PHP function to check if IP falls within a range

is_on_campus.php

<?php

function is_on_campus($IP = false) {

    // If no IP is passed grab it from $_SERVER[]
    $IP = $IP ? $IP : $_SERVER['REMOTE_ADDR'];

    // Convert IP to long integer
    $IPnum = ip2long($IP);

    // Test against (made up) campus IP ranges
    if (
        ( $IPnum >= ip2long( "111.11.11.11" ) && $IPnum <= ip2long( "111.11.11.22" ) ) ||
        ( $IPnum >= ip2long( "222.22.22.22" ) && $IPnum <= ip2long( "222.22.22.33" ) ) ||
        // made-up proxy server
        $IPnum === ip2long( "33.33.33.33" )
        )

    {
        return true;
    }

    else return false;
}

?>