To replace something, you embrace it and extend it so the old version can be effectively phrased out.
Who's arguing for that? That would be completely non-viable even today, and even with NAT64 it would be annoying.
> Dual-stack fails miserably when the newer stack is incompatible with the older one.
Does it? All my clients and servers are dual stack.
> With a stack that extends the old stack, you always have something to fallback to.
Yes, v4/v6 dual stack is indeed great!
> To replace something, you embrace it and extend it so the old version can be effectively phrased out.
Some changes unfortunately really are breaking. Sometimes you can do a flag day, sometimes you drag out the migration over years or decades, sometimes you get something in between.
We'll probably be done in a few more decades, hopefully sooner. I don't see how else it could have realistically worked, other than maybe through top-down decree, which might just have wasted more resources than the transition we ended up with.
I don't see IPv4 going away within the next fifty years. I'd not be surprised for it to last for the next hundred+ years. I expect to see more and more residential ISPs provide their customers with globally-routable IPv6 service and put their customers behind IPv4 CGNs (or whatever the reasonable "Give the customer's edge router a not-globally-routable IPv4 address, but serve its traffic with IPv6 infrastructure" mechanism to use is). That IPv4 space will get freed up to use in IPv4-only publicly-facing services in datacenters.
There's IPv4-only software out there, and I expect that it will outlive everyone who's reading this site today. That's fine. What matters is getting proper IPv6 service to every Internet-connected site on (and off) the planet.
They’re already not. For example, I believe you won’t get an iOS app approved for distribution by Apple these days if it doesn’t work on v6-only clients.
That's not what I said. I said that having a globally-routable IPv4 address assigned to a LAN's edge router will stop being a thing. Things like CGN (or some other sort of translation system) will be the norm for all residential users.
> ...but servers (or at least load balancers) will absolutely not stay v4-reachable only.
Some absolutely will. There's a lot of software and hardware out there that's chugging along doing exactly what the entity that deployed it needs it to do... but -for one of handful of reasons- will never, ever be updated ever again. This is fine. The absolute best thing any programmer can do is to create a system that one never has to touch ever again.
That's still what I would call a v6-only (with translation mechanisms) client deployment. Sorry for being imprecise on the "with translation mechanisms" part.
> Some absolutely will.
Very few, in my prediction. We're already seeing massive v6 + CG-NAT-only deployments these days, and the NAT part is starting to have worse performance characteristics: Higher latency because the NATs aren't as geographically distributed as the v6 gateway routers, shorter-lived TCP connections because IP/port tuples are adding a tighter resource constraint than connection tracking memory alone etc.
This, and top-down mandates like Apple's "all apps must work on v6 only phones", is pushing most big services to become v6 reachable.
At some point, some ISP is going to decide that v6 only (i.e. without translation mechanisms) Internet is "enough" for their users. Hackers will complain, call it "not real Internet" (and have a point, just like I don't consider NATted v4 "real Internet"!), but most profit-oriented companies will react by quickly providing rudimentary v6 connectivity via assigning a v6 address to their load balancer and setting an AAAA record.
I agree that v4 only servers will stick around for decades, just like there are still many non-Internet networks out there, but v4 only reachability will become a non-starter for anything that humans/eyeballs will want to access. And at some point, the fraction of v4-only eyeballs will become so small that it'll start becoming feasible to serve content on v6 only. At that point, v4 will be finally considered "not the real Internet" too.
Sure, I agree. I'm not sure how you got the notion that I thought a large percentage of systems out there will never get IPv6 support. There's a lot of solid systems out there that just fucking run. They're a small percentage of all of the deployed machines in the world.
> That's still what I would call a v6-only (with translation mechanisms) client deployment.
When people say "IPv6 only", they mean "Cannot connect to IPv4 systems". IMO, claiming it means anything else is watering down the definition into meaninglessness. Consider it in the context of what someone means when they envision a future where the Internet is "IPv6 only", so we don't need to deal with the "trouble" and "headache" of running both v4 and v6.
> We're already seeing massive v6 + CG-NAT-only deployments these days...
Yeah, it's my understanding that that's been the situation for a great many folks in the Asia/Pacific part of the world for a while now. Lots and lots of hosts, but not much IPv4 space allocated.