You can attach content pages to a master page at three levels:
1. page level
<%@ Page Language="C#" MasterPageFile="MySite.Master" %>
2. Application Level: By making a setting in the pages element of the application's configuration file
<pages masterPageFile="MySite.Master" />
3. At the folder level : This strategy is like binding at the application level, except that you make the setting in a Web.config file in one folder only