in-addr.arpa zone example

named.conf specifies an in-addr.arpa zone in much the same way as any other zone:

zone "203.223.128.in-addr.arpa" {
        type master;
        file "/etc/bind/db.ilab-in-addr";
        allow-transfer {
                128.223.4.9;
                128.223.6.9;
        };
};

The corresponding zone file would look like:

$TTL    86400
@       IN      SOA     203.223.128.in-addr.arpa. hostmaster.ilab.cs.uoregon.edu
. (
                     2005070800         ; Serial
                          28800         ; Refresh
                           7200         ; Retry
                         604800         ; Expire
                          86400 )       ; Negative Cache TTL
;
@       IN      NS      ilab2.ilab.cs.uoregon.edu.
        IN      NS      dns.cs.uoregon.edu.
        IN      NS      phloem.uoregon.edu.

1       IN      PTR     ilab-gw.ilab.cs.uoregon.edu.
2       IN      PTR     ilab2.ilab.cs.uoregon.edu.

In general this is similar to any other zone. Note that the PTR records are fully qualified and end with . -- this is necessary because by default a name provided for record data without the final . is presumed to be a subdomain of the origin and has the origin appended by default. If someone makes this mistake then a reverse lookup might return a result like ilab2.ilab.cs.uoregon.edu.203.223.128.in-addr.arpa.