Draytek Vigor 3200 Series User Manual page 241

When you choose L2TP over IPSec (Must), you will see the following graphic:
Available settings are explained as follows:
Item
Profile Name
VPN Dial-Out Through
Always On
Pre-Shared Key
Description
Type a name for such profile. The length of the file is limited
to 10 characters.
Use the drop down menu to choose a proper WAN interface
for this profile. This setting is useful for dial-out only.
WAN1 First / WAN2 First / WAN3 First / WAN4 First /
WAN5 First - While connecting, the router will use
WAN1/WAN2/WAN3/WAN4/WAN5 as the first channel for
VPN connection. If WAN1/WAN2/WAN3 /WAN4/WAN5
fails, the router will use another WAN interface instead.
WAN1 Only / WAN2 Only / WAN3 Only / WAN4 Only/
WAN5 Only - While connecting, the router will use
WAN1/WAN2/WAN3/WAN4/WAN5 as the only channel for
VPN connection.
Check to enable router always keep VPN connection.
IKE Authentication Method usually applies to those are
remote dial-in user or node (LAN to LAN) which uses
dynamic IP address and IPSec-related VPN connections such
as L2TP over IPSec and IPSec tunnel.
Pre-Shared Key- Specify a key for IKE authentication.
Confirm Pre-Shared Key-Confirm the pre-shared key.
231 Vigor3200 Series User's Guide