Simple Firewall

Question

Hi all,
I have very recently begun using java as a development package, and I love the network capability that it has. It makes it quite a bit easier to make a network application, and implement it.
Something I would like to try would be to make a fairly simple firewall. For instance, when a user inside the network wants to make a connection, it would forward it through to the outside world, and keep the thread open to allow communication back to the host. If the outside world tried getting in, it would reject the host unless is met specific requirements (right port, etc).
Three questions I have:
1. Is this possible? I mean, it seems possible, but would there be a problem with the data, even if I used very basic I/O streams and such? Or would there be problems because of the vast number of protocols and such?
2. How can I differentiate between 2 NICs? On my existing firewall, I'd have eth0 and eth1 for my internet and local net Ethernet cards. How would java know which is which? Creating a server socket is simple, but how do I tell it which interface to listen on?
3. Obviously a firewall would need to listen to all incoming and outgoing ports. Do I seriously need to make 65535 threads to have a server socket listen on every port? I would hope there is a more simple way, but I'm just not finding it anywhere.
Thank you all for your time.

Answer 1

Yes it is possible with java.net API.
There are lot of examples.
I think you shoulg go to the socket programming division
if you realy like to this.