Game disconnected: client closed down connection. DURING GAME.

Ok, guys.

This is how I solved my problem:

All previous tests I did (as you can see all thread-long), I was behind multiple Network Equipment (Router, Load Balance, Modems and Modem/Router).

That means I was on Multiple NAT environment, and you'll see why that is important later.

I'm going to repeat: all the other games that I have/played, INCLUDING Battlefield 3, work / worked fine.

I've never needed to configure UPnP, DMZ, or Port Forwarding for them to work.

As I stated before in this topic, I have 2 Internet Connections with 2 different ISP.

One of them provided me a modem/router with locked configuration/firmware. I've tested BF4 directly connected to this ISP's router/modem, and that was it! No more "Client Closed Connection" problems.

So if you ask me what is the problem:

The BF4 makes a initial connection to EA servers to authenticate the client, before you can connect to the actual BF4 Multiplayer Server.

If you're on a Multiple NAT Network, this first connection FAILS...

...unless you're trying to connect to

1) an UNRANKED server or

2) a RANKED server with a number of players that is less than the "Minimum Players to Start" (e.g. less than 4 players, on default server configuration)

I understand that this problem might be affecting very few players that are in Multi-NAT, and that authentication to EA is important to keep cheaters outside of servers, but this is an issue that need to be addressed by EA / DICE, and not players. BF3 did not need this. Implement Multi-NAT support.