Hosting Problems on PS3?

Alright I have tried everything to be able to host a lobby on my PS3. I ALWAYS have to join their lobby and they can't join mine. I changed my DMZ opened up everything on internet connection. I just dont understand why i can't host a party with one of my friends. I have been struggling all night to play with my friend and we can't because her internet is messing up and I can't host. I am wired connection 20 plus megabits of internet speed I have had no firewall up and i still can't. I have a Belkin router with a Motorola modem. Someone help me.