[m01]

The way the Zyxel box is configured in modem mode on A&A results in it not having a globally routable IP address, since your router gets it instead. I expect this is a common way to setup modem mode, and it feels like the "correct default" way to do it.

This makes basic connectivity between the Zyxel box acting as a modem and the TR069 server challenging, though perhaps not impossible (you could, say, allocate a small IPv6 prefix to the modem, but I'm not sure if A&A's TR069 servers work over an IPv6 only connection).