[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode, Pack = 4)]
internal struct RasDialParams
{
    public int dwSize;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.RAS_MaxEntryName + 1)]
    public String szEntryName;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.RAS_MaxPhoneNumber + 1)]
    public String szPhoneNumber;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.RAS_MaxCallbackNumber + 1)]
    public String szCallbackNumber;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.UNLEN + 1)]
    public String szUserName;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.PWLEN + 1)]
    public String szPassword;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = RasConstants.DNLEN + 1)]
    public String szDomain;

    public int dwSubEntry;

    public IntPtr dwCallbackId;

    public int dwIfIndex;
}

public static uint RasDial(string entry, string user, string password, Form msgWindow, out IntPtr hRasConn)
    {
        RasDialParams dp;

        dp.dwSize = Marshal.SizeOf(typeof(RasDialParams));
        dp.szEntryName = entry;
        dp.szPhoneNumber = "";
        dp.szCallbackNumber = "";
        dp.szUserName = user;
        dp.szPassword = password;
        dp.szDomain = "";
        dp.dwSubEntry = 0;
        dp.dwCallbackId = IntPtr.Zero;
        dp.dwIfIndex = 0;

        var notifierType =
            msgWindow == null
                ? 0
                : 0xffffffff;

        var notifier =
            msgWindow == null
                ? IntPtr.Zero
                // Windows 10
                : msgWindow.Handle;
                //: msgWindow.Hwnd;

        var result = RasImports.RasDial(IntPtr.Zero, IntPtr.Zero, ref dp, notifierType, notifier, out hRasConn);

        if (result == RasError.ERROR_INVALID_SIZE)
        {
            dp.dwSize = (int)Marshal.OffsetOf(typeof(RasDialParams), "dwIfIndex");
            result = RasImports.RasDial(IntPtr.Zero, IntPtr.Zero, ref dp, notifierType, notifier, out hRasConn);
        }

        return result;
    }