@devvv4ever As mentioned, I have a Dualstack Lite connection. That means that I cannot do a port forwarding for the IPv4 side of the connection as one public IPv4 is shared with several DSL lines. Only the IPv6 is a dedicated address. And there is no port forwarding on IPv6.
So, to address my NAS, I need to address it via IPv6.
I could follow your advice and do IPv6 DynDNS. But this only works with internet clients with an IPv6 address. Unfortunately, there are still DSL providers 2021 in Germany who still provide only an IPv4 address.
So, I need a protocol switcher for IPv4 sources to my NAS IPv6 destination. The easiest way is Synology Quickconnect.
I can resolve the A and AAAA record (via “dig”) of my quickconnect URL <quickconnectID>.de3.quickconnect.to to IP addresses. But how can I ensure that Davx5 deals with this correctly and also selects the IPv6 address instead of the IPv4 address?