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It's actually qemu that calls these port redirects, but I don't know the proper generic name. So what I was needed is that a service runs inside virtualbox and I want to have it on the host machine as well. For now I just wanted the same port, but for ssh obviously I want an other one, since ssh is probably already running on the host machine. ;-)
A good howto is available here. And here is an other one, in case later one of them would be 404. :-P