I have tried setting up DuckDNS with my router and unfortunately the substitution variables provided by the router don't work quite well.

DuckDNS provides compatibility with DynDNS-like interfaces for updating a DDNS domain, but due to the current character limit on the password it requires a bit of a workaround.

According to their help page, you can use either one of these DynDNS compatible addresses for updating your DDNS (please note [duckdns domain] is just a placeholder for the actual domain):

- https://nouser:a7c4d0ad-114e-40ef-ba1d-d217904a50f2@[duckdns domain]/nic/update?hostname=exampledomain&myip=1.1.1.1&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG

- http://nouser:a7c4d0ad-114e-40ef-ba1d-d217904a50f2@[duckdns domain]/v3/update?hostname=exampledomain&myip=1.1.1.1

As you can see, username should be "nouser" and the password is 32-character access token. Trying to use this access token as the password in the router interface results in the password being cutout due to the maximum character limit on that field, thus resulting in an invalid request for DuckDNS.

The workaround I had to use was to hardcode the access token in the update URL and include the required variables in query parameters that aren't actually used by DuckDNS:

http://[USERNAME]:a7c4d0ad-114e-40ef-ba1d-d217904a50f2@[duckdns domain]/v3/update?hostname=[DOMAIN]&myip=1.1.1.1&test=[PASSWORD]

I also had to set the credentials on the router to nouser:nouser just so I could get this to work.

It would be nice if the character limit on the password field in the DDNS page would be increased to at least 64 characters.