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| Vista Tutorial - Auto Tuning - TCP/IP receive level Auto Tuning - TCP/IP receive level
How to Enable or Disable the Receive Window Auto Tuning Level in Vista
Published by Brink
06-21-2007
| | 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. |  | 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.
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| How To See Current Auto Tuning Settings |
1. Open a elevated command prompt. NOTE: For how, see: How to Open a Elevated Command Prompt in Vista 2. Click on Continue in the UAC prompt. 3. In the command prompt, type netsh interface tcp show global and press Enter. (See screenshot below)  4. Close the command prompt when done. 5. Run through the steps below to see if you have a TCP/IP Auto Tuning issue | STEP ONE: |
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| How to Restrict Auto Tuning |
1. Open a elevated command prompt. NOTE: For how, see: How to Open a Elevated Command Prompt in Vista 2. Click on Continue in the UAC prompt. 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 netsh interface tcp set global autotuninglevel=restricted and press Enter. (See screenshot below)
B) You will get a OK response if successful. If not, repeat step 3A.
C) Go to step 5.  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 netsh interface tcp set global autotuninglevel=high and press Enter. (See screenshot below)
B) You will get a OK response if successful. If not, repeat step 4A.  5. Close the command prompt window and restart the computer to apply the changes. 6. If it fixed your problem stop here. If not, continue to Step Two below. | STEP TWO: |
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| 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. NOTE: For how, see: How to Open a Elevated Command Prompt in Vista 2. Click on Continue in the UAC prompt. 3. In the command prompt, type netsh interface tcp set global autotuninglevel=disabled and press Enter. (See screenshot below) 4. You will get a OK response. If not, repeat step 3.  5. Close the command prompt and restart computer to apply the changes. 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. | STEP THREE: |
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| 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. NOTE: For how, see: How to Open a Elevated Command Prompt in Vista 2. Click on Continue in the UAC prompt. 3. In the command prompt, type: netsh interface tcp set global autotuninglevel=normal and press Enter. (See screenshot below) 4. You will get a OK response if successful. If not, repeat step 3.  5. Close the command prompt and restart the computer to apply the changes. That's it,
Shawn |  Published by | | | Administrator Join Date: Apr 2007 Location: Texas, USA
Posts: 23,752
Rep Power: 150 | |
 Tutorial Tools | | |
 Applies to | | All Vista Versions | | 64 Bit & 32 Bit | |
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04-16-2008
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| | Member vista home premium 32 bit The Underverse
Rep Power: 10
 | Re: Auto Tuning - TCP/IP receive level Im stuck on what to do with this, i ran the cmd and the command; netsh interface tcp show global but my recieve window auto-tuning level says "highlyrestricted" What does this mean?? any advice on what i should do? thanks. | My System Specs | | OS vista home premium 32 bit
04-16-2008
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| | Administrator Vista x64 Ultimate SP2 Texas, USA | Re: Auto Tuning - TCP/IP receive level 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 | My System Specs | | System Manufacturer/Model Number Custom OS Vista x64 Ultimate SP2 CPU Core2 Quad Q9450 2.66GHz 12MB Motherboard Gigabyte X48-DQ6 Memory 8 GB (4x2) DDR2 PC2-8500 1066 MHz Patriot Extreme Graphics Card BFG GeForce 9600 GT OC 512MB Sound Card Realtek HD Audio ALC889A Integrated Chip Monitor(s) Displays 28" Hanns-G HG281DJB and 17" eMachines E17T4 Screen Resolution 28" 1920x1200 and 17" 1280x1024 Keyboard Microsoft Wireless Multimedia Keyboard 1.1 Mouse Microsoft Standard Wireless Optical Mouse PSU Antec NeoPower 500 Watt Case Tagan El-Diablo Full Tower Cooling 250 mm Front, 360 mm Side, stock CPU, 120 mm SiLenX Rear Hard Drives 64GB Patriot SSD (v2)
750GB Samsung HDD HD753LJ SATA 32MB Internet Speed 3382 kb/s Download and 312 kb/s Upload Other Info Creative WebCam Instant
05-14-2008
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| | Newbie
Rep Power: 9
 | Re: Auto Tuning - TCP/IP receive level This is exactly what I needed.
I was transferring files from my home server to my main rig with Vista newly installed and was getting slooow speeds of ~12MBps on a GigE network. I tried the high setting and I got an immediate boost to 42MBps which is good but not as good as the ~52MBps I was getting in XP Pro.
I decided to try the disabled setting figuring that it would not net me much if anything. Lo and behold I got the fastest speeds I've seen on my LAN, 67MBps! I'm impressed.
Thanks for the tut! Great site BTW. | My System Specs | |
05-14-2008
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| | Administrator Vista x64 Ultimate SP2 Texas, USA | Re: Auto Tuning - TCP/IP receive level You're welcome Fam Money, and welcome to Vista Forums.
That's a good little jump.
Shawn | My System Specs | | System Manufacturer/Model Number Custom OS Vista x64 Ultimate SP2 CPU Core2 Quad Q9450 2.66GHz 12MB Motherboard Gigabyte X48-DQ6 Memory 8 GB (4x2) DDR2 PC2-8500 1066 MHz Patriot Extreme Graphics Card BFG GeForce 9600 GT OC 512MB Sound Card Realtek HD Audio ALC889A Integrated Chip Monitor(s) Displays 28" Hanns-G HG281DJB and 17" eMachines E17T4 Screen Resolution 28" 1920x1200 and 17" 1280x1024 Keyboard Microsoft Wireless Multimedia Keyboard 1.1 Mouse Microsoft Standard Wireless Optical Mouse PSU Antec NeoPower 500 Watt Case Tagan El-Diablo Full Tower Cooling 250 mm Front, 360 mm Side, stock CPU, 120 mm SiLenX Rear Hard Drives 64GB Patriot SSD (v2)
750GB Samsung HDD HD753LJ SATA 32MB Internet Speed 3382 kb/s Download and 312 kb/s Upload Other Info Creative WebCam Instant
05-14-2008
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| | da Cleaner Vista Home Premium 64bit Cambridge, UK | Re: Auto Tuning - TCP/IP receive level Would this help with gaming at all? | My System Specs | | System Manufacturer/Model Number Self built OS Vista Home Premium 64bit CPU Intel E8400 3GHz Motherboard Intel DX48BT2 Memory Kingston PC3-10666 4Gb Graphics Card XFX 9800 GTX XXX Sound Card Soundblaster X-Fi XtremeMusic Monitor(s) Displays 2x Samsung SM-T220HD 22" Screen Resolution 1680x1050 on two monitors Keyboard Dell Multimedia Enhanced USB Mouse Razer Diamondback 3G PSU Thermaltake ToughPower 850w Case Thermaltake Armor Cooling Tuniq Tower 120 Hard Drives WD Raptor X 150Gb
WD Raptor 36gb
3x Samsung F1 1Tb Internet Speed 8128/832 Other Info Thermaltake Muse esata caddy
05-15-2008
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| | Administrator Vista x64 Ultimate SP2 Texas, USA | Re: Auto Tuning - TCP/IP receive level Hi Swarfega,
It may if you run a networked game through a network device that doesn’t support RFC 1323 “TCP Extensions for High Performance”.
Otherwise, most likely it will not.
Shawn | My System Specs | | System Manufacturer/Model Number Custom OS Vista x64 Ultimate SP2 CPU Core2 Quad Q9450 2.66GHz 12MB Motherboard Gigabyte X48-DQ6 Memory 8 GB (4x2) DDR2 PC2-8500 1066 MHz Patriot Extreme Graphics Card BFG GeForce 9600 GT OC 512MB Sound Card Realtek HD Audio ALC889A Integrated Chip Monitor(s) Displays 28" Hanns-G HG281DJB and 17" eMachines E17T4 Screen Resolution 28" 1920x1200 and 17" 1280x1024 Keyboard Microsoft Wireless Multimedia Keyboard 1.1 Mouse Microsoft Standard Wireless Optical Mouse PSU Antec NeoPower 500 Watt Case Tagan El-Diablo Full Tower Cooling 250 mm Front, 360 mm Side, stock CPU, 120 mm SiLenX Rear Hard Drives 64GB Patriot SSD (v2)
750GB Samsung HDD HD753LJ SATA 32MB Internet Speed 3382 kb/s Download and 312 kb/s Upload Other Info Creative WebCam Instant
05-15-2008
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| | Member Ultimate SP1 x64 & x86 Paris | Re: Auto Tuning - TCP/IP receive level | Quote: | swarfega |  | | | Would this help with gaming at all? | | | | | Apparently when Windows Vista is connected to high speed broadband Internet connection, there may be some incompatibilities and conflict problem occuring lags in games.
It is reported sometimes that disabling auto tuning resolves this lag problem.
I just don't know as i only play chess on line | My System Specs | | OS Ultimate SP1 x64 & x86
05-15-2008
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| | da Cleaner Vista Home Premium 64bit Cambridge, UK | Re: Auto Tuning - TCP/IP receive level lol chess hehe, thanks | My System Specs | | System Manufacturer/Model Number Self built OS Vista Home Premium 64bit CPU Intel E8400 3GHz Motherboard Intel DX48BT2 Memory Kingston PC3-10666 4Gb Graphics Card XFX 9800 GTX XXX Sound Card Soundblaster X-Fi XtremeMusic Monitor(s) Displays 2x Samsung SM-T220HD 22" Screen Resolution 1680x1050 on two monitors Keyboard Dell Multimedia Enhanced USB Mouse Razer Diamondback 3G PSU Thermaltake ToughPower 850w Case Thermaltake Armor Cooling Tuniq Tower 120 Hard Drives WD Raptor X 150Gb
WD Raptor 36gb
3x Samsung F1 1Tb Internet Speed 8128/832 Other Info Thermaltake Muse esata caddy
05-30-2008
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| | Newbie Vista Home Premium x86, Vista Ultimate x86
Rep Power: 8
 | Re: Auto Tuning - TCP/IP receive level Should I be concerned if my auto tuning is disabled? I've used a few tweak programs prior to reading this. Just curious to know. Thanks! | My System Specs | | OS Vista Home Premium x86, Vista Ultimate x86 | Tutorial Tools | | | | Display Modes | Linear Mode | Vista Forums is an independent web site and has not been authorized, sponsored, or otherwise approved by Microsoft Corporation. "Windows Vista", the Start Orb, and related materials are trademarks of Microsoft Corp. © Designer Media Ltd Tutorial powered by GARS 2.1.8m ©2005-2006
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