networking - Portforwarding to multiple computers

Me and my brothers are playing the computer game GTA Online. We are all connected to the same local network.

However we experience connection problems sometimes. Now I read on the official Rockstar site that it will help to unlock/forward some ports in my router.

However, for a single computer this makes sense to me, but how does the router deal with incoming packages, if I defined the follwing two port forwarding rules?

You can see that I forward for example port 80 to computer Black and Black2. Will computer "Black" and computer "Black2" receive all incoming packages on port 80 of the router now, and other computers won't receive anything?

And does computer Black also receive the packages which are targetted to Black2, or only his packages?

How does the router know the correct target?

Answer

Packets received at port 80 etc. are going to be forwarded to ONLY ONE internal pc, either Black or Black2.

Will computer "Black" and computer "Black2" receive all incoming packages on port 80 of the router now, and other computers won't receive anything?

Incoming packets on port 80 of the router's external interface are going to either Black or Black2. It is hard to tell which one, it depends on the order in which the router internally processes the rules. The fact that Black comes first in your web management does not necessarily mean that its rules have a higher priority than those regarding Black2. One thing is correct, though: other computers won't receive anything.

Does computer Black also receive the packages which are targetted to Black2, or only his packages? How does the router know the correct target?

This is the crucial point: there is no way for the router to tell whether a packet is intended for Black or Black2. It cannot discern between them and is probably going to send all of them to Black or Black2. It can also happen that some of them go to Black and some go to Black2, but those won't be the "right" ones. Since you are forwarding more than one port, it can happen that packets incoming on one port are going to Black and packets incoming on another port go to Black2. There is no predicting this since you gave the router ambiguous directives.

What can you do?

You have to take control over which packets go where. I see two ways.

1. one is to enable only one set of rules and play with e.g. Black. When you want to play with Black2, go back to the router's management interface and make the switch: disable Black and enable Black2. I know that this is not what you want and you are looking for a way to play simultaneously on the two PCs.


2. another is to configure the clients to use two different sets of ports, and create two different sets of forwarding rules on the router. I mean opening the game settings and seeing if there's such an option. It is howerever possible that this cannot be done, it depends on whether the game manufacturer envisaged this possibility. This kind of setup is very common in the server world, but in the consumer market it is often expected that there is only one workstation and it is directly connected to the Internet.