spDYN must use "checkip4.spdyn.de" in its script

Bug and solution

Running in a dual-stack environement (IPv4 and IPv6) lead to failures in the script /usr/local/etc/spdnsupdater/spdnsUpdater.sh. This is because http://checkip.spdyn.de than returns the IPv6 address. Instead http://checkip4.spdyn.de must be called to get the IPv4 address in any case.

You need to detect a change of the IPv4 address to initiate the dynDNS update, which also works for private address ranges according to the docs of spdyn.de. Maybe (not yet tested) some additional handling for the IPv6 address has to be added to the script, but my IPv6 address changes not that often.

Important

A possible sign of a dynDNS problem is the loss of connection to the HPB service, which stops working in the default configuration when the IPv4 address changes and is not updated. For this services it should be considered to use localhost instead of the Nextcloud DNS name...

Open /usr/local/etc/spdnsupdater/spdnsUpdater.sh and trace how it obtains the address and decides whether to update. Verify the script uses checkip4.spdyn.de and detects IPv4 changes, including private address ranges described by spdyn.de. The issue also raises possible IPv6 handling, which should be clarified before considering the work complete.