Auto Tuning - TCP/IP receive level

How to Enable or Disable the Receive Window Auto Tuning Level in Vista​

   Information

The TCP receive window size (RWIN) is the amount of data that a TCP receiver (your computer) allows a TCP sender (other internet or local network computer) to send before having to wait for an acknowledgement. After the connection is established, the receive window size is advertised in each TCP segment. Advertising that maximum amount of data that the sender can send is a receiver-side flow control mechanism that prevents the sender from sending data that the receiver cannot handle. A sending host can only send at a maximum the amount of data advertised by the receiver before waiting for an acknowledgment and a receive window size update. Auto Tuning adjusts the receive windows size continually based upon the changing network conditions. This usually happens if you have a network device (EX: Router, modem, etc.) that doesn’t support RFC 1323 “TCP Extensions for High Performance”.

   Note

The TCP window size field controls the flow of data and is limited to between 2 and 65,535 bytes, and cannot be expanded anymore. Thus, a scaling factor is used to get a larger TCP receive window size to achieve more efficient use of high bandwidth networks. The TCP window scale option is used to increase the maximum window size from 65,535 bytes to 1 Gigabyte. Scaling up to larger TCP congestion window sizes is a part of what is necessary for TCP Tuning.

When dealing with slow network performance in Vista, the problem may be due to the above mentioned TCP Window Scaling option, where many older routers and and packet firewalls do not properly implement TCP Window Scaling (doesn’t support RFC 1323), and rewrite the window scaling factor during a transmission, and causing sending and receiving sides to assume different TCP window sizes. The situation causes malfunction Internet connection, non-stable traffic that is very slow, or network connection that is only available intermittently.

Beside, Windows Vista enhances further TCP window scaling with auto tuning feature, where TCP stack in Vista system will auto tune and adjust the RWIN size to increase the percentage of full-sized TCP segments that are used during bulk data transmission based on the network scenario it encountered. And thus it’s no longer possible to specify a custom size for the TCP/IP Receive Window (RWIN) size with the inclusion of new auto tuning feature, unless the application it self uses SO_RCVBUF. However, Vista TCP auto tuning feature may get things wrong sometimes. Instead of optimal true receive window size, incompatible and out of range RWIN size may be used.

By default, Vista in normal auto tuning level will use RWIN size of 256 bytes with a scale factor of 8. This value is not suitable for all routers and servers which does not support TCP scale factor, and continue to communicate with 65536 bytes.

UPDATE: An Update on Windows TCP AutoTuningLevel - Windows 10 Forums

   Tip

Possible TCP/IP Auto Tuning Related Problems:

• Indefinite delay (hang) when opening the Certificate Services snap-in.
• Slow (sometimes no) group policy application.
• Trying to select a domain user in order to add that principal to a local security group (the object picker) would hang indefinitely.
• Instant Messaging is not working well. Sometimes not at all by not being able to sign in.
• Access to local file servers (EX: networked drives, etc.) are extremely slow and sometimes did not succeed at all (appears to hang).
• Internet connection problems.
• Extremely slow file transfers.
• Other strange unexplained network connecting issues.
• Wireless network connection problems
• Website browsing and downloads are extremely slow.

FIRST

How To See Current Auto Tuning Settings

1. Open a elevated command prompt.​

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2. Click on Continue in the UAC prompt.​

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3. In the command prompt, type in bold belowand press Enter. (See screenshot below)​

netsh interface tcp show global​

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4. Close the command prompt when done.​

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5. Run through the steps below to see if you have a TCP/IP Auto Tuning issue​

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STEP ONE

How to Restrict Auto Tuning

1. Open a elevated command prompt.​

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2. Click on Continue in the UAC prompt.​

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3. To Restrict Auto Tuning​

NOTE: Allows for the receive window to grow beyond the default value of 65,535 bytes, but limits such growth in some scenarios.​

A) In command prompt, type in bold below and press Enter. (See screenshot below)​

netsh interface tcp set global autotuninglevel=restricted​

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B) You will get a OK response if successful. If not, repeat step 3A.​

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C) Go to step 5.​

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4. To Highly Restrict Auto Tuning​

NOTE: Allows for the receive window to grow beyond the default value of 65,535 bytes, but doing so very conservatively. In this mode, Vista will by default use a RWIN of 16,384 bytes with a scale factor of 2.​

A) In the command prompt, type in bold below and press Enter. (See screenshot below)​

netsh interface tcp set global autotuninglevel=high​

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B) You will get a OK response if successful. If not, repeat step 4A.​

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5. Close the command prompt window and restart the computer to apply the changes.​

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6. If it fixed your problem stop here. If not, continue to Step Two below.​

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STEP TWO

How to Disable Auto Tuning

NOTE: Disables the autotunning feature in Vista completely, and sets and locks the RWIN receive window to the default value as 65536 bytes.

1. Open a elevated command prompt.​

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2. Click on Continue in the UAC prompt.​

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3. In the command prompt, type in bold belowand press Enter. (See screenshot below)​

netsh interface tcp set global autotuninglevel=disabled​

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   Note

You can also type in bold below and press enter after each command:

   Note

• netsh
• interface
• tcp
• set heuristics disabled
• set global autotuninglevel=disabled
• exit

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4. You will get a OK response. If not, repeat step 3.​

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5. Close the command prompt and restart the computer to apply the changes.​

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6. If it fixed your problem stop here. If not, you may not have a issue with Auto Tuning and will need to turn it back on. Continue to Step 3 below.​

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STEP THREE

How to Enable Auto Tuning Back to Normal Default

NOTE: This turns Auto Tuning back to the default on (Normal) setting in Vista. Allows for the receive window to grow to accommodate almost all scenarios. See NOTE at the top of the tutorial for more on this.

1. Open a elevated command prompt.​

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2. Click on Continue in the UAC prompt.​

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3. In the command prompt, type in bold below and press Enter. (See screenshot below)​

netsh interface tcp set global autotuninglevel=normal​

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   Note

You can also type in bold below and press enter after each command:

   Note

• netsh
• interface
• tcp
• set heuristics enabled
• set global autotuninglevel=normal
• exit

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4. You will get a OK response if successful. If not, repeat step 3.​

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5. Close the command prompt and restart the computer to apply the changes.​

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That's it,
Shawn

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---

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• How to Create a Local Area Network Connection Status Shortcut in Vista
• How to Create a Network Connections Shortcut in Vista
• How to Enable or Disable the Chimney Offload State in Vista

 

[hispanico]

I Brink this is my situation:

I have vista ultimate 32bit. My connection is FastWeb 6Mbit and my son play a lot in internet like quake, cod4 etc...which is the best configuration to have good and high connection ??

Thank a lot
Hyspa

 

[Brink]

Hello Hyspa, and welcome to Vista Forums.

The settings you have are the default settings and usually do a great job set that way. As a test you can see how your network runs with the Receive Window Auto-Tuning Level (Livello regolazione automatica finestra ricezione) set with the steps in the tutorial to see if it may be better with one of them instead. If no, just set back to the default Normal setting.

Hope this helps,
Shawn

 

[panais]

Hi Mafia_Boy,

That just means that you had ran Step One in the tutorial to restrict the TCP/IP Auto tuning. If you want the normal settings again, run Step Three.

Hope this helps,
Shawn

Would this help with (utorrent slows my internet)?
Because everytime i start utorrent my internet sloooows.
With Bitcomet everything works fine Bitcomet doesn't slow my internet.
How and why is that?

 

[Brink]

Hi Panais,

You could try the setting set either way to test to see for sure, but it is most likely a setting in the utorrent program that is not set for optimum performance. You should post a new thread in the Software or Network & Internet forum about this program to see what others may recommend for it's settings.

Hope this helps,
Shawn

 

[mohanmathew]

I have a similar problem with my Vista Ultimate. It takes nearly 1 minute or more to connect to my wireless point. At the same time other laps in my house can be connected instantly. Mine is lenovo, and others are Sony and Dell. The problem is mainly when the lap resumes a hibernated session, not when it starts as usual. If I try to diagnose the problem, some times it may connect and some times it may not and I need to restart the wifi router. I didn't tried the Auto tuning session, have to try when I reach home.

 

[Brink]

Let us know how it went MohanMathew.

 

[mohanmathew]

At present my setting is like shown below screenshot.

I tried to change it, but it showing an error

How can I overcome this?

 

[Brink]

MohanMatthew,

You would just need to open a elevated command prompt instead from step 1. Right click on the Command Prompt shortcut and click on Run as administrator.

 

[mohanmathew]

Yes, I changed it. Now the connection seems fast. I have noticed the wireless connection after hibernation, it was instant!!

Thank You soo much

 

[Brink]

You're welcome. I'm happy to hear that it is faster for you now.

Shawn

 

[antonyua]

Brink,
I am using Vista home Premium Os And i want to configure my internet conection to run faster ... so I tried to change the Receive Window Auto-Tuning Level From restricted ( Default Setting ) To Disable it and to normal... But i dont see any Diffrence I am Using A dell laptop And connectin wireless to my modem that is in the same Room so i dont think the problem may be in Signal ... my Adsl ISP Provider Is Forthnet (Greek Provider ) and They Says that they provide me 24mb Down / 1mb up But i never seen these speed neither in my Laptop nor in my desktop PC that is connected Lan with the Modem... So i am wondering How some others getting faster speed conections ... Here are a Speed Test I made :

And It not getting Over 10 mb Down
Also i have mad Full Bandwidth Back from the QoS Reserved Bandwidth Limit...
My Moden Also says that it connected to Internet with 16 mb Down / 1mb up .. . ( D Link DSL G624t )


So what maybe the reason of Low internet connection

 

[Brink]

Hello Antonyua,

It's mostly related to a router or network adapter issue instead of just the bandwith for their issues.

 

[antonyua]

So I Cant do Anything For Increasing the Speed ?? :D

 

[Brink]

Not unless you had a issue with a router or network adapter that this tutorial could help with, or unless you pay your ISP more $$$ for a faster connection.

Sorry

 

[antonyua]

Ok Thanks Anyway :D

 

[Brink]

You're welcome.

 

[Pain1349]

Good day!

I found that my Auto tuning level was set as highlyrestricted. So I gave it a try and disabled it and my bootup and reboots were slower than before noticeably. Then I re enabled it but set to normal, and now it reboots alot quicker than before levels. I don't think it helped net speeds, but just thought I'd share this. although I didn't try to game online... cheers!

 

[Brink]

Thank you Pain1349 for posting back your results. Welcome to Vista Forums.

Shawn

 

[Gizmo-guy]

This Past August at a LAN Party I was hosting I had network issues. I was playing a MP3 from a buddy's PC before hosting a game of COD4. Everyone was having lag problems but me since I was running the server, so I turned on my other PC and ran a dedicated server, problem gone for everyone, but now I was having issues! I came across I very small article in Computer Power Users talking of Vista networking issues when playing media through windows media player before gaming on a network. Followed the article on how to fix it. After finding this thread a few days ago I looked at my recieve window auto-tuning level, and it was Restricted (I believe it said SeverelyRestricted). I have seen no impact of changing this other than gaming. I wanted to share this info after reading a few post, hope this helps.

 

[Brink]

Thank you Gizmo-guy for sharing your results. I'm sure that they will help others. Welcome to Vista Forums.

Shawn