In ASP.NET 2.0, managing controls has become easier. Instead of declaring them on every page, you can declare them only once in your web.config file and use them in your entire project.
<configuration>
<system.web>
<pages>
<controls>
<add tagPrefix="portal" tagName="Top"src="~/Controls/Top.ascx" />
</controls >
</pages >
</system.web>
</configuration>
Once you have registered this control in your web.config, you can use this control on any page without explicitly adding a register directive on the page.
<body>
<form id="form1" runat="server">
<div>
<portal:Top ID="Top1" runat="server" />
</div>
</form>
</body>