how to determine whether an IP address in private?

Question

So far I have this code:

NetworkInterface[] adapters = NetworkInterface.GetAllNetworkInterfaces();

foreach (NetworkInterface adapter in adapters)
{
  IPInte         


        

Answer 1

Added IPv6 and localhost cases.

    /* An IP should be considered as internal when:

       ::1          -   IPv6  loopback
       10.0.0.0     -   10.255.255.255  (10/8 prefix)
       127.0.0.0    -   127.255.255.255  (127/8 prefix)
       172.16.0.0   -   172.31.255.255  (172.16/12 prefix)
       192.168.0.0  -   192.168.255.255 (192.168/16 prefix)
     */
    public bool IsInternal(string testIp)
    {
        if(testIp == "::1") return true;

        byte[] ip = IPAddress.Parse(testIp).GetAddressBytes();
        switch (ip[0])
        {
            case 10:
            case 127:
                return true;
            case 172:
                return ip[1] >= 16 && ip[1] < 32;
            case 192:
                return ip[1] == 168;
            default:
                return false;
        }
    }