You're partially right. Your apps need to support IPv6 because the internet connections can be IPv6 only. I believe T-Mobile is a big one does this. They do translation for their clients to the IPv4 internet, so they'll be hitting your IPv4 server through a translation layer. The client is still IPv6 only.

That doesn't make sense. If I hit amazon.com on my browser, which is IPv4 only, t-mobile needs to provide a (private) IPv4 IP to the phone to make that possible.

Edit: was totally wrong about this: https://www.internetsociety.org/resources/deploy360/2014/cas...

iOS (since IOS 12) and Android have native clients that can tunnel IPv4 requests over an IPv6 only network that are used for providers like T-Mobile.

Not necessarily.

T-Mobile could respond to DNS requests with an IPv6 address that includes an encoding of Amazon.com's IPv4 address in it so that when you try to connect it it, the gateway knows what IP address you're looking for and can do the NATing there.

Of course, this is just conjecture about a possible way of making it work, and it could easily get broken if you configure your phone to use a different DNS server.

Thanks, that's a good point. Apple talks about it here: https://developer.apple.com/library/archive/documentation/Ne...