Problem

Unable to connect to VPN using l2tp protocol on Linux.

Solution

1. Install latest version of network-manager-l2tp for Gnome and disable xl2tdp service.

sudo apt-get purge network-manager-l2tp network-manager-l2tp-gnome
sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp
sudo apt-get update
sudo apt-get install network-manager-l2tp network-manager-l2tp-gnome
sudo apt-get upgrade
sudo systemctl stop xl2tpd
sudo systemctl disable xl2tpd

2. Add these communication algorithms in settings of the VPN connection:

Phase1Algorithm: aes128-sha1-modp1024,3des-sha1-modp1024! Phase2Algorithm: aes128-sha1,3des-md5

3. On IPv4 tab uncheck Use this connection only for resources on this network

Sources

• https://askubuntu.com/questions/1072252/ubuntu-18-04-vpn-l2tp-with-psk/1188347#1188347
• https://github.com/nm-l2tp/NetworkManager-l2tp/wiki/Known-Issues