l2tp-client

Script for l2tp client, tested on Ubuntu (20.04) with shared secret only (AKA "ipsec preshared key").

install packages:

sudo apt-get install strongswan xl2tpd net-tools python3

"user", "password", "ipsec preshared key" and "vpn server ip address" are kept in config.ini

How to make a l2tp-vpn connection:

sudo python3 connect.py

Example:

$ sudo python3 connect.py
starting service...
ipsec up......
ipsec up established successfully
try to login with user and password
waiting 3s for checking in...
ppp established
ppp established, adding route...
P-t-P estabished
route add -net 10.0.0.0/8  gw 195.209.150.199

l2tp connected
finished

Alternative solutions:

https://hub.docker.com/r/ubergarm/l2tp-ipsec-vpn-client https://openthreat.ro/openwrt-l2tp-ipsec-vpn-client-for-mikrotik-server/

Server side manuals:

https://libreswan.org/wiki/VPN_server_for_remote_clients_using_IKEv1_with_L2TP https://interface31.ru/tech_it/2021/06/nastraivaem-l2tp-vpn-server-na-platforme-linux.html

Site-to-site manuals

https://adminotes.ru/vpn-l2tp-site-to-site-obedinenie-ofisov-cherez-vpn/