What Are the Four Logging File Formats Indicated on the IIS Web Server?


Heather Bennett

When it comes to managing and analyzing web server logs, it is essential to understand the different file formats that can be generated by the Internet Information Services (IIS) web server. These log files provide valuable insights into the traffic and activities on your website, helping you identify issues, track user behavior, and optimize your site’s performance. In this article, we will explore the four main logging file formats indicated on the IIS web server.

IIS Log Format

The default log file format used by IIS is known as the W3C Extended Log File Format. This format is widely supported and provides comprehensive information about each request made to the web server.

It includes details such as the client’s IP address, date and time of the request, requested URL, status code returned by the server, and more. The W3C Extended Log File Format is highly customizable, allowing you to specify which fields to include in your log files.

NCSA Common Log File Format

An alternative logging format supported by IIS is the NCSA Common Log File Format. This format follows a simpler structure compared to the W3C format but still provides essential information about each request.

The NCSA format includes fields such as remote hostname (IP address), identity of authenticated users (if applicable), date and time of the request, requested URL, status code returned by the server, and more. While not as detailed as W3C format logs, NCSA logs are easier to parse and analyze.

IIS Binary Log File Format

The IIS Binary Log File Format offers a more efficient way of storing log data compared to text-based formats like W3C or NCSA. Instead of using plain text, binary log files store data in a compact binary format, resulting in smaller file sizes.

This format is particularly useful for high-traffic websites where log file size can become a concern. However, due to the binary nature of these logs, analyzing them requires specific tools or libraries designed to read and interpret the binary data.

ODBC Logging

The last logging file format available on IIS is ODBC Logging. This format allows you to log web server activity directly into a database using Open Database Connectivity (ODBC).

With ODBC logging, you can store your log data in a structured manner, enabling more advanced analysis and integration with other systems. ODBC logging provides flexibility in terms of the database backend and allows you to define custom tables and fields to suit your specific requirements.


In conclusion, understanding the different logging file formats indicated on the IIS web server is crucial for effectively managing and analyzing your website’s log files. Whether you choose the detailed W3C Extended Log File Format, the simpler NCSA Common Log File Format, the efficient IIS Binary Log File Format, or opt for ODBC Logging to store logs directly into a database, each format offers unique advantages depending on your needs. By leveraging these logging formats properly, you can gain valuable insights into your website’s performance and user behavior.

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