Check if loop back is private network or a loopback address...

IsLoopbackOrPrivate.cs

static bool IsLoopbackOrPrivate([NotNull] IPAddress clientIp)
{
    // RFC for private networks:
    // http://www.faqs.org/rfcs/rfc1918.html

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

Source:

• https://stackoverflow.com/questions/8113546/how-to-determine-whether-an-ip-address-in-private