You took the wrong approach to this. My advise is that you take some time to understand how the Internet works. Only after that will you know what you need to do.

A simpler way would be to run squid or some other app, on your gateway machine and use ACLs (Access Control Lists) to block sites, based on domain, not port.

I cannot explain further since your presentation of the problem does not reveal much about how you are doing what you are doing (or trying to do).