title: What is the difference between HTTP_CLIENT_IP and HTTP_X_FORWARDED_FOR?
body: <p>I understand that a header <code>HTTP_X_FORWARDED_FOR</code> is set by proxy servers to identify the ip-address of the host that is making the HTTP request through the proxy. I've heard claims that the header <code>HTTP_CLIENT_IP</code> is set for similar purposes.</p>
  
  <ol>
  <li>What is the difference between <code>HTTP_CLIENT_IP</code> and <code>HTTP_X_FORWARDED_FOR</code>?</li>
  <li>Why would one have different values than the other?</li>
  <li>Where can I find resources on the exact definition of these headers.</li>
  </ol>