1. install package
sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp
sudo apt-get update
sudo apt-get install network-manager-l2tp
sudo apt-get install network-manager-l2tp-gnome # gui case
2. stop xl2tpd service
sudo service xl2tpd stop
sudo update-rc.d xl2tpd disable
3. VPN Client setting
개인에게 부여된 vpn 계정으로 세팅
https://armagankaratosun.github.io/post/2018-09-02-setup-l2tp-vpn-on-ubuntu/