If you use devices in LAN to conduct a DDNS update, you can create a portmapping directly for this host without using aditional services (e.g., MyFritz).
Therefor just click on IPv6-Features in the host details of the DDNS host. There you can create a portmapper directly on this DDNS name.
Please, attend the DDNS update has be conducted from the target device.
An update via router does not work.
(Otherwise the router signals us an external IPv6 address, which does not agree with the internal network's one.)
Our FIP-Box was an application example. It cares when needed about the DDNS update autonomously and therefore an access to the router is not necessary.
In our FIP-Book we have an instruction step by step.
Download FIP-Book (7MB)