You're right and I used to do the same for years (dyndns xD) But my current ISP required me to pay extra for a static IP, where their ordinary "dynamic IP" off

You're right and I used to do the same for years (dyndns xD) But my current ISP required me to pay extra for a static IP, where their ordinary "dynamic IP" offering shares IP and don't allow for direct connections from the internet. This never used to be the case.