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

Related Tutorials

---

• How to See and Flush the Contents of the DNS Resolver Cache in Vista
• How to Fix the Windows Live Messenger Unable to Sign In Error in Vista
• How to Change or Disable the QoS Reserved Bandwidth Limit in Vista
• 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

 

[pacinitaly]

thank shawn!!!! this works

1. Click Start. 2. Click All Programs. 3. Click Accessories. 4. Click Command Prompt. 5. On Command prompt type: cd.. (press Enter). Now do it again: cd.. (press Enter). 6. Now type the following commands (for each command dont forget to press Enter): netsh interface tcp set global autotuning=disabled netsh interface tcp set global chimney=disabled netsh interface tcp set global rss=disabled 7. Reboot your computer for the changes to take effect. 8. If you want to revert everything type the following commands: netsh interface tcp set global autotuning=enabled netsh interface tcp set global chimney=enabled netsh interface tcp set global rss=enabled 9. As usual reboot your system for the changes to take effect.

 

[Brink]

You're welcome Pacinitaly.

Shawn

 

[Ex_Brit]

Since SP2 some people are seeing those settings not sticking and the procedure to get around that is as follows:

In an elevated Command Prompt...click Enter after each line and to exit when finished type exit then click Enter twice over.

netsh
interface
tcp
set heuristics disabled
set global autotuninglevel=disabled

 

[Brink]

Thank you Peter. Tutorial has been updated for this.

 

[Ex_Brit]

Question, what ramifications, if any, are there from doing this?

 

[Brink]

By default, Vista in normal auto tuning level will use RWIN size of 256 bytes with a scale factor of 8. This value may not be suitable for older routers and servers which does not support the TCP scale factor, and continue to communicate with 65536 bytes. This can then cause a slow down in network speeds with auto tuning still set as normal. Routers and servers which do support the TCP scale factor, are usually better with auto tuning set to normal. I say play with it and test to see which setting may give you the best network speed or not.

 

[Ex_Brit]

Thanks. I haven't noticed any difference either way personally.

 

[Brink]

Yeah, usually the default settings are best unless you have one of these older devices.

 

[Yoranah]

Thank you i do it done.

 

[Brink]

You're welcome Yoranah, and welcome to Vista Forums.

 

[evomunk]

i'm trying to autotune my TCP/IP levels but i'm required to have "elevation"?

Microsoft Windows [Version 6.0.6002]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\evomunk>netsh interface tcp show global
Querying active state...

TCP Global Parameters
----------------------------------------------
Receive-Side Scaling State : enabled
Chimney Offload State : disabled
Receive Window Auto-Tuning Level : highlyrestricted
Add-On Congestion Control Provider : none
ECN Capability : disabled
RFC 1323 Timestamps : disabled
** The above autotuninglevel setting is the result of Windows Scaling heuristics

overriding any local/policy configuration.


C:\Users\evomunk>netsh interface tcp set global autotuninglevel=disabled

Set global command failed on IPv4 The requested operation requires elevation.


C:\Users\evomunk>netsh
netsh>interface
netsh interface>tcp
netsh interface tcp>set heuristics disabled

Set heuristics command failed on WSH The requested operation requires elevation.


netsh interface tcp>

 

[Brink]

Hello Evomunk, and welcome to Vista Forums.

You just need to open a elevated command prompt instead. (Run as administrator)

1. Open a elevated command prompt.

Hope this helps,
Shawn

 

[prothall]

Hi All, Firstly let me say great site, this speed up vista guide has been awesome.

Anyway on to my issue. After verifying my auto-tune setting at highly restricted and then going into command prompt with elevated mode, I have attempted to change my autotune setting to restricted, off etc, after entering commands specified and getting the "ok" and rebooting it still comes up as highly restricted. I am running home premium x64. I'm on ADSL2+ if that makes any difference. I managed to turn on chimney setting.

 

[Brink]

Hello Prothall, and welcome to Vista Forums.

You might see if setting it to normal first, then restrict may allow it not be high.

Hope this helps,
Shawn

 

[skillet]

I'm noticing a problem where I receive 35-50MB/sec over my intranet over 1gigabit but it sometimes slows down to 8MB/sec and sustains for the same test tasks.

If I reboot speed goes to 35-50 again.. Sometimes even logging out does it. I've noticed other people say they hit a 8MB/sec limit as well. Has anyone figured out what is limiting or causing it?

I'm loading an image sequence off of a server using a program to test throughput.

I've experimented with the different RSS settings and disabling it and it doesn't seem to make a difference. I also tried chimney offload but in netstat it isn't offloading anything.

Thanks!

 

[jeffrynov]

Omfg i disabled this it was set at high and i also disabled page clearing or whatever and yea but before i did this i was at around 13MBs download and 1MB upload. Now... IM AT 30MBs download!!! But still only 1MB upload. Thank you so much you seriously make me happy ^_^. Now i can tell my friends that i almost know for a fact my connection is better than theirs lol Also i disabled the reserved bandwidth. Thank you so much again!!!

Yes indeed you looked surprise but it doesn't mean your friends can not do the same thing as you did :D just don't tell them the secret our commander Brink told you about :D hehehee and have a Vista day !!

 

[skillet]

By the way, it's been a while now and I'm on windows7 now...but the issue was that the MMCS (Multimedia Class Scheduler) was slowing down the network speed when I had anything that was multimedia open... quicktimes usually or webpages. I did that hack where you remove the dependency it has on audio in your registry file and then stop the service. It wont let you before that because it has the audio dependency.

Anyways, what it does is slow your net connection down to make sure your quicktimes play smoothly and don't bog your cpu. Stupid idea in my opinion. Lets go slow all the time, to make sure your media doesn't skip. Obviously, it will only skip on slow computers. My 8 core doesn't have this problem.

 

[TomSawyer1977]

I been doing what it said and I get a message about ipv4 something unable to change.

 

[Brink]

Hello Tom,

Could you post a screenshot of what you are getting?

 

[TomSawyer1977]

Actually I got it thanks... I just need to know in plain english what is the highest setting???