Sometimes you may get the IP of the ISP Cache Server which of course you do not want.  To make sure you get the correct IP Address, the following may help:  
 
   if (getenv('HTTP_X_FORWARDED_FOR') {  
       $ip   = getenv('HTTP_X_FORWARD_FOR';  
       $host = gethostbyaddr($ip);  
   } else {  
       $ip   = getenv('REMOTE_ADDR';  
       $host = gethostbyaddr($ip);  
   }
 
 
 
 
http://www.php.net/manual/en/print [...] efined.php
 
 
 
voili
 
 
EDIT : pitit complément
 
 
Finally, note that any user can add an X-Forwarded-For header themselves. The header is only good for traceback information, never for authentication. If you use it for traceback, just log the entire X-Forwarded-For header, along with the REMOTE_ADDR.