I wanted switching to v6 to involve the minimum necessary changes. You keep your old /32. If you're sending from a /32 to a /32, it follows the same path of routers that an ipv4 packet would follow, that's what I meant by same route. There could be a v4-only router in the middle requiring translation, but I'm not even assuming that's a common issue at this point.
"or a superset in the later stages (shared down to /32, v6-only in deeper subnets)": The ipv6 state would be a superset of the ipv4 state. So if a router owns 1.2.3.4 in v4, it also owns that in v6. The ownership of 1.2.3.4.5 below that would only be part of v6 state.
What we got instead was two separate states, or parallel networks. Switching to v6 means changing everything all at once.
> Why can't the service just set up NAT64 to accept your v6 connections on their v4 servers?
It's not that simple, otherwise they would've done it. They have stuff like multiple addresses, geo DNS, and rate-limiting. Separate issue, AWS was v4-only for a long time and still treats it as more first-class because of how many internal things need to change for v6, well beyond just having hardware + OSes support it.
"or a superset in the later stages (shared down to /32, v6-only in deeper subnets)": The ipv6 state would be a superset of the ipv4 state. So if a router owns 1.2.3.4 in v4, it also owns that in v6. The ownership of 1.2.3.4.5 below that would only be part of v6 state.
What we got instead was two separate states, or parallel networks. Switching to v6 means changing everything all at once.
> Why can't the service just set up NAT64 to accept your v6 connections on their v4 servers?
It's not that simple, otherwise they would've done it. They have stuff like multiple addresses, geo DNS, and rate-limiting. Separate issue, AWS was v4-only for a long time and still treats it as more first-class because of how many internal things need to change for v6, well beyond just having hardware + OSes support it.