Configure VPN L2TP/IPSec on Ubuntu for Ubuntu Linux

1. sudo apt-get install network-manager-l2tp

2. sudo apt-get install network-manager-l2tp-gnome

3. Settings > Network > Click on "+" > Then choose "Layer 2 Tunneling Protocol (L2TP)"

4. Input VPN name into "Name" textbox.

5. Input host name into "Gateway" textbox.

6. Input user name into "Username" textbox. 

7. Input password into "Username" textbox. 

8. Choose "IPSec Settings".

9. Tick "Enable IPsec tunnel to L2TP host" checkbox

10. Input shared secret into "Pre-shared key". textbox

Bonus:

sudo service xl2tpd stop

sudo systemctl disable xl2tpd