IP Address headers (Remote_Addr) - When is this header sent by the browser?

Question

I want to know when a browser includes the header - Remote_Addr in the HTTP request. I observed the request sent by the browser on loading stackoverflow.com, in the web console window of Firefox. There were no headers pertaining to IP address sent. So, does this mean the browser never sends this header along with a HTTP request?

Answer 1

In client-server applications, the IP address of the client (i.e., the browser) is sent via the socket connection (the request) to the server (e.g., Apache). If the client is using a proxy server however, that may be the proxy's IP address instead of the client's IP.

Remote_Addr is an ENV returned by the server and available to server-side scripts/applications, not the client browser.

In PHP, you can use something like $_SERVER['REMOTE_ADDR'] to obtain the IP address of the client. In Perl you can use something like $ENV{'REMOTE_ADDR'};