I found a thread that helped me a lot and made me fix my internet sharing, but I rebooted my server and now I can't find anything to help me (3 hours of looking is enough)

I have a linux server and 2 w2k machines. I want to connect to the internet through my debian server. I only have one nic in it and i want minimal firewall rules.

I want to fix this really fast, but I also want to learn to do it without help at a later point so if anyone could help me set this up really fast and maybe give me a link to some good pages for learning iptables and/or the name of a good book I would be very greatfull.

Linuxquestions.org must be the best site ever.

Take a look at the documentation and tutorials on Netfiler.
http://www.netfilter.org/

This site will teach you a lot about masquerading (internet connection sharing).

If you want a real fast solution with minimal firewall rules, visit this section of the above link. There are working scripts for iptables, ipchains and even ipfwadm. You can pretty much copy them but you need to adjust certain variables as for example $EXTIF, $INTIF, $IPTABLES and so on.

Just read through it once as you copy it and adjust the necessary variables. There are also instructions on how to start your script every time your system boots up.

Good luck!