Hello,
I have a Nextcloud server installed at home that works well on my LAN network, but when I try to make the server accessible via a DynDNS service, I cannot connect to it. The request doesn't even reach my server. My question is whether the router immediately blocks the request, because when I set the router to be accessible (it has separately that option), I can connect without any issues over dyndns url. Could my ISP (O2) be blocking it? I can confirm that it's not a firewall issue, and it's also not because I'm connected to the same WiFi as the server. It's not a port forwarding issue either, as I've gone through all possible options. My router is a Fritzbox 6660, and there are no logs indicating that a request has even come through.
My second question is whether this is even allowed in Germany? Also, I've noticed that my ISP rarely changes my IP address; in fact, I haven't seen it change at all in the past few months, which is strange because in my home country, it changed every 24 hours.
Edit: First, thank you all for your help. I will try your suggestions over the course of this week or month (due to time-related issues :) and will report back with the results. Since I am clearly a noob when it comes to self-hosting and I plan to have only a Nextcloud server for personal use, what is the best way to secure the system in these situations and allow only certain devices to access it over the external network? (if I ever manage to access it at all)
Does your router indicate that you have DS-Light? I think O2 provides each customer DS-Light until they ask for a real IPv4.
To your second question: In case of DS-Light you don't need a new IPv4 IP every 24h because your IP is not public facing.
PS: I don't be sure, but the Fritz Remote Apps use IPv6 to ensure that they also work with DS-Light.