[imurray]

I think that's meant to be covered by the "IPv4x when we can. NAT when we must" part, in particular "ISPs used carrier‑grade NAT as a compatibility shim rather than a lifeline: if you needed to reach an IPv4‑only service, CGNAT stepped in while IPv4x traffic flowed natively and without ceremony."

It seemed strange that the need for CGNAT wasn't mentioned until after the MIT story. The "Nothing broke" claim in that story seems unlikely; I was on a public IP at University at the end of the 90s and if I'd suddenly been put behind NAT, some things I did would have broken until the workarounds were worked out.

[lxgr]

> "ISPs used carrier‑grade NAT as a compatibility shim rather than a lifeline: if you needed to reach an IPv4‑only service, CGNAT stepped in while IPv4x traffic flowed natively and without ceremony."

What's the difference between that and dual stack v4/v6, though? Other than not needing v6 address range assignments, of course.

[tocitadel]

Try an IPv6-only VPS and see how quickly something breaks for you. Dual-stack fails miserably when the newer stack is incompatible with the older one. With a stack that extends the old stack, you always have something to fallback to.

To replace something, you embrace it and extend it so the old version can be effectively phrased out.

[lxgr]

> Try an IPv6-only VPS and see how quickly something breaks for you.

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.

[simoncion]

> We'll probably be done in a few more decades...

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.

[lxgr]

With you on “IPv6 only will become a thing for many clients”, but servers (or at least load balancers) will absolutely not stay v4-reachable only.

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.

[simoncion]

> With you on “IPv6 only will become a thing for many 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.