ASP.NET MVC 404 handling and IIS7 <httpErrors>

Question

Good day!

I use strategy to handle 404 errors like this: http://stackoverflow.com/questions/3545906/error-handling-for-asp-net-mvc-2-and-iis-7-0 or this: http://stackoverflow.com/questions/619895/how-can-i-properly-handle-404s-in-asp-net-mvc/620559#620559

In short: I handle 404 as exception in Global.asax without adding any routing rules, if the exception is 404 I render special controller\action with error message.

On IIS6 it works with ASP.NET wildcard mapping. On IIS7 in integrated mode I need to add the following to the Web.config (where /error/HttpError404 is my action with 404 page):

    <httpErrors>
        <remove statusCode="403" subStatusCode="-1" />
        <remove statusCode="404" subStatusCode="-1" />
        <error statusCode="404" prefixLanguageFilePath="" path="/error/HttpError404" responseMode="ExecuteURL" />
        <error statusCode="403" prefixLanguageFilePath="" path="/error/HttpError403" responseMode="ExecuteURL" />
    </httpErrors>

Why? Routing works differently on IIS integrated mode and IIS6 wildcard mapping?

Thanks in advance!

UPDATE: According to my tests it seems that my error handling works and my 404 action is rendered, but it seems that IIS sees 404 response code (which I set programmatically in my 404 action) and replace my page with default errors.

When I set <httpErrors> I got two hits for 404 page: one from exception handling in Global.asax and one from IIS.

Can this be the cause?

Answer 1

It seems I have fixed it by setting in Web.config:

        <httpErrors existingResponse="PassThrough" />