17.3.4. Reverse Name Resolution Zone Files

17.3.4. Reverse Name Resolution Zone Files

A reverse name resolution zone file is used to translate an IP address in a particular namespace into an FQDN. It looks very similar to a standard zone file, except that PTR resource records are used to link the IP addresses to a fully qualified domain name.

The following illustrates the layout of a PTR record:

<last-IP-digit> IN PTR <FQDN-of-system>

The <last-IP-digit> is the last number in an IP address which points to a particular system's FQDN.

In the following example, IP addresses through are pointed to corresponding FQDNs. It can be located in /var/named/example.com.rr.zone.

$ORIGIN 1.0.10.in-addr.arpa. $TTL 86400 @ IN SOA dns1.example.com. hostmaster.example.com. ( 2001062501 ; serial 21600 ; refresh after 6 hours 3600 ; retry after 1 hour 604800 ; expire after 1 week 86400 ) ; minimum TTL of 1 day 1 IN PTR dns1.example.com. 2 IN PTR dns2.example.com. 5 IN PTR server1.example.com. 6 IN PTR server2.example.com. 3 IN PTR ftp.example.com. 4 IN PTR ftp.example.com.

This zone file would be called into service with a zone statement in the named.conf file similar to the following:

zone "1.0.10.in-addr.arpa" IN { type master; file "example.com.rr.zone"; allow-update { none; }; };

There is very little difference between this example and a standard zone statement, except for the zone name. Note that a reverse name resolution zone requires the first three blocks of the IP address reversed followed by .in-addr.arpa. This allows the single block of IP numbers used in the reverse name resolution zone file to be associated with the zone.

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