Best way to implement a 404 in ASP.NET

I'm trying to determine the best way to implement a 404 page in a standard ASP.NET web application. I currently catch 404 errors in the Application_Error event in the Global.asax file and redirect to a friendly 404.aspx page. The problem is that the request sees a 302 redirect followed by a 404 page missing. Is there a way to bypass the redirect and respond with an immediate 404 containing the friendly error message?

Does a web crawler such as Googlebot care if the request for a non existing page returns a 302 followed by a 404?

Solution 1:

Handle this in your Global.asax's OnError event:

protected void Application_Error(object sender, EventArgs e){
  // An error has occured on a .Net page.
  var serverError = Server.GetLastError() as HttpException;

  if (serverError != null){
    if (serverError.GetHttpCode() == 404){
      Server.ClearError();
      Server.Transfer("/Errors/404.aspx");
    }
  }
}

In you error page, you should ensure that you're setting the status code correctly:

// If you're running under IIS 7 in Integrated mode set use this line to override
// IIS errors:
Response.TrySkipIisCustomErrors = true;

// Set status code and message; you could also use the HttpStatusCode enum:
// System.Net.HttpStatusCode.NotFound
Response.StatusCode = 404;
Response.StatusDescription = "Page not found";

You can also handle the various other error codes in here quite nicely.

Google will generally follow the 302, and then honour the 404 status code - so you need to make sure that you return that on your error page.

Solution 2:

You can use the web.config to send 404 errors to a custom page.

    <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
        <error statusCode="403" redirect="NoAccess.htm" />
        <error statusCode="404" redirect="FileNotFound.htm" />
    </customErrors>

Solution 3:

Easiest answer: don't do it in code, but configure IIS instead.

Solution 4:

I also faced with 302 instead 404. I managed to fix it by doing the following:

Controller:

public ViewResult Display404NotFoundPage()
        {
            Response.StatusCode = 404;  // this line fixed it.

            return View();
        }

View:

Show some error message to user.

web.config:

<customErrors mode="On"  redirectMode="ResponseRedirect">
      <error statusCode="404" redirect="~/404NotFound/" />
</customErrors>

Lastly, the RouthConfig:

routes.MapRoute(
             name: "ErrorPage",
             url: "404NotFound/",
             defaults: new { controller = "Pages", action = "Display404NotFoundPage" }
         );