Starting with Windows Vista, there were improvements made to the network stack including a little known feature called TCP Window Auto-tuning. The auto-tuning feature allows newer versions of Windows to be able to adjust the RWIN value automatically on the fly so to speak. While it does offer improvements in certain realms, it can also cause network performance issues. I wanted to detail a few scenarios of TCP Auto-tuning slow network performance and when I have observed this issue come into play
- Receive Window Auto-tuning Level Normal
- Auto Tuning Level Windows 10
- Receive Window Auto-tuning Level Experimental
- Fixes an issue in which the TCP receive window autotuning feature in a TCP connection stops working. This issue occurs in Windows Server 2008 R2 and in Windows 7 environments. The TCP receive window autotuning feature does not work correctly in Windows Server 2008 R2 or in Windows 7.
- Window Auto Tuning Like much of the Windows 10 operating system, the Window Auto Tuning feature built into the software was created with only the best of intentions. It’s actually a modern version of a feature that has been around since the days of Windows Vista that is designed to improve the way that certain programs perform when sending.
![Windows Auto Tuning Level Windows Auto Tuning Level](/uploads/1/3/4/4/134411141/628737765.png)
And a bug found in Windows: It is very clear that when Windows was asked to display the current 'Receive Window Auto-Tuning Level' and Windows said 'normal' and claimed that 'is the result of Windows Scaling heuristics overriding any local/policy configuration on at least one profile'- that Windows displayed the wrong mode, and should have. Receive Window Auto-Tuning Level is set to normal. To disable Receive Window Auto-Tuning Level, click Start, and in the Search box type 'command.' In the results, right-click Command Prompt, and then click Run as administrator. At the command prompt, run the following command: netsh int tcp set global autotuning=disabled For more information, see.
You can see your current TCP Auto-tuning values by issuing the NETSH command:
It will display something similar to the following (the following clip is taken from a Windows 10 workstation):
If you notice above, the line Receive Window Auto-Tuning Level is set to normal. This is the default setting out of the box.
To turn off TCP Auto-tuning you can use the following command:
Another option is to set TCP Auto-tuning to highlyrestricted which seems to have the same performance improving effect as disabling when connecting to legacy OS versions.
TCP Auto-tuning slow network performance
For the most part, I have seen the TCP Auto-tuning slow network performance issue come into play with new server OS’es and client OS’es talking to legacy server OS’es like Windows Server 2003. Especially in file copies, RDP sessions and SQL query performance the issue has been evident.
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Slow File copy and RDP performance
In particular I have seen many cases where the file copies from newer operating systems to slower operating systems and back have been super slow. Recently, in an environment still running a Windows 2003 server, RDP from Windows 10 was horribly slow. The experience was one of the mouse freezing every 5 seconds or so for 2 or 3 seconds then it would release and keep doing that – basically an unusable state.
Slow SQL query performance
Recently, in working with a developer who was running queries from Windows 2012 R2 server running SQL 2012, he had horrible query performance querying data from an old Windows 2003 server running SQL 2005. You may be saying to yourself, Windows 2003 and SQL 2005 are not supported any longer, why would anyone be running those operating systems still? Sad to say, they are still out there in greater numbers than we would like to think, mainly due to legacy applications that are bound in some way to an older version of SQL/Windows for whatever reason.
Case in point, the query performance you see in the first screenshot is taken with the auto-tuning levels set at default. Notice the msDur value in the first query. These values are connecting back to a legacy Windows 2003 server.
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Now, the following screen clip is taken showing the query performance after turning auto-tuning off. Also, these values are connecting between sites so this is why they are still showing as much higher than the other query results you see.
Final Thoughts
If you are chasing a weird network performance issue that seems to have no other explainable cause, you may want to check into your TCP Auto-tuning settings. The TCP Auto-tuning slow network performance issue can be a difficult issue to track down especially since it is usually the last thing we think to look at. If you have a mix of legacy OS and new OS versions in your environment, it is a good bet you may want to focus on and test various settings with Auto-tuning to rule out any potential issues with network performance.
The Receive Window Auto-Tuning feature lets the operating system continually monitor routing conditions such as bandwidth, network delay, and application delay. Therefore, the operating system can configure connections by scaling the TCP receive window to maximize the network performance. To determine the optimal receive window size, the Receive Window Auto-Tuning feature measures the products that delay bandwidth and the application retrieve rates. Then, the Receive Window Auto-Tuning feature adapts the receive window size of the ongoing transmission to take advantage of any unused bandwidth.
While the feature may improve speed, in some cases it can also cause problems and slow down the network.
To disable the feature, use this command:
Receive Window Auto-tuning Level Normal
To see if the feature is enabled or disabled, use this command:
To enable the Receive Window Auto-Tuning Level, use this command:
Auto Tuning Level Windows 10
Here’s a list of available options for the autotuning parameter:
Receive Window Auto-tuning Level Experimental
disabled: Fix the receive window at its default value.
highlyrestricted: Allow the receive window to grow beyond its default value, but do so very conservatively.
restricted: Allow the receive window to grow beyond its default value, but limit such growth in some scenarios.
normal: Allow the receive window to grow to accommodate almost all scenarios.
experimental: Allow the receive window to grow to accommodate extreme scenarios. WARNING: This can dramatically degrade performance in common scenarios and should only be used for research purposes. https://yellowattorney254.weebly.com/auto-tune-engineer-video.html.
highlyrestricted: Allow the receive window to grow beyond its default value, but do so very conservatively.
restricted: Allow the receive window to grow beyond its default value, but limit such growth in some scenarios.
normal: Allow the receive window to grow to accommodate almost all scenarios.
experimental: Allow the receive window to grow to accommodate extreme scenarios. WARNING: This can dramatically degrade performance in common scenarios and should only be used for research purposes. https://yellowattorney254.weebly.com/auto-tune-engineer-video.html.
https://yellowattorney254.weebly.com/rca-output-not-recognized-by-traktor-pro.html. And check if it helps.Frequently Asked Questions: Windows 10Keep us posted on the issue to assist you better. Follow these steps to run the troubleshooter.Click Start.Type Troubleshooting in the search bar and press “Enter”.In the “Troubleshooting” window, click on“View All” on the left pane.Click on “ Hardware and Devices”.Click on “Advanced” and then click on “ Run as Administrator”.Click “ Next” and follow the on-screen instructions to complete the troubleshooting process.If you want to roll back to the previous operating system. I request you to refer the sectionHow to: Rollback to a previous version of Windows 10.