How do sites like 2ipc.om.ua calculate the local IP of a PC behind NAT and Firewall?

Question

Computer networks

Interested in one thing, how to close from such systems? And what should be read to understand?

Answer 1

Disable javascript.
The site you provided calculates via webrtc

Answer 2

https://en.wikipedia.org/wiki/X-Forwarded-For

Answer 3

there is such a wonderful pppoe technology. Install Mikrotik with Internet access. raise vpn from mikrotik to vpn service in afghanistan (for example) (it’s not clear why they didn’t start such a service. it’s cooler than drugs. try to find out from the taliban who paid vpn. =D). and inside your home network you cling through the pppoe server to the Mikrotik itself. and you issue addresses from a pool of a city network of provider. Here you have "like anonymity".