Using a windows system to connect to a L2TP VPN server while your behind a NAT router needs an regedit to work. (On Mac this is not needed.)

1. Open the Registry to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\IPSec
2. Create a new Dword (32Bit) value named: AssumeUDPEncapsulationContextOnSendRule
3. Change the Value of this Key to 2
4. Restart System before this takes effect.

• 0 It’s the default value. When it’s set to 0, Windows can’t establish security associations with servers located behind NAT devices.
• 1 When it’s set to 1, Windows can establish security associations with servers that are located behind NAT devices.
• 2 When it’s set to 2, Windows can establish security associations when both the server and VPN client computer (Windows Vista or Windows Server 2008-based) are behind NAT devices.