/ip pool
add name=VPN_Pool ranges=192.168.88.100-192.168.88.150
add name=OVPN_Pool ranges=192.168.88.32/30

/ip ipsec peer
add enc-algorithm=aes-128,aes-192,aes-256 exchange-mode=main-l2tp generate-policy=port-override lifetime=8h passive=yes secret=自訂密鑰 send-initial-contact=no
/ppp profile
set [find name=default-encryption] dns-server=192.168.88.1 local-address=192.168.88.1 remote-address=VPN_Pool
add name=OpenVPN dns-server=192.168.88.1 local-address=192.168.88.32 remote-address=OVPN_Pool use-encryption=yes change-tcp-mss=yes

/ppp secret
add name=帳號 password=密碼 profile=default

refer by http://www.mobile01.com/topicdetail.php?f=110&t=4038861