
[origin][comment]
Read and process the file filename as if it were included into the file at this point. If origin is specified the
file is processed with $ORIGIN set to that value, otherwise the current $ORIGIN is used. The origin and
232 Hewlett-Packard Company − 25 − HP-UX 11i Version 2: December 2007 Update