No, I followed that guide and people were able to join my party who previously couldn't. The problem is that the game became unplayable.
Now that I've reset my router (removed all port forwarding and DMZ, etc) the game runs decent again, but of course my party issue is back.
Nah, I've got no ports forwarded, just uPnP turned on. I thought maybe I'd just suffer the same lag problem if I forwarded any ports again.
If you have UPnP turned on, you should be fine. There is no need to manually forward ports or use DMZ mode.
I had this problem too. My Swisscom Router blocks everything (Netopia -_-). I am trying to find out a way with my network- uhm electician XD. He gave me now a long LAN cable to connect directly to the hub (without wireless LAN). This did only work, with opening the Port Sony mention on the network configurations and a direct IP-forwarding to my PS3. With that I get a NAT 1 connection.
Now we will try to find out how to get at least a NAT 2 connection on wireless (it did work with a direct IP-forwarding, but it disconnected me after every hour/second game).
Shadow, you seemed as if you had a solution for me. Do you think opening those ports (without doing all the other things such as DMZ) will help my situation?
I think yes.
DMZ and port forwarding donot work well together. For best results, either DMZ or port forward the needed ports, donot do them both.
So, try opening all the ports I listed, if it didn't work, port forward the ports listed in the guide too. I think that should work. Donot put your PS3 into DMZ, only port forward the ports of PSN and SCEA servers.
What router do you have by the way? Maybe you're port forwarding the wrong way?
Try to directly forward the IP (must be available in the router settings), but make sure you have chosen the right system (your PS3). You can give the PS3 a name in the network settings to find it easier in the router settings.
This might help, but it could be that it doesn't work either. Then you have kind of additional security features within your provider, which are blocking, dunno if you can switch that off.