In theory, how IPv4 is better than IPv6? I need only advantages of IPv4 for study purposes.
In another words - what are the pros of IPv4?
Legacy support is the only one I can think of. It's been implemented and re-implemented to the point that just about everything out there would support it properly so lowest-common-denominator cheap equipment shouldn't, in theory, screw it up.
IPv6 is compatible with IPv4 but it's not widespread enough to the masses to show bugs in implementations yet, in my opinion. I'm sure someone's Internet enabled doodad will bug out because of an issue with interacting on IPv6.
And the main point is that the switch from IPV4 to IPV6 lacks of a plan-b and right now, the migration is not working so well.