To the best of my knowledge, Comcast is running dual-stack v4 and v6. The GP was talking about running a purely v6 network, and pointing out that it wasn't yet feasible. Your example of Comcast doesn't really fit the bill because Comcast already has a v4 network to all of their customers, and they are not migrating customers to a solely-v6 network.

This is the chicken-and-egg problem that all new networks are facing with regard to IPv6 adoption. In order to have a usable network, you have to support IPv4 to all endpoints. But once you have v4 at all endpoints, the incentive to run v6 is greatly diminished.

As always, v6 needs a "killer app" that Grandma wants to use that is unavailable over the v4 internet, and then network administrators could use the actual demand from their customers as a justification for moving to v6. Unfortunately, at the moment, the list of v4-only must-have apps is still greater than the list of v6-only must-have apps.

> The GP was talking about running a purely v6 network, and pointing out that it wasn't yet feasible.

Amusingly that's how mobile/smartphones are supposedly run: the devices get IPv6-only, and if they need to hit an IPv4-only address they are CGNATed.

* https://www.internetsociety.org/resources/deploy360/2014/cas...

* https://blogs.akamai.com/2016/06/preparing-for-ipv6-only-mob...

Ah, so that explains it. I just switched from Sprint (which always gave me an IPv4 address) to T-Mobile (which gives me an IPv6 address).

My Verizon iPhone has both a public IPv4 address and a public IPv6 address.

They certainly could be using CGNAT, but that seems like a weird way to do it.

> My Verizon iPhone has both a public IPv4 address and a public IPv6 address.

How are you able to tell with IPv4? You cannot run ifconfig on an iPhone, so how are you determining that?

There are apps like "Network Analyzer" that give you this info. (My MVNO puts me behind CGNAT, no IPv6)

Seriously? On Android it's just settings->about phone

Really? My Verizon Android gets RFC6598 space.

Holy cow, I don't know how I was never aware of RFC6598. When I saw the address starting with 100, I simply assumed it was an actual routable IP.

v6 with DS-Lite/464/MAP is going to be cheaper than v4-only because it allows the ISP to sell off (or not buy) most of their v4 addresses while also using less equipment. T-Mobile has already adopted this architecture.

Maybe you just don't get to know what problems it causes because they don't talk about it. Dual stack is currently under testing and afaik higher ups are not very happy about it.

Maybe we've done too early (it was about five years ago maybe, I don't really remember exactly) and now tooling is better, idk