Imagine two ppl in your home wanting to setup their own web servers. You face the same dilemma ANYTIME you need to support services behind your NAT router. The machine w/ the port forward is getting its own traffic AND traffic intended for the other machine, meanwhile the other machine is completely starved! So the traffic for that port will ALWAYS be forwarded to the machine w/ the port forward. Given traffic at port X, should it be forwarded to the machine designated in the port forward, or dumped into the DMZ? ThereвЂ™s no way for the router to decide.

Put yourself in the position of the router. But once you add a second machine, unless you can use different ports, youвЂ™re stuck.ДЄnd no, you canвЂ™t use port forwarding for one machine and place the other in the DMZ. There's simply no way to disambiguate traffic received at the router's firewall on port 'X' and decide which of those two machines the traffic should be forwarded to. If you have two machines behind a NAT router that both require the same ports to be opened and forwarded, you can't do it.

Strangely enough though, we were able to play once with the router set on default settings(meaning UPnP off and firewall on), but were unable to any other time.Дoes Bad Company 2 allow the port changing? Wait, just so I'm getting this right, even if I forward my ports and/or set UPnP on, I'm not going to be able to play both at the same time? However, thereвЂ™s a downside this invariably limits the features available. ItвЂ™s usually some setting that changes the NAT type (open, moderate, strict). Other games may allow you to reconfigure the game to minimize (if not eliminate) the need to open ports. Thus you could each have your own unique port configuration and not step all over each other. NOTE: In order to accommodate multiple players behind a NAT router, some games will allow you to change the default ports. But thatвЂ™s not typically an option from your ISP (or if it is, it will result in additional fees). Of course, if you each had your own public IP and router, that would resolve the problem. ThatвЂ™s just a limitation of living behind a NAT firewall. And back and forth you go in a vicious circle, each kicking the other out of the game.

So each time one of you attempts to use the same game (and by definition the same ports) from different PCs/gaming consoles, it reconfigures the port forwarding in favor of the new player. Any given port can only be forwarded to ONE machine.

UPnP allows the game itself to open the ports it needs on the routerвЂ™s firewall and forwarded them to itself.Д«ut thereвЂ™s a catch. The other is to use UPnP (Universal Plug N Play), which if you didnвЂ™t manually open and forward ports and it works when using a single PC/game console, is probably how itвЂ™s working at the moment. The first is to use the port forwarding feature of your router (i.e., manually). There are two ways to handle port forwarding. A game will require one or more ports to be opened and forwarded to the correct machine on your local network. It works great until you have a need to allow unsolicited INBOUND network traffic (e.g., online gaming). The problem is that both of you are behind a NAT router.ДЄ NAT router maps the single public IP address provided by your ISP (e.g., 209.157.4.3) to a local IP address space (e.g., 192.168.1.x) and uses its firewall to protect your internal network from Internet threats.

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