Proxy Variables A proxy server can communicate with the other party via various variables, which actual IP address a request came from or whether a proxy server was used. Here is a small summary of the most important proxy variables: FORWARDED_FOR HTTP_X_FORWARDED_FOR HTTP_CLIENT_IP X_FORWARDED_FOR X_HTTP_FORWARDED_FOR A proxy server can use these variables to pass on the actual IP address of the client. HTTP_VIA HTTP_FORWARDED HTTP_PROXY_CONNECTION If one of these variables is set, the other party knows that you are using a proxy server. Elite Proxy or also L1 Proxy An elite proxy does not transmit the information that you are using a proxy server, nor does it transmit the IP address of the user. That's why servers of this type are in high demand. None of the proxy variables mentioned above are transmitted. Anonymous proxy or L2 proxy Proxy servers of this type tell the other party that a proxy server is being used, but not the IP address of the user. Some servers block requests from proxy servers, but most servers allow the requests and do not log them separately. At least one of the proxy variables from the lower block is transmitted. No variable is transmitted from the upper block. Transparent proxy or L3 proxy These proxy servers identify themselves to the other party as proxy servers and share the same IP address as the user. Since the user is not anonymous when using such a proxy server, these servers are less in demand. Mostly they are only used in a chain with anonymous or elite proxies.