cannot connect to people using NAT punching

[hrmph]

This has been happening to me constantly and I finally figured out the cause of it. What has happened several times is that I'll join a game and the game starts and the map loads fine but I get the connecting to host countdown. It nevers connects and always times out. Today I realized that it only happens when the person hosting is using NAT punching. All of the other players join the game just fine. So my question is, what is wrong on my end that doesn't allow me to connect? BTW I can host fine without NAT punching (via port forwarding).

EDIT: I figured it out.. I had my router's DMZ option set to the ip address of my older computer.