With FreeBSD, a NATD DMZ Firewall is within arms reach. FreeBSD is a free open source operating system for many different types of new or old computer equipment. It is highly configurable and easy to learn. FreeBSD® is an advanced operating system for x86 compatible (including Pentium® and Athlon™), amd64 compatible (including Opteron™, Athlon™64, and EM64T), UltraSPARC®, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX® developed at the University of California, Berkeley. First, burn a copy of FreeBSD on a CD-ROM. The FreeBSD CD-ROM is bootable.

http://www.freebsd.org/where.html

In computer networking, Network Address Translation (NAT, also known as Network Masquerading, Native Address Translation or IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or destination IP addresses and usually also the TCP/UDP port numbers of IP packets as they pass through. Checksums (both IP and TCP/UDP) must also be rewritten to take account of the changes. Most systems using NAT do so in order to enable multiple hosts on a private network to access the Internet using a single public IP address. A NATD DMZ Firewall is noteworthy because it filters all the dangerous traffic from the internet into something a private network can understand. A DMZ also acts as a gateway to the internet for all machines on a private network.

To get started, install two RJ-45 network cards. Then connect a CAT-5 cable from the RJ-45 port on the first Ethernet device to a HUB. Then connect a CAT-5 cable to the second Ethernet device and connect the other end of the cable to a ethernet cable modem or a DSL modem. This device is thereby isolated from the HUB. Then connect any workstations or additional servers to the hub.