title: HTTP Headers: What is the difference between X-FORWARDED-FOR, X_FORWARDED_FOR and HTTP_X_FORWARDED_FOR?
body: <p>I see various spellings of the non-RFC "XFF" HTTP header used for identifying the IP addresses the request has been forwarded through. Is there a difference between these different header names: <code>X-FORWARDED-FOR</code>, <code>X_FORWARDED_FOR</code>, and <code>HTTP_X_FORWARDED_FOR</code>? Do I need to look for all three?</p>
  
  <p>PS - Yes, I know this header can be easily spoofed :)</p>