Add folder to all URLs in an ASP.net MVC 5 site - asp.net-mvc

Question

I have an MVC 5 site with this structure:
example.com
example.com/area1 (index for whole section)
example.com/area2/item5 (specific item for section)
For SEO reasons I'd like to change every URL to this:
example.com/keyword (redirected from example.com)
example.com/keyword/area1
example.com/keyword/area2/item5
The keyword is fixed and always the same, though at some point in the future there may be a site with the same structure but different content with a different keyword in. That is probably at least a few months off though.
What is the quickest / easiest way to implement the above. Being able to get the name of keyword would be an advantage later though isn't essential right now.
I could use attribute routing, though I'd have to update A LOT of ActionMethods to do this - and most currently don't even use attribute routing.
thx.
Update
I've tried adding the below to RouteConfig.cs, but none of the Url's work for some reason:
routes.MapRoute(
name: "Default",
url: "keyword/{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);

Answer 1

public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
string keyword = "keyword";
// keyword route - it will be used as a route of the first priority
routes.MapRoute(
name: "Defaultkeyword",
url: "{keyword}/{controller}/{action}/{id}",
defaults: new
{
controller = "Home",
action = "Index",
id = UrlParameter.Optional,
keyword = keyword
});
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
}
also you need to add this Defaultkeyword route with few changes into your Area1AreaRegistration.cs file
public override void RegisterArea(AreaRegistrationContext context)
{
context.MapRoute(
"Area1_defaultKeyword",
"{Keyword}/Area1/{controller}/{action}/{id}",
new { Keyword = "Keyword", controller = "HomeArea1", action = "Index", id = UrlParameter.Optional }
);
context.MapRoute(
"Area1_default",
"Area1/{controller}/{action}/{id}",
new { action = "Index", id = UrlParameter.Optional }
);
}