FaceTime, WhatsApp UDP streams AWOL on iOS 9 beta with T-Mo US

Well...

I'm usually with you Coder on a lot of your comments, but this one not so much. I have a daughter at college many, many miles away, and frankly, Facetime helps bridge that gap - a lot. So in this case, one man's trivia is another's comfort.

How are these apps not "real" VoIP?

Using TCP/IP is fine over a private network where can depend on end to end QoS, but problematic over the internet where packet loss makes UDP more suitable. You can judge this as "trivia" if you want, but if it wasn't for the unwashed masses finding uses for smartphones you deem beneath you, they'd cost YOU more due to lack of production scale.

T-Mobile users may have noticed issues with other apps that use UDP, but these VoIP apps would get the heaviest use and is where the problem would be primarily noticed. Obviously something about the handling of UDP changes in iOS 9.3, and T-Mobile apparently handles UDP differently than other carriers as well - so whether the fix needs to be applied to Apple's side or T-Mobile's side it is good this was found during beta and not with the official release where it would be a problem for millions of T-Mobile iPhone users.

Re: Another story?

464XLAT support in iOS is the beta bit, not IPv6.

Re: Why NAT64?

Most people don't want their phone to have a globally-unique and addressable address.

It's the selling point for IPv6 that, actually, few want.

Yes, a properly configured firewall can 1:1 map the public IPs for you.

But if you have IPv4 NAT, and IPv4 clients, the easiest way to upgrade your network is to just change your external IPv4 address for a single IPv6 address.

Re: Why NAT64?

It's an IPv6 to IPv4 gateway. It's used to connect devices using IPv6 to IPv4-only servers only it doesn't work with FaceTime and WhatsApp, maybe because UDP isn't getting through.

Re: Why NAT64?

Can someone explain why NAT is even required with IPv6?

Technically NAT itself is not required with IPv6, however, I am running a IPv6 to IPv6 NAT (NAT66) without issues. Of course, I do not use facetime or whatapp, so I am not entirely sure how they work, but I can explain possibilities from a network standpoint. You can do anything you want if you throw enough computing power at the problem.

The issue is that ISPs need a way to enable their IPv6-only clients to get to the IPv4 internet. NAT64, is required with IPv6 for sites that do not use IPv6. They accomplish this by a complete header swap on each packet. NAT64 works with both TCP and UDP, but somehow in this case, something is not working. I am not sure if there is a tie on the client source port, or how that would work, but the NAT64 will pick a new source port at the point of NAT, with the intent of being able to map the packes back to the source. With IPv6 being larger, there is no need to swap the source ports, but on the IPv4 side, usually only one IPv4 address is tied to the NAT box. This single IPv4 address needs differentiators which usually means the NAT pick a unique port.