DynDNS native backend - deSEC - v6 overwrites v4 update and vice versa

[jaeti01]

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Affected Version
OPNsense version: 24.1.2 (the problem seems to exist for longer as forum discussions indicate)

Describe the bug
The DynDNS native backend has support for deSEC-v4 and desec-v6 with two independent services.
So in order to update both, two service entries are needed.
The deSEC API has a speciality that when you update only v6, the v4 address get's deleted and vice versa. They do this intentionally to avoid a stale address been left over.
To avoid this, there is a special parameter "preserve".
Documentation here:
https://desec.readthedocs.io/en/latest/dyndns/update-api.html

The solution is to either:

• update both addresses in a single service or
• use the preserve parameter to avoid the other one been overwritten

To Reproduce

Steps to reproduce the behavior:

• Navigate to Dynamic DNS
• Configure "Native backend"
• Create a DynDNS service for deSEC v4 for <hostname.domain.tld>
• Create a DynSNS service for deSEC v6 for <hostname.domain.tld>
• Trigger an IP change
• observe that only v4 or v6 is been set (depending on the execution order)

Expected behavior

• Both addresses (A and AAAA) for the same hostname should be properly updated

Describe alternatives you considered

• currently using service "custom"with
  https://update.dedyn.io/?hostname=<hostname>&myip=__MYIP__&myipv6=preserve https://update.dedyn.io/?hostname=<hostname>&myip=preserve&myipv6=__MYIP__
  This works as a workaround, but has no errorhandling.

Add any other context about the problem here.

Environment
OPNsense 26.1.2-amd64.

Forum Reference
https://forum.opnsense.org/index.php?topic=41468.new

[max-foss]

Updating both addresses likely won't happen unless we reintroduce the 3rd option but given how IPv6 work it is often treated differently without NAT. Appending the preserve to the other should be easy.

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