Comment by paperplatter 10 months ago
IMO the separate-stack nature of ipv6 was a mistake. I can see why they did it, but the changes could've been a lot more incremental otherwise, and we might've been done already. Everyone talks about the biggest change being the 128-bit address space, but the real leap is that pre-existing ipv4 blocks weren't preserved in ipv6.
> It is a common misunderstanding (I hear “we could have just made IPv4 bigger” a lot) but apart from the routing issues above (needing to replace every router before it could work at all), the endpoints are also a problem.
Don't forget all the DNS software: "A" records are hard-coded to 32-bits, so if you wanted >32 you needed a record type (what we now call "AAAA", RFC 3596).
Then all the DNS programming APIs had to be updated and all the C header files with new structs.
I'm not saying we can avoid updating routers/hosts/DNS/etc, but it's only one piece of the migration puzzle. Otherwise we'd be done already. I elaborated when responding to a similar question: https://news.ycombinator.com/item?id=41603782
> Everyone talks about the biggest change being the 128-bit address space, but the real leap is that pre-existing ipv4 blocks weren't preserved in ipv6.
You mean like RFC 2765?
RFC 2765 isn't about keeping ipv4 blocks in ipv6, if I understand correctly. It's about translator boxes for ipv6-only hosts to talk to ipv4-only ones by acquiring temporary ipv4 addresses.
You can; but I'd not be surprised if there are commercial setups that use IPv6 packets for everything, including situations with IPv4 addresses. I think it would allow getting rid of most of the ethernet header overhead, by basically just talking bare IPv6 packets.
The changes couldn’t have been more incremental. Routing hardware only understood the IPv4 header (and at that time I believe a lot of this was baked in silicon). There was no way to create an IPv4+ without needing to replace all the internet’s routers before it could reliably work.
How would have it made it easier to migrate when all of the new blocks wouldn’t be accessible (in either direction) if the traffic passed through any router that hadn’t yet been upgraded? Nobody could really use any of the extended space at all until every single router had been upgraded to this IPv4+.
It is a common misunderstanding (I hear “we could have just made IPv4 bigger” a lot) but apart from the routing issues above (needing to replace every router before it could work at all), the endpoints are also a problem. Nothing in the expanded space could actually call out to a legacy IPv4 endpoint - it could sent packets to it, but that legacy host wouldn’t be able to return packets back since it wouldn’t understand the larger address. And of course the legacy endpoint couldn’t initiate a connection to anything in the extended space either from its side.
So you not only have all the same problems of IPv6 (like needing to upgrade everything), you actually add a bunch of problems of breaking the ability of big parts of the internet from being able to communicate with the rest.
Dual-stack was necessary because everything couldn’t be switched over on the same day. If everything was upgraded at once, your extended-IPv4 idea would work, but otherwise it would break the internet!