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.
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.
WORKAROUND
To work around this issue, do not use IPsec tunnel mode when the Windows Vista-based computer is behind an NAT device.
STATUS
This behavior is by design.
MORE INFORMATION
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
314764 Using Internet Protocol Security with Network Address Translation and Internet Security Acceleration Server
Vista IPSEC NAT-T Tunnel
Properties

Article ID: 944335 - Last Review: 01/16/2015 09:56:09 - Revision: 1.2

Windows Vista Enterprise 64-bit Edition, Windows Vista Home Premium 64-bit Edition, Windows Vista Ultimate 64-bit Edition, Windows Vista Business, Windows Vista Business 64-bit Edition, Windows Vista Enterprise, Windows Vista Home Premium, Windows Vista Ultimate

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