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Is your client request missing from IIS log?

One can enable IIS logging by going to IIS Manager and checking the Enable logging checkbox. So, it means if IIS logging is enabled, then each and every request made by the client should be showing up in the IIS log. Isn’t it? But by any chance, if the request is not present in IIS log then the most probable reason would be either IIS was not running or may be request was not made.

But this statement is not 100% correct. Because whenever any request is made to the server, first it routes through HTTP.SYS then it comes to IIS. So, if anything is not visible under IIS logs, then one can see the logging for HTTP.SYS which is HTTPERR. The most common errors logged here are related to timeout or service unavailability.

The next question would be, where these logs are exactly saved?
You can find HTTPERR under C:\Windows\System32\LogFiles\HTTPERR

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