Pages inheritance

Have this in your web config file

<configuration>
  <system.Web>
    <pages masterPageFile="your master name.master" />
  </system.Web>
</configuration>

the

<system.web></system.web>

tag may be already exists, then only need to add the pages tag inside of it. Don't define a new System.Web tag

The above one is for .Net framework 4, some of the lower version may have this syntax

<pages master="your master.master"></pages>

Can have a master page inherited from a class inherited from master page.

In case of all the pages has to use a common base class, alternatively can have a class with extension methods for the Page class.

Example...

public static class PageExtensionMethods
{
    public static string GetDefaultCopyRightString(this Page globalPage)
    {
        return "Copy Right Reserved Test Company , 2011";
    }
}

Now you can call this method from any page i.e in all pages..example..

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
       string copyRight=this.GetDefaultCopyRightString();
    }
}