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I am receiving event 789 when connecting to my Forefront TMG VPN server from windows 7 clients via L2TP. This does not occur on XP systems. I've run through the debugging at http://blogs.technet.com/b/rrasblog/archive/2009/08/12/troubleshooting-common-vpn-related-errors.aspx without success.

I'm receiving error 4976 server side with the following message. "During main mode negotiation, IPsec received an invalid negotiation packet." How can I resolve this?

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After investigation it appears that the issue is that RRAS is responding on the default IP address assigned to the external NIC (.100) versus the IP which the VPN is created on (.101). Attempting connection to .100 appears to have fixed the issue. Placing .101 as the default IP address on the NIC would also likely resolve the issue.

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