Only LDAP client can get both L2TP and PPTP in Mountain Lion VPN service. Local client will only get L2TP and not PPTP.
So you have to configure your server with proper DNS and Open Directory and create Local Network User.
DNS will be very sensitive as you may facing problem to start Server Apps if the configuration is wrong.
Sorry for thread jumping,
I am troubleshoting an osx vpn system right now and was wondering since you mentioned it; whats the difference in AUTH MECH when a user is hosted local or within ldap ?
are there certain Auth mechs that are only supported via LDAP ? My L2TP clients get access using CHAP. is there a possibility CHAP is not supported under Shadow ?