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)
Having been in this same position I think I can help, you are almost definitely being cgnat which means that you do not have your own ipv4. The two workarounds I used for this are to use only ipv6 which is public but means you can't always access it from older networks. And the second solution is to wireguard tunnel to a free oracle VM and use it as a proxy.
If you google it, you'll find lots of similar questions for O2. I think you have to contact their customer support and get that activated once.
And have a look at your IPv4 and IPv6 addresses. Sometimes you can do it via IPv6 already, just not over IPv4 because there is some translation in the way. (In case they want too much money to give you a real IPv4 address.)
Maybe you can try if you can open your FritzBox UI from the outside with your my.fritz address. I think that has IPv6 and a port forward in place (if activated).
And btw: It's perfectly fine to do it. People need storage and online collaboration. Access to their data while away.
Isn't myfritz plain old IPv6 directly to the router without any proxying or tunneling? If yes, communication would mean IPv6 packets make their way through the ISP to the router.
Do you have o2 DSL, o2 fiber, or o2 cable/coax Internet? O2 cable does not have a public IPV4 address by default, you need to request one from customer service.
You checked if you have a DS-Lite contract? Those are very popular. Especially with O2, Vodafone and the fiber ISPs.
The problem: You get only an IPv4 CG-NAT IP and a regular IPv6 IP. If your ISP (for example at work) did not configure an IPv6, you will not be able to connect (A and AAAA DNS records).
I assume you set up the port forwarding in your Fritzbox (under Internet > Freigaben > Portfreigaben)?
If it has the proper external port connected to your internal port it should connect.
I had the exact same problem and the solution was to ask my ISP who then either just gave me a public IP (Vodafone) or asked for money so my network could be reached from the outside (Primerocom). So check whether there is an option with you ISP to get a "public" IP.
The problem was with DS-Lite tunneling, as some users mentioned, and it only works over IPv6. However, now I have another issue. My entire family has access through their ISPs, but my cellular data ISP does not support IPv6. Is there any workaround that doesn't require me to look for a new ISP or asking for IPv4 address? 😀 By the way, thanks to everyone for the help!
Had the same issue. I have a VM at a hoster which proxies requests to my nextcloud server at home. Both the VM and my server on my home network are connected via tailscale. I've been using the VM for other stuff as well and happened to have it anyways, I didn't get one just for this purpose
Maybe I should first ask the cellular provider for IPv6, because I misspoke; they support it but haven't enabled it for me. If they provide it, then I won't currently have a need for IPv4, but thank you for the advice.