completely baffled about hosting direct network game

[Jarkko]

There was the man who wanted to send a letter to his fiancee in another town and another country. So, he sent the letter with the address FRANCE.PARIS.AVENUEVICTORIA.24

When the letter arrived to the hotel the portier checked where the fiance lives. Ah, in room 1024, and she has deliberately told she will accept letters to be delivered. So the portier told the errand boy to run the letter to the room.

Now, replace the address with the numbers in your IP addres, portier with router and hotel room with port number, and I think you should get the basic idea. If the address number is not correct, the letter gets lost. If the portier hasn't spesifically been told to forward the letter to the room, he will throw it into the bin. If the portier does not know the correct room number, the letter gets delivered to a wrong hotel room.