If IPv6 is enable in a Windows computer, the Line desktop application will not able to receive some pictures, videos and files.
Disable IPv6 may solve this problem.
Possible reason is the DNS requeset for Line is answered with AAAA recoreds, but the answered IPv6 addresss cannot be reached.
The most important part is the ipsec profile, ecp256 is required for Windows. Also, the L2TP secret is not supported by iOS.
Following is the configuration script for ROS 7.7:
/ip pool
add name=l2tp_pool ranges=192.168.100.190-192.168.100.200
/ppp profile
add name=l2tp-profile local-address=l2tp_pool remote-address=l2tp_pool
/ppp secret
add name=sclai profile=l2tp-profile service=l2tp
/ip ipsec profile
set [ find default=yes ] dh-group=ecp256,modp1024 enc-algorithm=\
aes-256,aes-192,aes-128
/interface l2tp-server server
set authentication=mschap2 default-profile=l2tp-profile enabled=yes use-ipsec=\
yes
