Request Filtering is used for restricting the types of HTTP requests that processed by IIS 8. it help to prevent potentially harmful requests from reaching the server. The request filter module scans incoming requests and rejects requests that are unwanted based upon the rules that you set up.
If you have configured Request Filtering users will get this error "404 file or directory not found" when they try to access the blocked file name extension.
https://www.youtube.com/watch?v=Gw7ER0eeOqU
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