All in all, I had so many troubles with setting up anything behind IPv6 or DS-lite, that I asked my ISP to give me an additional IPv4 address, so that I don't have troubles. While they usually provide bad service, this came for free -- but other ISPs, for example my parents' ISP, want you to pay 50 or more euros per month for an "enterprise contract" to get a dedicated IPv4. I still haven't found a way for my dad to setup his old webcam server at home such that others can reach it from the outside world, and I tried every couple months over the last 6 years or so.