Quoting doubledigit, reply 5
It doesn't connect to portforward.com, it tells portforward.com to connect to your machine on the given port, where the above program listens.
well a connection is made with the program through a stated port, to or from lets not quibble
Let me explain to you how this works.
Let's say you live in a building where people from outside are not allowed to go in, unless someone from inside allows them. Everybody from inside can exit without a problem. Someone comes to visit a person from that building and only knows the apartment number (something between 6100-6200, in this case). He will not be able to walk inside the building because, the door man does not allow him to. So, in advance, the person FROM that building tells the doorman that if someone comes to visit an apartment between 6100-6200, he should allow him and tell him where it is. END OF STORY.
This (amongst other things) is what a router/firewall does, it blocks incomming connections, so it needs to know if and what kind of incomming to allow and where to forward it to.
So, in the end, that is what the program from portforward does, it sends a signal to an outside person to come in and visit, if that person reaches the desired apartment (port number) that means that you have properly explained to the doorman who to let in.
So yeah, there's a big difference between going out and coming in a building.
To further explain why is this necesarry, well, because many people live inside buildings (read are behind routers) and to visit eachother, doormans from all the building must know what to do or some people will not be able to connect to others.
In a client/server model, everybody meets at the mall (or a public place).
Does this make any sense?