I've recently had the chance to configure ISA Server 2006(domain member) as L2TP/IPsec remote access VPN server with a Mac OS X 10.4.8 as L2TP/IPsec VPN client.
I've used certificates for IKE authentication(the CA was an Windows 2003 Enteprise CA).
I've almost completed an article regarding this. I will publish it as soon as possible.
In a future part, we will talk about using pre-shared keys too. Pre-shared keys are a weak authentication method, but they can be useful for testing.
I did not have the chance to configure ISA 2006 Server(domain member) as L2TP/IPsec remote access VPN server with a Mac OS X 10.5.x machine as L2TP/IPsec VPN client.
Installing a certificate for IKE authentication on a Mac OS X 10.4.8 machine was a little painful. I've played a little bit with a Mac OS X 10.5.x machine, and I've noticed that the installation of a certificate is an easier process. But, as said before, I did not have the opportunity to test the L2TP/IPsec VPN connection from an Mac OS X 10.5.x machine as VPN client with ISA Server 2006 as L2TP/IPsec VPN server.