$TTL 21600
$ORIGIN 2.0.192.in-addr.arpa.
@       IN      SOA     ns0.example.com. hostmaster.example.com. (
                        2020010100  ; Serial #
                        3600        ; Refresh
                        900         ; Retry
                        2592000     ; Expire
                        3600 )      ; Minimum TTL

        IN      NS      ns0.example.com.
        IN      NS      ns1.example.com.

;$ORIGIN 2.0.192.in-addr.arpa.
2       IN      PTR     mx0.example.com.
5       IN      PTR     ns0.example.com.
8       IN      PTR     srv0.example.com.