how to set layout page when authentication true and false

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MVC3

i am working on mvc3. i set default rout in Gloabl.asax which is given below

routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Job", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);

This is the default rout of my project. i have also two layout page, one is page layout(_Layout.cshtml) and second is for login page(_login.cshtml). i just want to set when Request.IsAuthencated true then default route display with _Layout.cshtml and when Request.IsAuthencated false then _login.cshtml show be display. and i set in _ViewStart.cshtml is

@{
if

(Request.IsAuthenticated)
   {
       Layout = "~/Views/Shared/_Layout.cshtml";
   }
   else
   {
       Layout = "~/Views/Shared/Login.cshtml";
   }

}

please help how can i do this. please help