FAQ.caslavka.cz - php: get IP address even if client is behind proxy

if (getenv("HTTP_CLIENT_IP")) {
    $ip = getenv("HTTP_CLIENT_IP");
} elseif (getenv("HTTP_X_FORWARDED_FOR")) {
    $ip = getenv("HTTP_X_FORWARDED_FOR");
} elseif (getenv("REMOTE_ADDR")) {
    $ip = getenv("REMOTE_ADDR");
}

or function:

function getIp () {
    if (getenv('HTTP_CLIENT_IP')) {       $ip['HTTP_CLIENT_IP']       = getenv('HTTP_CLIENT_IP'); }
    if (getenv('HTTP_X_FORWARDED_FOR')) { $ip['HTTP_X_FORWARDED_FOR'] = getenv('HTTP_X_FORWARDED_FOR'); }
    if (getenv('REMOTE_ADDR')) {          $ip['REMOTE_ADDR']          = getenv('REMOTE_ADDR'); }
    if (getenv('HTTP_USER_AGENT')) {      $ip['HTTP_USER_AGENT']      = getenv('HTTP_USER_AGENT'); }

    return $ip;
}