Not just NAT Type 2, but also you need the necessary ports forwarded (manually, DMZ or UPnP).
If you have NAT type 2 that means that the ports are open. Otherwise you can't have NAT 2 on the PS3
Nope. NAT Type 2 just means that you use a router to access internet. Some people have NAT Type 2, but UPnP is disabled.
NAT Type 1 means that your PS3 doesn't even need a router, since it uses an public IP.
Read this article thoroughly if you want to understand how it works: http://netnix.org/2011/09/06/understanding-ps3-nat/
Here is Sony's explanation on router port settings:
Connecting to PlayStation®Network
When using PlayStation®Network in an office or a housing complex, security features such as a firewall may block the communications. In this case, refer to the following instructions.
In PlayStation®Network, you can communicate with PlayStation®Network servers on the Internet or directly with other PS3™ systems. Communication with PlayStation®Network servers on the Internet is done mainly when:
- Signing in / signing out
- Using your Friends list or block list
- Exchanging messages
- Using (PlayStation®Store)
The port numbers for PlayStation®Network servers used for this are TCP: 80, 443, 3478, 3479, 3480, 5223, 8080 and UDP: 3478, 3479.
For voice / video chat and online game play, direct communication with other PS3™ systems is used for data transmission during voice / video chat and online gaming. The port number used for this is UDP: 3658. However, you may need to use a different port number when you are connected using a NAT router.
- When you are using a router, direct communication with other PS3™ systems may be restricted depending on the type of router and its settings. When using a UPnP-compatible router, enable the UPnP feature.
- Communication may be restricted by routers and security functions provided by Internet service providers. Refer to the instructions supplied with the network device and the information from your Internet service provider.