Not your core point, but it is fun to remember that NAT wasn't always a thing, and many networks just PCs with public internet addresses and no firewalls. Even

Not your core point, but it is fun to remember that NAT wasn't always a thing, and many networks just PCs with public internet addresses and no firewalls. Even NetBIOS worked over the plain Internet back then. You could just \\x.x.x.x\c$ and it would work a decent percentage of the time.