There are also several other methods that often work, e.g. the X-Forwarded-For HTTP header if there is a local proxy, or a long list of non-HTTP protocols or tu

There are also several other methods that often work, e.g. the X-Forwarded-For HTTP header if there is a local proxy, or a long list of non-HTTP protocols or tunnel-XYZ-inside-HTTP protocols that have the client IP as part of the protocol. Temporary IPv6 addresses actually solve this, especially for P2P systems that do benefit from knowing the client IP in case there is a peer on the same LAN, because the address they get is the same one the remote server sees (no additional information) and then it's both a valid local address but hard to correlate with anything when every device can have hundreds of them at once.