When you start network mode in any PES version it will first try to connect to the STUN server.
Let me explain some more things about this STUN mystery and why it is needed.
Because of routers/firewalls/NAT(Network Address Translation) it is sometimes difficult to know exactly your public IP address and open ports.
This STUN protocol allows PES to discover the presence and specific type of NAT, and obtain the mapped (public) IP address (NAT address) and port number that the NAT has allocated for the PES User Datagram Protocol (UDP) connections to remote hosts.
Think of it like a www.whatismyip.com for PES and also get to know which UDP port PES uses (5730-5739).
When PES users are playing with each other all data goes through that specific open UDP port.
Normally PES would connect to the STUN server of Konami.
PES2009 had the following STUN server: pes7stun-e.winning-eleven.net
PES5 and PES6 had the following STUN server: we9stun.winning-eleven.net
So in case they're going down or you don't want to connect to their STUN server, there are luckily other STUN servers we can use.
Normally we9stun.winning-eleven.net resolves to the ip address of the konami stun server (126.96.36.199)
If you know ip addresses of other STUN servers, you can let it resolve to that other IP address.
This is done through the HOSTS file, which can be found in %SystemRoot%\system32\drivers\etc\
This file maps hostnames to IP addresses.
Own STUN server
You can also host your own STUN server and let PES connect to your local one.
For any case, the STUN server needs to know 2 different ip addresses, but most people only have one.
So just supply the following ip addresses to the STUN server,
[local network card ip address] and [localhost]
In my case this would be:
stun-server-0-96.exe -v -h 192.168.1.20 -a 127.0.0.1
PES will connect to my own STUN server, and after thats done, I can close the STUN server, because no one else can connect to my localhost.
Remember that the STUN server is only used in the beginning of network mode, only once.
Test STUN servers
You can test if a STUN server is working using the WinStun client.
STUN servers list
This is a list of working STUN servers as of 04-03-2009:
konami's stunserver -> 188.8.131.52
1- Pick a STUN server (your own, konami, from the list)
2- Modify the HOSTS file and add the ip address of the STUN server
[ip address] we9stun.winning-eleven.net
3- Save and close. Stun server solved
Known error message related to STUN problems:
"Unable to connect to server for network connection test.
The server may be too busy, down for maintenance or a firewall or router may be restricting access."
You don't have to be a rocket scientist to understand all this, if you just want to play
So a short summary for people with a short attention span.
1- PES6 needs to know the ip address of a STUN server.
2- if PES6 already works in network mode, go to step 6
3- go to C:\WINDOWS\system32\drivers\etc\ and open the HOSTS file in notepad.
4a- add the following line if you want to try a different STUN server
4b- add the following line if you want the official konami STUN server
5- save the HOSTS file
6- you're done and can go relax now.