Mac OS X Server v10.5, 10.6: VPN - Some Windows clients may not be able to connect using L2TP (IPSec)
Some Microsoft Windows clients may not be able to connect to the Mac OS X Server VPN service if the Mac OS X Server is behind a NAT (Network Address Translation) router or firewall.
This article applies to Windows XP (SP2), Vista, and Windows 7 clients.
This article has been archived and is no longer updated by Apple.
You may need to modify settings on the Windows clients to allow access to the Mac OS X Server VPN service using L2TP (IPSec). By default, the Windows client may not be configured to allow NAT traversal. This is necessary to allow a connection to the Mac OS X Server VPN service when the server itself is behind a NAT router or firewall.
Please see the following Microsoft support articles:
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