Troubleshoot HTTP 400 Bad Request error on IIS

There's an J2EE app running on the Tomcat with ISAPI redirector on IIS 8 of Windows Server 2012.
Yesterday the client got the error related to an AJAX request. When debugging the problem, I found out that the IIS returns HTTP 400 Bad Request error instead of passing along the url for the Tomcat to handle it.

In the IIS log file, there's no record for this request nor error log neither.

Go to the IIS admin:
Website >
Advanced Settings > Limits > Maximum URL Segments: 32
Request Filtering module > Edit Feature Settings:
Maximum URL Length: 4096
Maximum query string: 2048

Everything is fine. The url that makes error meets those configuration since it has just few segments and the length is around 380 characters - far behind the limit settings.

Then I tried to shorten the url a little bit and then a little bit.. and then finally it worked. It seems there's a limit around 300 characters.

Google around to enable the error log and I found How to troubleshoot HTTP 400 errors
Then go to  Error logging in HTTP APIs
Download the Enable HTTP API error logging  Microsoft Fix it 50634 to install it, but it said the current OS is not matched! Though the instruction applies for Windows Server 2012 Standard as the app is running on.

So have to go to regedit and configure the Http.sys registry settings with following parameters:
EnableErrorLogging: Decimal 1
ErrorLogFileTruncateSize: Decimal 10 (MB)
ErrorLoggingDir: C:\inetpub\logs\LogFiles

Then do : net stop http

It asks to confirm another services also:
   Windows Remote Management (WS-Management)
   Windows Event Collector
   World Wide Web Publishing Service

Then do: net start http
The HTTP Service service was started successfully.

Check the website, it's stopped!
Do  net start http again, but it said the http service is already started!

So go to the services manager to start World Wide Web Publishing Service, then Windows Remote Management (WS-Management) and Windows Event Collector

Then test again and see the error log file with a record just shows a very simple error reason: URL

Continue to read and go to Http.sys registry settings for IIS

Wow, there's a limit setting called UrlSegmentMaxLength with 260 characters by default! I thought that caused the problem because the full url with domain name that worked when there's around 300 characters.

So go to regedit and add UrlSegmentMaxLength with 1000 characters value to the HTTP parameters and restart http, w3svc, winrm and wecsvc services again.

Finally it worked!

I wonder why the MS didn't make it for a each specific website like the Maximum URL Segments and easily to set. But we'll have to configure in the Windows registry that requires to restart whole services and affect all sites.