L2TP passthrough

Hello,

We have a VPN server on Windows 2008 R2.

The passthrough for the PPTP is working well.

But I can't make the L2TP passthrough working.

I have forwarded the 3 ports (500, 1701 and 4500) to the server.

And add a rule to allow the ESP protocol (50).

But it still not working.

Am I forgetting something ?

Thanks