User Control And Master Page ASP.Net

Default content will appear unless it is overridden in a particular content page.
File: Default.master
<%@ Master Language="C#" %>
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">


    Default Master


    
    
        
                            id="ContentPlaceHolder1"
                runat="server"/>
        

        
                            id="ContentPlaceHolder2"
                runat="server" />
        

        
                            id="contentAd"
                Runat="server">
                                    id="imgAd"
                    ImageUrl="~/BannerAd.gif"
                    CssClass="ad"
                    AlternateText="Advertisement"
                    Runat="server" />
            
        

        
    
    


File: DefaultContent.aspx
<%@ Page Language="C#" MasterPageFile="~/Default.master" %>
    ID="Content1"
    ContentPlaceHolderID="ContentPlaceHolder1"
    Runat="Server">
    Content in the first column
    Content in the first column
    Content in the first column
    Content in the first column
    Content in the first column

    ID="Content2"
    ContentPlaceHolderID="ContentPlaceHolder2"
    Runat="Server">
    Content in the second column
    Content in the second column
    Content in the second column
    Content in the second column
    Content in the second column