Tom459

Tom459

If possible, update DynDNS directly on the access router (in your case on the Internet box) is the simpler and better solution, because the provider router is the first device to realise if the public IPv4 address actually changes.

See here. Briefly summarised: Although it is a beta version, it has proven to be so stable that it is now generally available.

@Tom459

To answer your original question:

At the time of mobile failover, i.e. when an Internet box is running on the mobile network via an LTE stick, access via DynDNS does not work and as a consequence you cannot establish a VPN connection to it from outside.