how to identify remote machine uniquely in php?

Question

how to identify remote machine uniquely in proxy server environment, i have used $_SERVER['REMOTE_ADDR'] but all machines in proxy network has same IP Address, is there any way

Answer 1

Don't ever depend on information that is coming from the client. In this case, you're running up against simple networking problems (you can never be sure the client's IP address is correct), in other cases the client may spoof information on purpose.

If you need to uniquely identify your clients, hand them a cookie upon their first visit, that's the best you can do.