Question

Is there anyway in PHP to use uniquely identify a user’s router? I’d like t know what users are on the same router.

Answer 1

You can retrieve the users IP address using $_SERVER['REMOTE_ADDR'] and then use a traceroute utility to get the hops and check for the routers that you wish to find, if you know the IPs of both of them.

Assuming that the router is not address-translating for them, otherwise this will not work, as it relies on being able to get back through the router to the user. If either router can return to the user, then it will not work at all. Good for dial-in users though.

<?php
$ip = $_SERVER['REMOTE_ADDR'];
$router1IP = "123.123.123.123";

$output = array();
exec('traceroute -n ' . $ip, $output, $result);

if ($result == 0) {
    $outputText = implode("\n", $output);
    if (preg_match("/" . preg_quote($router1IP) . "/", $output)) {
        echo "Router 1";
    } else {
        echo "Router 2";
    }
}
?>