This article represents a small guide to understanding the DMZ (Demilitarized Zone) concept and the ways to implement it on a server. It also includes useful tips on how to increase the security of such setups, with a special focus on the Linux/*NIX-type systems:

Common setups used for small and medium networks include a firewall that processes all the requests from the internal network (LAN) to the Internet and from the Internet to the LAN. This firewall is the only protection the internal network has in these setups and it handles any NAT (Network Address Translation), forwarding and filtering requests as necessary. In most cases, the firewall also runs public services accessible from the Internet, such as web services and e-mail services. Within such setups, the DMZ is thus installed on and limited, we may say, to the server.