Resource Records for Reverse-Name Resolution

Forward resolution returns an IP address for a specified domain name. Reverse-name resolution returns a domain name for a specified IP address. DNS implements reverse-name resolution by using the special in-addr.arpa and ip6.arpa domains for IPv4 and IPv6.

The characteristics for a zone's in-addr.arpa or ip6.arpa domains are usually defined in /etc/named.conf, for example:

zone "2.168.192.in-addr.arpa" IN {
    type master;
    file "reverse-192.168.2";
    allow-update { key “rndc-key”; };
    notify yes;
};

The zone's name consists of in-addr.arpa, preceded by the network portion of the IP address for the domain, with its dotted quads written in reverse order.

If the network doesn't have a prefix length that's a multiple of 8, see RFC 2317 for the format that you need to use instead.

The PTR records in in-addr.arpa or ip6.arpa domains define host names that correspond to the host part of the IP address. The following example is take from the /var/named/reverse-192.168.2 zone file:

$TTL 86400        ;
@ IN SOA dns.us.example.com. root.us.example.com. (
            57 ;
            28800 ;
            7200 ;
            2419200 ;
            86400 ;
            )
              IN  NS      dns.us.example.com.

1             IN  PTR     dns.us.example.com.
1             IN  PTR     us.example.com.
2             IN  PTR     svr01.us.example.com.
101           IN  PTR     host01.us.example.com.
102           IN  PTR     host02.us.example.com.
103           IN  PTR     host03.us.example.com.
...

For more information, see the BIND 9 Administrator Reference Manual.