This recipe refers to the regfish DynDNS product and shows the setup directly in an AVM FRITZ!Box. It is the right flow when the box itself should report IP changes to regfish.

Prerequisites

• a domain at Regfish
• enabled regfish DynDNS for the target domain
• the matching DynDNS token
• access to the FRITZ!Box web interface
• a decision whether you want to update IPv4, IPv6, or both address families

Step 1: Enable DynDNS in the Regfish domain management UI

In the Regfish management UI, enable Dynamic DNS for the target domain in the nameserver settings and note the generated DynDNS token.

That exact token will later be used in the FRITZ!Box as the username.

Step 2: Enable DynDNS in the FRITZ!Box

Log in to the FRITZ!Box web interface and open:

Internet -> Freigaben -> DynDNS

Enable DynDNS benutzen.

Step 3: Enter the matching update URL

Put exactly one of the following variants into the Update-URL field:

IPv4:

https://dyndns.regfish.de/?fqdn=<domain>.&ipv4=<ipaddr>&forcehost=1&token=<username>

IPv6:

https://dyndns.regfish.de/?fqdn=<domain>.&ipv6=<ip6addr>&forcehost=1&token=<username>

IPv4 and IPv6:

https://dyndns.regfish.de/?fqdn=<domain>.&ipv4=<ipaddr>&ipv6=<ip6addr>&forcehost=1&token=<username>

Copy the URL exactly in that shape. The placeholders <ipaddr> and <ip6addr> are substituted by the FRITZ!Box itself.

Step 4: Fill domain name, username, and password

Populate the remaining fields like this:

• Domainname: the hostname that should be updated, for example home.example.com
• no trailing dot in the domain name field
• Benutzername: your DynDNS token
• Kennwort: any non-empty value

In this FRITZ!Box flow, regfish DynDNS does not evaluate the password itself, but the field may not be left empty in the FRITZ!Box UI.

Step 5: Save and verify the first update run

Save the configuration with Übernehmen. After a few minutes, the FRITZ!Box should have executed its first DynDNS update.

Then verify success in the Regfish management UI. After the first successful update, the entry should be visible there with a comment and timestamp.

Practical notes for production setups

• use the update URL exactly as documented and do not simplify it manually
• only enable the address families that make sense for your actual line setup
• do not add a trailing dot in the Domainname field
• treat the DynDNS token as a credential and do not share it unnecessarily
• if you want to maintain both IPv4 and IPv6, the combined URL is usually the cleanest FRITZ!Box setup

Result

With this setup, the FRITZ!Box itself handles DynDNS updates for regfish DynDNS. That keeps the hostname automatically reachable through the configured access line when IP addresses change.