In ASP.Net, while uploading large files using FileUpload control, you may have experienced an error saying that "Maximum request length exceeded". The default value of Maximum upload file size is set to 4 MB. In most cases, this limit is set to avoid DDoS attacks, large file uploads and few other reasons. So, when you try to upload a file with the size larger than 4 MB, you will start seeing this error.

Server Error in '/' Application.
------------------------------
Maximum request length exceeded.

Solution :

machine.config file is set to 4MB default limit. We can change it to 20MB using the following code in the web.config.

< system.web >
  < httpRuntime executionTimeout="240" maxRequestLength="20480" / >
< /system.web >

For IIS 7 and later versions, we can modify the default upload limit to 30MB. You will need to add the following code to the web.config.

< system.webServer >
      < security >
           < requestFiltering >
                < requestLimits maxAllowedContentLength="3000000000" / >
           < /requestFiltering >
      < /security >
< /system.webServer >

Note:

maxAllowedContentLength is estimated in bytes
maxRequestLength is estimated in kilobytes.