As I understand it, you can play freely with dynamic IP addresses without any Hamachi. In the 2000-2007 period, people played freely through modems, without Hamachi or other clients, simply by finding out the opponent's IP address and connecting to it. With the advent of networks and static IPs, everything changed.
Or maybe the issue isn't with dynamic and static IPs, but with something else. I'm not an expert in the technical details.
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