routes.MapRoute(
      name: "monPrefix",
      url: "{action}.mon/{id}",
      defaults: new { controller = "login", action = "index", id = UrlParameter.Optional }
);

<modules runAllManagedModulesForAllRequests="true" />

public class loginController : Controller
    {
        public ActionResult index()
        {
            if (Session["userInfo"] == null)
            {
                return View();
            }
            else
            {
                return RedirectToAction("main");
            }
        }
     .
     .
     .
     .