Single subdomain

You will probably want the site to have one adress for each page, not with and then without www. I tend to fix this by placing  following code snippet inside the Global.asax.cs file:

protected void Application_BeginRequest (object sender, EventArgs e)
{
   if (!Request.Url.Host.StartsWith ("www") && !Request.Url.IsLoopback)
   {
      var builder = new UriBuilder (Request.Url);
      builder.Host = "www." + Request.Url.Host;
      Response.StatusCode = 301;
      Response.AddHeader ("Location", builder.ToString ());
      Response.End ();
   }
}

This code will redirect the user to the www domain if they are currently accessing site without it.