smr’s blog

env variable REMOTE_ADDR is used to get the ip address of the requesting system in http protocol. But if the end host sending its request through a proxy, then REMOTE_ADDR will have the ip of the proxy.
In that case the env variable HTTP_X_FORWARDED_FOR holds the ip of the host, for which the proxy is working for.

A simple cgi script to use it.
[ creates a access log file of the visiting ips(deeper than proxy ip) ]

fopen(FH, “>>access.log”);
if( $ENV{’HTTP_X_FORWARDED_FOR’} ){
print FH “$ENV{’HTTP_X_FORWARDED_FOR’} ( $ENV{’REMOTE_ADDR’} )”;
}else{
print FH “$ENV{’REMOTE_ADDR’}”;
}
close FH;

In squid, one can choose not to forward the ip of the host it is working for by setting the tag forwarded_for as off

This entry was posted on Thursday, June 30th, 2005 at 1:20 am and is filed under hacking. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.