Reverse mapping file
@               IN      SOA     ns1.sample.com. (
                               200101111       ;serial
                                14400               ;refresh after 4 hours
                                3600                 ;retry after 1 hour
                                604800             ;expire after 1 week
                               86400   )           ;minimum TTL of 1 day
;
71            IN     PTR       www.sample.com.