Open a page in ModalPopUP

To Open a page in modal pop up   extender of ajax we have to use these source:

<ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="lnkPopup" PopupControlID="panOpen" BackgroundCssClass="ModalBackground" CancelControlID="btnCancel" PopupDragHandleControlID="panOpen" > </ajaxToolkit:ModalPopupExtender>

<asp:Panel ID="panOpen" runat="server" Height="400px" Width="400px" CssClass="ModalWindow">

<IFRAME id="frame1" src="SourcePage.Extension / URL of the external Site" Scrolling="auto">

</IFRAME>

<asp:Button ID="btnCancel" runat="server" Text="Close" />

</asp:Panel>

<a id="lnkPopup" runat="server">Show Popup</a>