public static IPAddress GetNetworkPrefix(this IPAddress address, NetMask mask)
{
if (address == null)
throw new ArgumentNullException(nameof(address));
if (mask == null)
throw new ArgumentNullException(nameof(mask));
if (address.AddressFamily != Sockets.AddressFamily.InterNetwork)
throw new NotSupportedException(OnlyIPv4Supported);
return mask & address;
}