What is my IP address ?

Your IP address is:

How can you determine my IP address ?

I can read your IP address from server variable $_SERVER['REMOTE_ADDR']

Note: this can be IP address of proxy server, you must examine other details to recognize that.

How do I get my IP address details ?

Details of your IP address are in server variable $_SERVER['HTTP_X_FORWARDED_FOR']

Note: variable $_SERVER['HTTP_X_FORWARDED_FOR'] is optional and need not to be set or can be empty.

How do I recognize I am behind proxy server ?

If $_SERVER['HTTP_X_FORWARDED_FOR'] is set and it is not IP from private network, you are behind proxy.

Note: Anonymous proxies are used to mask your true IP address, but with $_SERVER['HTTP_X_FORWARDED_FOR'] it may be found anyway.

How to recognize private network ?

On both IPv4 and IPv6 it is set of reserved adresses, see: http://en.wikipedia.org/wiki/Private_network

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