My ISP provide me with good IPv6 connection with support of opening ports how I like. But IPv4 is behind a CGNAT and makes me unable to host a service on the legacy Internet.
Unfortunetely some of my friends I want to host (Jellyfin and Nextcloud) for does not have modern Internet connection, so I have to put some proxy.
Now I need suggestions of a solution. VPN on some VPS they would need to connection to is one of them, but it should be as simple for them to use as possible.
Be careful with doing this. X-Real-IP and X-Forwarded-For are good for when the client is a trusted proxy, but can be easily faked if you don’t whitelist who’s allowed to use those headers. Somebody with IPv6 access could send “X-Real-IP: 127.0.0.1” or something and if the server believes it then you’ll see 127.0.0.1 in logs and depending on what you’re running the user may gain special permissions.
Also be careful with the opposite problem. If your server doesn’t trust the proxy, it will show the VPS IP in logs, and if you’re running something like fail2ban you’ll end up blocking your VPS and then nobody will be able to connect over IPv4.
Fair enough yeah. :)
The OP can solve that potential security issue with this option: https://nginx.org/en/docs/http/ngx_http_realip_module.html#set_real_ip_from on the local server nginx:
http { (...) real_ip_header X-Real-IP; set_real_ip_from [2a03::aaaac::1]; # Replace with the VPS IPv6 address. }This will make sure only the VPS is allowed to override the real IP.