Netsys is a simple network management system utility for make esier the control of your network. You can control too much things like firewall, NAT, Servers, Pings, and more.
jennifer is an educational (albiet oddly named) firewall/NAT script generator, written in python, targetted at linux+iptables systems. It is intended to both (a) generate practical and useful configurations, and (b) demonstrate the concepts involved in TO
The use of NAT devices all over the Internet has made peer-to-peer exchanges unreliable. The rise of IPv6 should repair this, but it will still not be reliable until all peers have implemented IPv6. Such IPv6 implementation could be arranged on the fly with a tunnel mechanism that does not rely on router co-operation or manual configuration.