Set Default Button in ASP.NET

<form id="form1" runat="server" defaultbutton="Button1">

   <asp:TextBox ID="Textbox1" runat="server" />

   <asp:TextBox ID="Textbox2" runat="server" />

   <asp:Button ID="Button1" runat="server" Text="Submit" />

   <asp:Button ID="Button2" runat="server" Text="Cancel" />

</form>