[graf_von_anonym]

Depending on how you are viewing this webpage, there should be the word "connection" in the top half of the block near the top of this page that includes the forum path and your User CP button.

That aside, I think you have successfully diagnosed the issue - your IP address is dynamically assigned, though it can often be re-assigned to a single MAC address for periods of a year or more. That last part is key; there's no way to reassign the IP given to a specific MAC address, but changing the MAC address will often result in a new IP address being assigned - however, as with most semi-random systems there's no guarantee that changing the input will result in a different output. That said, it's your best shot.