$client = $_SERVER['HTTP_CLIENT_IP']; $forward = $_SERVER['HTTP_X_FORWARDED_FOR']; $remote = $_SERVER['REMOTE_ADDR'];
What is the difference between HTTP_CLIENT_IP and HTTP_X_FORWARDED_FOR? – it is impossible to say. Different proxies may implement these, or may not. The implementations may vary from one proxy to the next, and they may not. A lack of a standard breeds question marks.
If more than one proxy was involved – the X-Forwarded-For: header might then contain a complete track of the forwarding chain, whereas the Client-IP: header would contain the actual client IP. This is pure speculation, however.