$ORIGIN 0.168.192.IN-ADDR.ARPA.
$TTL    3600
@   IN  SOA   NS1.NAMESERVER.NET.       HOSTMASTER.MYDOMAIN.COM.     (
               1402203462     ;serial
               3600     ;refresh
               600     ;retry
               604800     ;expire
               86400     ;minimum ttl
)

@    NS    NS1.NAMESERVER.NET.
@    NS    NS2.NAMESERVER.NET.

1    PTR    HOST1.MYDOMAIN.COM.
2    PTR    HOST2.MYDOMAIN.COM.