I have an Azure VM whose Azure Network and adapters are all configured for IPv4 only. Among other things the provides backend services a for a phone app. We rebooted the VM last evening. There were no changes made to Azure or app, just rebooting to reset an app cache issue. All phones that prefer IPv6 are failing to connect. It appears that Azure DNS is returning an IPv6 address to the phones when no AAAA records are stored in the zone what-so-ever. Here is a screen snap from a phone that clearly shows Azure DNS is returning an address, one we don't control. It's clear Azure DNS is returning "2607:7700:0:1a::682c:1742" and there's no entry for it in our zone.
Any ideas on how to resolve this? We are working on a plan to move to another DNS provider.
The problem is caused by T-Mobile performing an IPv6 to IPv4 proxy.
If your customer base includes mobile devices, I recommend implementing IPv6 end-to-end. This means adding DNS AAAA resource records, configuring IPv6 listeners for load balancers, and enabling IPv6 at the virtual machines.