How to set up a DMZ

Fortunately, a demilitarized zone (DMZ) deployment on a network is quite simple. A DMZ is a protected middle ground network where you can deploy servers that offer services to the public. Building one is a simple matter of using a firewall with three network interface cards, configured as shown in the diagram below:

Then, using the firewall, create rules that allow the minimum necessary traffic between zones, subject to the following conditions:

• Systems from the Internet may not connect directly to the intranet.
• Systems from the intranet may not connect directly to the Internet.

The second rule is sometimes omitted for simplicity of implementation. When you do choose to implement your network in this fashion, place a proxy server in the DMZ that users may access when they wish to request information from an Internet-based Web server (for example).

The use of a DMZ implementation to isolate publicly accessible systems is one of the longest-standing principles of information security. I encourage you to pursue this avenue as quickly as possible if you have not already done so. For more information on this topic, read Placing systems in a firewall topology.