Thanks for your answer.
Actually I tried to use the port forwarding but I did not succeed. I did the following:
imagine the real DNS server is 188.8.131.52
the external address of zeroshell is 184.108.40.206
the internal address of zeroshell is 192.168.2.1
within the DNS page of zero shell I activated the port forwarding as:
in the clients (192.168.2.2) DNS configuration I put 220.127.116.11
It did not work. I co not understand why.
Where am I wrong??