If you want users to always use www.yourdomain.com to connect to your website (rather than just yourdomain.com), you can add the following code to your global.asax:
protected void Application_BeginRequest( object sender, EventArgs e){
//check the request to make it starts with www
//and is not localhost (dev)
if (!Request.Url.Host.StartsWith( "www" ) && !Request.Url.IsLoopback)
{
//no ... redirect.
UriBuilder builder = new UriBuilder (Request.Url);
builder.Host = "www." + Request.Url.Host;
Response.Redirect(builder.ToString(), true );
}
}
This code will run at the beginning of every request, check the URL being used, and redirect to www.yourdomain.com. So that you can even use this on your local machine for testing, it also checks to see if it's localhost.