I have hosting and domain like that:
www.EXAMPLE.com
I\'ve created few subdomains like that:
www.PAGE1.EXAMPLE.com
www.PAGE
This is something I have wanted to do with ASP.NET MVC for a long time, but... This is not a concern that ASP.NET MVC is responsible for. This is a server concern (IIS). What you need to do is allow for wildcard subdomains on your IIS server and point them to your one application.
Then you can do something like this with the HttpContext:
HttpContext.Current.Request.Url.Host // user1.yourwebsite.com
Then you just need to parse that and push it into your ASP.NET MVC app anyway you see fit:
The choice is really up to you.
Note: The downside here is that this makes local development increasingly difficult, so you might want to mock up a way to fake a subdomain in your application.