An Overview Of IIS 7.5 Feature - Failed Request Event Buffering

This feature helps in troubleshooting performance, authentication, and 500 errors by collecting a trace of a web requests.

Let’s open IIS 7.5 manager and check whether FREB module is present or not under IIS section as shown below:



If it doesn't exist, we can install the same by going to “Turn on or off Windows Feature” in Control Panel and selecting the same under Internet Information Services, WWW Services, Health and Diagnostics, then click Tracing.



Let’s select “Default Web Site” and enable FREB by clicking on “Failed Request Tracing…” link Configure section under Actions pane:



Click on Enable, and select default path to save trace files of each failed web request and set limit for maximum number of trace files as 100.



Let’s create a trace rule to troubleshoot 404 issue on IIS. Double-click under Default Web Site and click on Add link under Actions pane.



Here, we can select the option to trace all requests or only ASPX or ASP page or custom page requests [using pattern]. Let’s select ASP.NET and click on Next.



Based on the above settings, it will collect traces of those requests meeting the condition.

We can specify specific status code or range of it to troubleshoot authentication and 500 issues. We can use time taken for troubleshooting performance issues like slowness and Severity field to trace all errors or warnings or critical errors only. Click Next.



Here, we will select trace providers. In our case, we will select ASPNET & WWW Server. Click FINISH:



We have created a rule to trace ASPX requests which have status code: 400-501 or time taken > 20 seconds.

Let’s create test.aspx and add the following code and browse it: