Quite some time has passed since the first post and here in Germany nation-wide IPv6 roll-out is underway.
Nowadays most devices support sending DDNS updates when the public facing WAN address changes. It turns out it’s quite the opposite for IPv6, since (depending on the addressing scheme in use) usually the prefix for the whole network changes while the host-specific part may stay the same. I also wanted to keep the old IPv4 DDNS update job and port forwarding intact as a fallback.
After fumbling a bit with the configuration I found that you can have the Fritz!BOX make multiple update requests (in this case for A and AAAA) at once.
Just select DDNS Provider Benutzerdefiniert (Custom) and enter the full update URLs separated by a space into the field while replacing the angle quotes with the actual credentials:
https://ddns.provider/url?username=»your username«&password=»super secret password«&myip=<ipaddr>&hostname=1 https://ddns.provider/url?username=»your username«&password=»super secret password«&myip=<ip6addr>&hostname=1
Unfortunately the input field validation requires the username and password to be set, so when we enter bogus login credentials, both requests will contain those as POST data along with the correct ones in the GET header fields.
Your mileage may greatly vary between the different DDNS providers. Mine happens to allow updates containing valid and invalid login credentials at the same time!
While this currently works for me, there is still the need for a solution that does not have that hacky feel to it.