canonical domain

In the Global.asax file, add the following to the Application_BeginRequest() method.

void Application_BeginRequest(Object source, EventArgs e)
{            
   HttpApplication app = (HttpApplication)source;

   // IMPORTANT! Replace this with your domain name:
   string domainName = "thedomain.com";

   if (app != null)
   {
      string host = app.Request.Url.Host.ToLower();
      string requestUrl = app.Request.Url.PathAndQuery;

      if (String.Equals(host, domainName, StringComparison.CurrentCultureIgnoreCase))
      {
         Uri newURL = new Uri(app.Request.Url.Scheme +
                              "://www." + domainName);

         // This should match what is setup as the default document on the site
         if (requestUrl.ToLower() != "/default.aspx")
         {
            String dest = requestUrl.ToLower().Replace("default.aspx", "");
            newURL = new Uri(app.Request.Url.Scheme +
               "://www." + domainName + dest);
         }

         app.Context.Response.RedirectLocation = newURL.ToString();
         app.Context.Response.StatusCode = 301;
         app.Context.Response.End();
      }
   }
}