Custom routes in MVC

Hi,

I am building my first MVC application and I need some advice on the routing. Right now my route looks like this:

            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );

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If I have an url that looks like this: www.site.com/Home/About it will go to the apropriate controller and run the Actionresult About().

Now, if I have an url that looks like this: www.site.com/Home/Something a resource not found message will be shown. I suppose this is standard behaviour - right?

I want to accomplish this: When the url contains an unknown part (Something in this case) I would like to run a specific ActionResult in the appropriate controller passing the unknown parameter so I can serve a view with data collected from my database - or serve my own view informing the user that the resorce doesn't exist. How do I set up this route?

Best regards
RTSol