[NTLUG:Discuss] Debian Firewall

[Tim Willis]

I have an old Debian box here in my server room that I'm using IP
Masquerade in order to provide internet connectivity for the office.
I've been tasked by our corporate behemoth to put a firewall on this box
since our immanent connectivity to their core would create a back door
into their network via ours.

What firewall software is available for Debian 2.2 that is easily
configured at command line by a relative newbie like myself?

Thanks for all your help in advance!
Tim Willis