How to check if an IP is a proxy?

Question

proxy

Task: check if the site visitor is using a proxy.
Is such a test even possible? If yes, how to implement it?

Answer 1

differently you can
https://www.sans.org/reading-room/whitepapers/dete...

Answer 2

in theory, you can create a list of proxies and just check (you need to update it periodically). it is even better to set up auto-parsing of fresh proxies from some specialized resource

Answer 3

Check the headers (most http and https will disappear), try to go to some site using that address + popular ports. Check with the Internet [list of public proxies] (it will probably be difficult to manually, well, there are paid and free APIs). Some other proxies do not process certain html code well, according to these signs, too, can be calculated.

Answer 4

Scan ports, for example Zenmap