L2TP server does not respond properly from a CARP VIP
If you setup an L2TP server and try to connect to a CARP VIP on the same interface, it does not work. The server responds from the interface IP rather than the CARP VIP.
The PPTP server does not suffer the same limitation (though it is TCP, not UDP.)
Can be worked around by adding a port forward on the CARP VIP to the WAN IP for udp/1701.