ExtensionlessUrlHandler causes 404 Not Found with default document on IIS - asp.net

Question

I recently updated some ASP.NET Nuget packages and modified the index.html file of my web site. Now I get 404-Not Found error but ONLY for the root path, i.e. when the web site address is typed without subdirectory or file name.
If I explicitly append "/index.html" then the default document is displayed correctly.
I also noticed that the line below in my web.config file has an unexpected behavior: If I remove the line, then the root path can be displayed, but the Web API requests return 404-Not Found response. If I keep it, then Web API requests work but the default document causes 404-Not Found.
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
The complete "handlers" section of web.config is as follows:
<handlers>
<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
<remove name="OPTIONSVerbHandler" />
<remove name="TRACEVerbHandler" />
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>
I made no changes to the default document setting or physical path file permissions. How can I fix this?

Answer 1

I just discovered that the problem has nothing to do with my modification in index.html. The actual cause originated from the way MVC routing works: I had just added MVC components to my project, and newly-added MVC route config started digesting all extensionless paths. As per this explanation, I just added an exception for the root path (the empty string), and the problem was fixed:
public class RouteConfig
{
public static void RegisterRoutes(RouteCollection routes)
{
routes.MapMvcAttributeRoutes();
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.IgnoreRoute("");
...
}
}