In the previous post I had a closer look at the ipv6-only APN of my mobile network operator of choice and how that brings me a step closer to the future of the Internet as it should be. By configuring and activating an additional APN profile, a device can instruct the network to only assign an IPv6 address and to perform DNS64 to reach IPv4 only hosts on the Internet. It works great while I’m in my home country but a bit of care needs to be taken to configure the APN profile properly for roaming.
So What’s The Problem
When roaming, a part of the bearer establishment is controlled by the visited network. The problem with that is that you never know if the visited network is actually capable of supporting an ipv6-only bearer. There are the same worries when it comes to ipv4v6 dualstack bearers, as only a minority of network operators make dualstack bearers available to their customers. I travel a lot but I never had a problem with dualstack bearers so far. Even if not supported for their own customers, the majority does support such bearers with full ipv4v6 capabilities for roamers these days. I’ve come across a few operators that only assign an IPv4 address for a dualstack request, but o.k. one can live with that for some time as well. I haven’t yet come across one that downright failed with an ipv4v6 dualstack APN, although I have heard reports that some network operators do not handle dualstack bearer requests properly and send a wrong result code. This in turn makes the mobile request a separate ipv6 bearer which does not make a lot of sense in practice. Not the mobile’s fault, it’s a shitty roaming network operator configuration.
The Proper Roaming Config For My IPv6-only APN Profile
Anyway, back to the ipv6-only APN profile. When I was recently in Austria, I set my ipv6-only APN profile to ‘ipv6 while roaming’. What I got was 3 out of 3 network operators failing with that and a nice bouquet of different reject causes. No connectivity at all. But at least all three could handle an ipv4v6 request properly. So for roaming it’s better to set the APN profile to ipv4v6 or, if you want to be 101% sure, to ipv4. But where’s the fun in that?