Install Failed Request Tracing via Windows Features under Internet Information Services > Health and Diagnostics; 2. Enable it for a specific site in IIS Manager by clicking Enable in Failed Request Tracing; 3. Add rules by specifying request paths and status codes like 404,500 with Verbose level for detail; 4. Review generated XML logs in %SystemDrive%\inetpub\logs\FailedReqLogFiles\ using a browser or IIS Failed Request Viewer; 5. Optionally configure global settings in applicationHost.config for log directory and size, ensuring proper permissions and selective rule usage to manage log volume in production, which together provide comprehensive troubleshooting insight for failed web requests.

Enabling Failed Request Tracing in IIS (Internet Information Services) helps you diagnose issues with specific web requests—especially those that result in HTTP error codes like 404, 500, etc. It provides detailed logs showing each step of the request processing, which is useful for troubleshooting.

Here’s how to enable and configure Failed Request Tracing in IIS:

1. Install Failed Request Tracing (if not already installed)

By default, Failed Request Tracing might not be installed. You need to add it via Windows Features.

Steps:

• Open Server Manager (on Windows Server) or go to Control Panel > Programs > Turn Windows features on or off (on Windows 10/11).
• Navigate to:

  Internet Information Services > World Wide Web Services > Health and Diagnostics > Failed Request Tracing

• Make sure the checkbox is selected.
• Click OK to install.

2. Enable Failed Request Tracing at the Site Level

Once installed, you must enable tracing for the specific site.

Steps:

• Open IIS Manager.
• In the Connections pane, select the website you want to monitor.
• Double-click Failed Request Tracing in the main panel.
• Click Enable in the Actions pane on the right.

This creates a tracing folder under the site's directory (or logs folder) where log files will be stored unless configured otherwise.

3. Add Failed Request Tracing Rules

Tracing doesn’t log every request by default. You define rules based on status codes or request paths.

Steps:

• With your site selected, click Failed Request Tracing Rules.
• In the Actions pane, click Add…
• Configure the rule:
  • Request path: Use * to apply to all requests, or specify a file/path (e.g., *.aspx, /api/*).
  • Status codes: Enter the HTTP status codes you want to trace (e.g., 404, 500, or 404,500,502).
  • Verbosity Level: Choose Verbose for maximum detail (includes all events), or lower levels to reduce log size.

Click OK to save the rule.

4. Understanding the Logs

When a request matches your rule:

• IIS generates an XML log file in the configured directory (usually %SystemDrive%\inetpub\logs\FailedReqLogFiles\).
• Each file contains a timeline of events: authentication, URL rewriting, handler mapping, etc.
• You can open these XML files in a browser or use tools like Log Parser or IIS Failed Request Viewer (part of IIS Diagnostic Toolkit) for better readability.

5. Optional: Set Global Configuration (Advanced)

You can adjust global settings using applicationHost.config:

• Location: %windir%\system32\inetsrv\config\applicationHost.config
• Look for the <tracing> section.
• You can change log directory, maximum log file size, and other settings.

Example:

<tracing enabled="true" directory="D:\IISLogs\FailedRequests" />

Notes:

• Failed Request Tracing can generate a lot of data. Use rules selectively in production.
• Make sure the IIS application pool identity has write permissions to the log directory.
• For troubleshooting 500 errors, combine failed request logs with Windows Event Viewer and regular IIS logs.

That’s it. Once enabled and configured, you’ll get detailed insight into problematic requests. Just trigger the error (e.g., access a missing page), then check the logs.

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