PS3 - Can't connect to some friends

[Wu Kenny Lee]

I have got a strange problem with GTA IVs Multiplayer, and with some other special Games with Multiplayer-Modes (Red Dead Redemption, Fifa 11, Dead Space 2): I can connect and join rooms of some friends of mine, but with some of them, I've got connection issues.

That means: I can just connect to them rarely, if it doesnt work, the game just kick me out of the room/server if they try to join or if I try.

But sometimes, and I dont know why, I can connect to them without any troubles.

And this is just a problem with some friends of mine. Well, because I know the most of my PSN contacts, I asked them if they've got trouble to connect to other players. But they dont have these connection problems with other players, just with me.

But the strange thing is: I can still play other games online against the same guys who couldnt connect to me in the games I mentioned above.

 

Ive tried nearly everything: Ive got NAT Type 2, UPnP is activated, DMZ is activated, I changed the MTU of my PS3 to 1492 which is the MTU of my router, I even changed my DNS servers. I also tried to connect it with a LAN-cable to my router instead of using the WLAN functions, but it still doesnt work.

Also, the PS3 says something about "The router may does not support IP-fragments" ...

 

Does anybody know a solution for my problem?