You throw away IPv4 internally. Nothing internally is IPv4. All your network address sizing issues vanish, puff, gone, because in IPv6 the subnets are always 64-bits, which means whether it's four boxes or four million boxes it fits in the same subnet. No more NAT, you just use real (globally unique) IPv6 addresses for everything, so there are no confusing debug sessions where you thought 10.4.5.6 was this box but actually because of how routing is set up it's _that_ box and so you wasted six hours.
So internally everything is _wonderful_
And then to manage the fact that some fraction of the Internet is (and for the foreseeable future will be) IPv4 only, you have edge devices that translate. They translate DNS too. If you ask for www.example.com and the answer is A 10.20.30.40 the edge devices wrap that inside an IPv6 address and provides that as your AAAA answer.
_This_ way around works, because 128 is bigger than 32. Unlike the people who magically want an IPv6 that hides 128-bits in 32-bits, which is mathematically impossible, this merely hides 32-bits in 128-bits, which is trivial.
Anyway, nothing else needs to even care, just those edge devices, and as transition continues you spend less and less money on them. In reality at any modern company you probably already spend more on edge devices you've added because somebody read about them in a magazine - anti-malware, service protection, next generation firewalls, that sort of thing.
You throw away IPv4 internally. Nothing internally is IPv4. All your network address sizing issues vanish, puff, gone, because in IPv6 the subnets are always 64-bits, which means whether it's four boxes or four million boxes it fits in the same subnet. No more NAT, you just use real (globally unique) IPv6 addresses for everything, so there are no confusing debug sessions where you thought 10.4.5.6 was this box but actually because of how routing is set up it's _that_ box and so you wasted six hours.
So internally everything is _wonderful_
And then to manage the fact that some fraction of the Internet is (and for the foreseeable future will be) IPv4 only, you have edge devices that translate. They translate DNS too. If you ask for www.example.com and the answer is A 10.20.30.40 the edge devices wrap that inside an IPv6 address and provides that as your AAAA answer.
_This_ way around works, because 128 is bigger than 32. Unlike the people who magically want an IPv6 that hides 128-bits in 32-bits, which is mathematically impossible, this merely hides 32-bits in 128-bits, which is trivial.
Anyway, nothing else needs to even care, just those edge devices, and as transition continues you spend less and less money on them. In reality at any modern company you probably already spend more on edge devices you've added because somebody read about them in a magazine - anti-malware, service protection, next generation firewalls, that sort of thing.