I used this method as I had a strict nat even though it's open on every other single game.
Believe me, you are not alone. It seems that IW and Activision created this game to drive us crazy. I have an open NAT on other games and when I go to play Ghosts, it tells me there's a new update for the game and when I apply the update, lo and behold, back to moderate NAT and the same lag and freeze frames as before. They really screwed us with this game.
I would like to thank you for this simple remedy to NAT type on ghost. After a week of trying to sort it out your MW2 remedy worked instantly. Thank you Happy New Year