In /etc/named.conf 

zone "assertis.net" {
        type master;
        file "assertis.net.hosts";
        };

In /var/named/assertis.net.hosts

$ttl 38400
assertis.net.   IN      SOA     ns.mindyourownwebsite.com. nick.assertis.co.uk. (
                        20056112502
                        10800
                        3600
                        604800
                        38400 )
assertis.net.           IN      NS      ns.mindyourownwebsite.com.
                        IN      NS      ns2.mindyourownwebsite.com.

; mail server for user@domain
assertis.net.         IN      MX      10      mail.assertis.net.
; set domain = www.domain
www                     IN      A       212.100.247.167
; Addresses of hosts
                        IN      A       212.100.247.167
ftp                     IN      CNAME   www
sites                   IN      A       81.2.119.162
167.247.100.212.in-addr.arpa.   IN      PTR     assertis.net.