[HOWTO] - DynDNS with deSEC using preserve (A + AAAA without overwriting)

[skywalker007]

Problem
When using OPNsense DynDNS with deSEC, updating IPv4 (A) and IPv6 (AAAA) separately can overwrite the other record.
This is confirmed behavior and documented in the deSEC API. The fix is to use the preserve parameter and the custom updater.

IPv4 DynDNS Configuration (A Record)

Create a DynDNS entry:

Service: custom
Protocol: Custom GET
Server:

Code Select Expand

https://update.dedyn.io/?hostname=<FQDN>&myip=__MYIP__&myipv6=preserveUsername: <FQDN>
Password: <DESEC_TOKEN>
Hostname(s):<FQDN>
Check IP Method: Interface IPv4
Interface: WAN

Important Notes

__MYIP__ must be included in the URL.
OPNsense only inserts the detected IP if the placeholder exists.
myipv6=preserve ensures the AAAA record is not deleted during IPv4 updates.

IPv6 should be configured as a separate DynDNS entry using:

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https://update6.dedyn.io/?hostname=<FQDN>&myipv6=__MYIP__&myipv4=preserveCheck IP Method: Interface IPv6
Interface: <one of your internal v6 assigned interfaces>