Comment by paperplatter
Comment by paperplatter 14 hours 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.
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!