How do you enable your PS3 as a DMZ host. Thanks in advance.

I have a NAT 2 connection. And how do you open a DMZ with your PS3 IP? Isnt that also harmful to your computer?

When I try to host a game on Metal Gear Online it says cannot create game with current network enviroment. I really want to be able to host games so would somebody be able to help me out. Thanks in advance.