How to pass query string value in Irframe src

Hi forumian's 
I have a doubt in How to pass query string value in Irframe src
here is my code
 <asp:Label ID="lblrestid" runat ="server"  Text ='<%# Eval("RestId") %>' Visible="true" Font-Size="7pt"></asp:Label>    
<iframe id="voteframe" runat="server" height="175px"  frameborder="0" marginwidth="0" marginheight="0px"  scrolling="no" style="width: 195px " src="http://localhost/Sundarweb/opinion.aspx?ot='<%# Eval("RestId") %>'" >  </iframe>
From the above code
1) i have label with RestId
2) the same value i have to pass in iframe.
 
ISSUE to solve
i have to pass the RestId in that Iframe src.
the above is not working but if hardcode (see below ) Its working.
<iframe id="voteframe" runat="server" height="175px"  frameborder="0" marginwidth="0" ma ...