En port til flere IP adresser

This is application dependant in a sense. You can change the external port allocation to resolve the the correct internal port on each machine.

Say for example were using rdp which uses (protocol/port) tcp/3389, the application (RDP client) actually allows you to change the external port to connect to if you specify it after the ip. So for instance say we want to have rdp access to all 3 machines from the outside world. We can setup port forwarding to each computer

(Computer)      (internal IPort)            (external IP/port)

 Comp A           192.168.0.5:3389            203.x.y.z:3389

Comp B           192.168.0.10:3389           203.x.y.z:3390

Comp C           192.168.0.15:3389           203.x.y.z:3391

This is the purpose of a router, to create routing tables.

You'll obviously have to remember which ports are allocated to which device.

This is certainly application dependant. Find out if your application or service supports the port change, ftp clients, rdp, tftp, ssh all do.. Most 'Good' services do, as those who have constructed it have considered a NAT environment.

NAT = Network Address Translation

Most things if not at the application layer, even services in windows are tweakable via the registry. I wouldnt suggest you do this if you dont have the relavent experience. You'll potentially render your workstation inoperable if you get it wrong.

Men fårstår ikke hvordan og hvor jeg skal gøre dette?