How to know if an IP is external or not?

Question

I wish to detect if an address IP is local or external. In a web application, my customer wish to access files directly through samba on local network, and by a download link if you are not in the network.

I may just check if my IP is 172.30.*.*, but it won't work anymore if my customer switch to a 10.*.*.* or IPV6.

I may use a config var, so the customer may change it at will. I would like it to be automatic, with no config var.

How would you proceed ?

Answer 1

Update the list of IP ranges as you please. I haven't updated this list in awhile, but it should have most. Sorry, I never added IPv6 support to it.

function reserved_ip($ip)
{
    $reserved_ips = array( // not an exhaustive list
    '167772160'  => 184549375,  /*    10.0.0.0 -  10.255.255.255 */
    '3232235520' => 3232301055, /* 192.168.0.0 - 192.168.255.255 */
    '2130706432' => 2147483647, /*   127.0.0.0 - 127.255.255.255 */
    '2851995648' => 2852061183, /* 169.254.0.0 - 169.254.255.255 */
    '2886729728' => 2887778303, /*  172.16.0.0 -  172.31.255.255 */
    '3758096384' => 4026531839, /*   224.0.0.0 - 239.255.255.255 */
    );

    $ip_long = sprintf('%u', ip2long($ip));

    foreach ($reserved_ips as $ip_start => $ip_end)
    {
        if (($ip_long >= $ip_start) && ($ip_long <= $ip_end))
        {
            return TRUE;
        }
    }
    return FALSE;
}

var_dump(reserved_ip('127.0.0.1')); // reserved (localhost)
var_dump(reserved_ip('74.125.140.101')); // not reserved (Google)

Answer 2

Unfortunately, there is no easy way to determine this with certainty. See my comment for an interesting example.

In IPv4 world, you can try doing this: determine your server's external IP address (using, for example http://ip-address.domaintools.com/myip.xml) and compare it with the client's socket remote address ($_SERVER['REMOTE_ADDR']). If they are the same, then you are running on the same network, if they are different, then it's a different network.

In IPv6 world (properly deployed networks), there is no such thing as a private network and every device everywhere has its own public IP address. In this case, the only way to determine whether you're local or not is to maintain a full list of local devices.