routes.MapRoute("Default", "{controller}/{action}/{id}",
new { controller = "Home", action = "Index", id = "" });
protected override void HandleUnknownAction(string actionName) {
//your code here.
}
routes.MapRoute("default-action", "{controller}/{actionName}/{id}", new {action="DefaultAction"});
public ActionResult DefaultAction(string actionName, string id) {
//handle default action
}