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I had a customer today using 4G in Australia that only got IPv6 connectivity. They couldn't use the 4G dongle to access resources at their ipv4 only office.
I am not sure if it was a fault with the dongle, or the ISP, or some misconfiguration - but ultimately the clients using this 4G dongle were only able to hit IPv6 sites and everything on IPv4 was completely inaccessible.
I \*THINK\* that there should have been some NAT64 going on, but it wasn't working.
Regardless, I expect this is going to be a recurring problem as time goes on.