Demilitarized Zone (DMZ) is your front line, which protects valuables from direct exposure to an untrusted environment. In other words, a DMZ is generally a secure network segment that is exposed to the internet, where you keep valuable resources like a web server (the most common internet application) to enhance application security by adding an extra layer of security. It's very important to carefully plan and design a DMZ because it may not be easy task to fix loopholes when handling production traffic.
So how do you design a DMZ? Most of the time, an administrator puts the energy into securing and concentrating on DMZ security only and forgets about the rest of the internal data communications designed to access valuable information. Access to the DMZ from an internal application should be locked down as tightly as possible.