Dunstwolkes ISP as well as mine (KabelBW/UnityMedia) use DS-Lite (DualStack Lite) on their Fritzboxes, which means that the FritzBox is only reachable for incoming querries via IPv6 and will give IPv4 info via DS-Lite tunnel to your PC (explanation just to keep it simple, I know its tech. not really correct).
For "normal" surfing and browsing, etc. no big deal for now, but if you got a server behind the FB or use DynDNS it is an issue as well.
And for the PR server issue here it could be that due to (open) NAT querries, IPv6 is the problem and therefore we have this issue.
What I will do:
On the Fritzbox just check under the Configuration page for your internet if the connection is sth. like "IPv6/DSLite". If so, I'll call my ISP and ask to have the DS LITE option turned off in order to get "usual" DualStack, which means I will then have an IPv6 AND IPv4 public address.
If anyone has similar issue or even the same and tried this as well, it would be really appreciated if you'd share your experience
