Avoid content page postback when master page dropdownlist value changed

Question

I am running one asp.net application where i have one master page and content page. In master page i am using update panel inside dropdownlist. Now when i am running application then when i change dropdownlist value then first content page postback event fired after that master page postback event fired.

Below is my master page update panel with dropdown:

<asp:UpdatePanel runat="server" ID="updLOB" UpdateMode="Conditional">
     <ContentTemplate>
       <asp:DropDownList ID="ddl1" runat="server" OnSelectedIndexChanged="ddl1_SelectedIndexChanged" AutoPostBack="true">
      <asp:DropDownList>
      </ContentTemplate>
 </asp:UpdatePanel>

How do i avoid content page postback when dropdown list changed?

Answer 1

<asp:UpdatePanel runat="server" ID="updLOB" UpdateMode="Conditional">
     <ContentTemplate>
       <asp:DropDownList ID="ddl1" runat="server" 
OnSelectedIndexChanged="ddl1_SelectedIndexChanged" AutoPostBack="true">
      <asp:DropDownList>
      </ContentTemplate>
 <Triggers>
  <asp:AsyncPostBackTrigger ControlID="ddl1" 
     EventName="SelectedIndexChanged" />
   </Triggers>
 </asp:UpdatePanel>