Configuring L2TP using PSK on Mac OS X is very easy thanks to a nice simple user interface. With Mac OS X 10.4, codenamed Tiger, it should also be possible to use L2TP with X.509 Certificates, although it is not always as straightforward as we might like.
To make things worse, all versions of Mac OS X up to at least version 10.4.3, which is Tiger with all software updates at the point of writing, have a broken NAT-T implementation. Openswan 2.4.5 has a workaround to correctly interoperate with the broken NAT-T implementation of Tiger.
Note
All versions of Mac OS X up to 10.4.3 (Tiger) have a broken NAT-T implementation. Openswan 2.4.1 has a workaround for this problem, but this workaround doesn't always work yet. Hopefully the workaround will work in all cases in Openswan 2.4.2 or 2.4.3.
To configure a L2TP/IPsec VPN connection, open the Internet Connect application from the System Preferences menu, or from the wireless menu that appears when you click on...