Network connectivity fails when you try to use Windows Vista behind a firewall device

Problem description

When you try to use a Windows Vista-based computer behind a firewall device, and you try to make a non-HTTP network connection, the network connection fails. When the network connection fails, the following programs may crash or respond slowly:

Microsoft Outlook or Windows Mail
Web browsers, such as Windows Internet Explorer 7
Remote Desktop Connection (RDC)
File sharing programs

When Outlook is affected by this issue, you receive the following message in a remote procedure call (RPC) dialog box:

Outlook is trying to retrieve data from the Microsoft Exchange Server Exchange_Server_FQDN. Or, you may see a "Trying to Connect" message in the status bar.This issue may occur if the firewall device has a problem with handling the Receive Window Auto-Tuning feature in Windows Vista. This article helps you work around this problem.

Workaround

To work around this problem, use one of the following methods:

Method 1. Disable auto-tuning and determine whether Windows scaling is handled correctly by the firewall device

To have us disable auto-tuning for you, go to the "Fix it for me" section. If you would rather disable auto-tuning yourself, go to the "Let me fix it myself" section.

Fix it for me

To disable auto-tuning automatically, click the Fix this problem link. Then, click Run in the File Download dialog box, and follow the steps in this wizard.

Note this wizard may be in English only; however, the automatic fix also works for other language versions of Windows.Note If you are not on the computer that has the problem, you can save the automatic fix to a flash drive or to a CD, and then you can run it on the computer that has the problem. Now go to the "Did this fix the problem?" section.

Let me fix it myself

To disable auto-tuning, follow these steps:

Click Start , click All Programs, and then click Accessories.
Right-click Command Prompt, and then click Run as Administrator. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
At the command prompt, type the following command, and then press ENTER:

netsh interface tcp set global autotuninglevel=disabledThis command disables the Receive Window Auto-Tuning feature.
Close the Command Prompt window.
Restart the computer.

Now go to the "Did this fix the problem?" section.

Did this fix the problem?

Try to make a non-HTTP network connection. That is, use the program that was affected by the problem.
If the problem is fixed, contact the manufacturer of the firewall device for steps to resolve the issue. If the problem is not fixed, you can contact support.
You can keep auto-tuning disabled until the problem is fixed. When you are ready to enable auto-tuning, click Start , click All Programs, click Accessories, and then click Command Prompt.
At the command prompt, type the following command, and then press ENTER:

netsh interface tcp set global autotuninglevel=normalThis command enables Receive Window Auto-Tuning again so that you can take advantage of the increase in network throughput performance that this option provides.

We would appreciate your feedback. To provide feedback or to report any issues with this solution, please leave a comment on the "Fix it for me" blog, or send us an e-mail message. For information about how to contact the manufacturer of the firewall device, visit the following Microsoft Web site:

http://support.microsoft.com/gp/vendorsMicrosoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

Method 2. Run the Internet Connectivity Evaluation Tool

The Internet Connectivity Evaluation Tool checks your Internet router to see whether it supports certain technologies. The tool is intended to be run from a home network behind a home Internet (NAT) router. Running this tool from behind a corporate firewall or on operating systems other than those specified in the "Applies to" section will not produce accurate results. This tool requires administrator credentials to run.

Cause

This issue may occur if the firewall device has a problem with its implementation of the TCP Window Scale Option that is defined in Internet Engineering Task Force (IETF) Request For Comments (RFC) 1323. By default, the Receive Window Auto-Tuning feature in Windows Vista uses a Window Scaling factor of 8 for non-HTTP connections. This issue does not occur when you try to make an HTTP connection.

More information

The following list describes some firewall devices that may experience this issue together with the cause of the issue on the device:

Linksys RV series (RV042, RV081, RV-16)
NetApp Cache Appliances NC 6.0.2 or an earlier versionThe TCP splicing feature may not work together with the Window Scaling feature in Windows Vista. By default, the TCP splicing feature is enabled on NetApp Cache Appliances NC 6.0.2 or on an earlier version.
Cisco PIX 6.1(5), Cisco PIX 6.2(3), and Cisco PIX 6.3(1) These devices do not support the Window Scaling feature in Windows Vista.
Cisco IOS Software ReleaseCisco IOS Software Release 12.3(15) and later versions of this software support the Window Scaling feature in Windows Vista.
Sonicwall The Window Scaling feature in Windows Vista may not work if you enable either of the following features on a Sonicwall firewall device:
- Strict TCP Enforcement Option
- Enforce strict TCP compliance with RFC 793 and RFC 1122
Checkpoint NG R55To work around this issue, disable the Sequence Verifier Enforcement feature.

For more information about the Receive Window Auto-Tuning feature in Windows Vista, visit the following Microsoft Web site:

http://technet.microsoft.com/en-us/magazine/cc162519.aspxThe third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.