When acting in a reverse-proxy mode (using the ProxyPass directive, for example), mod_proxy_http adds several request headers in order to pass information to the origin server. These headers are:

X-Forwarded-For

The IP address of the client.

X-Forwarded-Host

The original host requested by the client in the Host HTTP request header.

X-Forwarded-Server

The hostname of the proxy server.

Be careful when using these headers on the origin server, since they will contain more than one (comma-separated) value if the original request already contained one of these headers. For example, you can use %{X-Forwarded-For}i in the log format string of the origin server to log the original clients IP address, but you may get more than one address if the request passes through several proxies.

See also the ProxyPreserveHost and ProxyVia directives, which control other request headers.

Note: If you need to specify custom request headers to be added to the forwarded request, use the RequestHeader directive.