I was wondering how to make your own firewall in C++. I have a number of good books wich teaches about computer security. They explain the theory behind TCP/IP and UDP, encryption, VPN etc. , but they explain from an administrators point of view, not from the programmers. I want to make my OWN firewall, just as i usually like writing my own software instead of using an API. Makeing your own stuff requires time and patience, but its worth in the end. Now where should i begin? I know in general how a TCP-package looks like, but how do i generate them? I can write a function that creates a TCP-package, but what do i do with it then? Should i save it as a file or send it to the OS? And how do i send it to the OS? Is there and API for that? And more importantly, how do i let my program check incomeing packages and connections? Do i have to communicate with my modem or network-card direclty? (and i have NO idea on how to do that! :) ) I know a good amount of C++, but im not a master programmer (its a hobby, not a job for me). Any help would be greatly appriciated!!

I would suggest using Linux or BSD (probably OpenBSD, otherwise Free). Everything is open-source, so you can examine the current firewall code. This story should give you a little hope and direction.

Thanks Jake, that interview was interesting but: A: I dont have and cant get OpenBSD B: Its very hard to learn how a program works by looking at the source if you dont know the theory behind that type of program (a firewall in this case). Thanks for your help, but isnt there a tutoriol i can read somewhere?