I have an IPSec tunnel to a remote network. Works great!
I also have an internal L2TP server running on OS X which I want NATed in.
I can't seem to get them both to work together as they are both trying to
use port 500.
I tried using an optional interface for the L2TP server but that didn't
seem to work. I gave the interface an external IP (bridged with 'none')
and plugged it into my T1 gateway. No luck.
I have never been able to get PPTP to work properly on OS X (and I'm not
the only one) so I've given up on that.