Article ID: 944335 - Last Review: November 6, 2007 - Revision: 1.2

The connection fails on a Windows Vista-based computer when you try to communicate with another computer through an IPsec tunnel-mode connection

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SYMPTOMS

On a Windows Vista-based computer, when you try to communicate with another computer through an Internet Protocol security (IPsec) tunnel-mode connection, the connection fails.

This issue occurs if the Windows Vista-based computer is behind a Network Address Translation (NAT) device.

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CAUSE

This is a design change in Windows Vista.

Behind an NAT device, if more than one computer shares the same source port, a conflict may occur. Therefore, Windows Vista removes support for tunnel mode when the computer is behind an NAT device.

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WORKAROUND

To work around this issue, do not use IPsec tunnel mode when the Windows Vista-based computer is behind an NAT device.

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STATUS

This behavior is by design.

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MORE INFORMATION

For more information, click the following article number to view the article in the Microsoft Knowledge Base:

314764 (http://support.microsoft.com/kb/314764/ ) Using Internet Protocol Security with Network Address Translation and Internet Security Acceleration Server

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