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Slow downloads and disconnects with Vista and Windows 7 - Receive Window Auto-Tuning

SystemSystem Member, NoReporting Posts: 178,019 Arc User
We had this conversation at work several years ago when I was providing tier 3 network security support.

Vista and Windows 7 have changed some TCP settings that weren't found in XP and older TCP implementations. One thing that popped into my head was the receive window auto-tuning feature and how it would conflict with some CheckPoint firewalls we had in place internally between sites.

A quick way to check to see if this "feature" is causing you grief is to change the setting via command prompt.

Run the command prompt in administrator mode by going to Start -> Programs -> Accessories right click on Command Prompt and choose Run as administrator

Restrict autotuning by running “netsh interface tcp set global autotuninglevel=restricted” from the command prompt.
Reboot your PC.

If all else fails, in order to disable this feature, run "netsh interface tcp set global autotuninglevel=disabled".
Reboot your PC.

In order to reenable autotuning, run “netsh interface tcp set global autotuninglevel=normal”.

Receive Window Auto-Tuning on Vista.
http://blogs.msdn.com/wndp/archive/2007/07/05/receive-window-auto-tuning-on-vista.aspx
Older routers and firewalls however do not handle window scaling correctly leaving the option in the original SYN packet but setting the connection’s scale factor to zero. Seeing the option on, the receiver responds with its own window scale factor. Believing that its scale factor has been accepted, the initiator scales the window appropriately while the receiver thinks that a scale factor of zero is applied and thus a small window of data should follow. As a result, the communication is slow at best. Sometimes, small window packets are dropped by the routers, essentially breaking the connection.

The resulting slow data transfers or loss of connectivity, users may experience as slow or hung networking applications. Remote Desktop Connection and network file copy are two scenarios particularly hurt by misbehaving routers.

If your connection from a Vista machine appears slow or hung, here are some steps to isolate the cause:

* First, make sure that your firewall and router can support window scaling. Some devices from Linksys, Cisco, NetApp, SonicWall, Netgear, Checkpoint, D-Link were reported as having problems with window scaling. (Some of the incompatible devices are given here. You can check with the manufacturer or run the connectivity diagnostic suite (especially, TCP High Performance Test) provided by Microsoft to determine your gateway device’s compliance.
* Second, check with the manufacturer if a firmware update has been issued for your device that can fix the problem. Replace the problematic device or update the firmware as suggested by the manufacturer. If the router cannot be replaced or if it the device is remote (e.g., a firewall of your ISP or corporation)
* Third, If the problem still persists, you can restrict autotuning by running “netsh interface tcp set global autotuninglevel=restricted” from the command prompt. We have found that restricted mode will often allow some of the benefits of autotuning with a number of problematic devices.
* Lastly, if all else fails, in order to disable this feature, run "netsh interface tcp set global autotuninglevel=disabled".
* (In order to reenable autotuning, run “netsh interface tcp set global autotuninglevel=normal”.)

How to disable the TCP autotuning diagnostic tool
http://support.microsoft.com/kb/967475
When the receive window autotuning feature is enabled, older routers, older firewalls, and older operating systems that are incompatible with the receive window autotuning feature may sometimes cause slow data transfer or a loss of connectivity between Vista clients. When this occurs, users may experience slow performance. Or, the applications may crash. These older devices do not comply with the RFC 1323 standard. Some device manufacturers provide software that works around the hardware limitations.
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