This is a DNS setup for onlinetest.net server.  Assuming, the server IP=172.16.0.1.
The server can be reached at server.onlinetest.net, www.onlinetest.net, or onlinetest.net.
The server is also the mail server for this onlinetest.net domain.
Also assume that subnetmask for this network is 255.255.0.0


1: Install bind 9:

sudo apt-get install bind9

2: Edit /etc/bind/named.conf.local

# This is the zone definition. replace onlinetest.net with your domain name
zone "onlinetest.net" {
        type master;
        file "/etc/bind/zones/onlinetest.net.db";
};

# This is the zone definition for reverse DNS. 
# replace 0.16.172 with your network address in reverse notation
# - e.g my network address is 172.16.0
zone "0.16.172.in-addr.arpa" {
     type master;
     file "/etc/bind/zones/rev.16.172.in-addr.arpa";
};

3: Edit /etc/bind/named.conf.options

#forwarders {
#      # Replace the address below with the address of your provider's DNS server
#      123.123.123.123;
#};

4: sudo mkdir /etc/bind/zones

5: Edit  /etc/bind/zones/onlinetest.net.db
    (Comment must use ;)

$TTL 86400
onlinetest.net.      IN      SOA     server.onlinetest.net. root.onlinetest.net. (
; Do not modify the following lines!
                                                        2006081401;
                                                        28800;
                                                        3600;
                                                        604800;
                                                        38400
 )
;
; Replace the following line as necessary:
; ns1 = DNS Server name
; mta = mail server name
; example.com = domain name
; Replace the IP address with the right IP addresses.
onlinetest.net.      IN      NS              server.onlinetest.net.
onlinetest.net.      IN      MX     10       mail.onlinetest.net.
server               IN      A       172.16.0.1
www                  IN      CNAME   server
mail                 IN      CNAME   server
onlinetest.net.      IN      A       172.16.0.1    ; onlinetest.net IP = 172.16.0.1

6. Edit /etc/bind/zones/rev.16.172.in-addr.arpa
    (Comment must use ;)

$TTL 86400
@ IN SOA server.onlinetest.net. root.onlinetest.net. (
                        2006081401;
                        28800; 
                        604800;
                        604800;
                        86400 )
;
@                      IN    NS     server.onlinetest.net.
1.0                    IN    PTR    onlinetest.net.   ; onlinetest.net IP = 172.16.0.1
1.0                    IN    PTR    server
2.0                    IN    PTR    mail

7. Edit /etc/resolv.conf

search onlinetest.net
nameserver 127.0.0.1

Restart bind:

sudo /etc/init.d/bind9 restart

Testing:

dig onlinetest.net

References: