You didn't give me much to work with. For instance, if I had a "NAT capable ROUTER" based on Linux that served as your gateway to the internet, all this would be too easy. The FIREWALL would be programmed to do as you please.

Let me be blunt, I will not supply any step-by-step procedures, but will point to documentation and such may have step by step procedures. And even that may not be enough since some basic understanding of TCPIP networking will make questions such as "Why am I doing this?" at each step not be a hindrance.

Simple methods:

1. Program the firewall to do this.
2. Don't use the DNS of your ISP. Setup your own DNS and maintain it yourself with just the entries that are authorized. Figure about an hour each week to month to keep it working.

Bob