Where to add the Pre-Shared Key for the Server Authentication with Network Manager for L2TP/IPSEC?

Solution 1:

Are you comfortable with editing configuration files with a text editor? If so, I believe the answer of where to put the PSK is /etc/ipsec.secrets. You can try something like this:

: PSK "strongSwan" 

The file is documented in man ipsec.secrets or you can read about it here:

https://wiki.strongswan.org/projects/strongswan/wiki/IpsecSecrets

Let us know if that doesn't work for you.

Solution 2:

If you want a GUI solution, you can install an L2TP Network Manager plugin from ppa.

It can be done by

sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp
sudo apt-get update
sudo apt-get install network-manager-l2tp-gnome

It works with trusty and xenial, but the author did not build packages for vivid.

After you install the package you will be able to configure an L2TP connection in Network Manager

Update: Now the packages have been included in offiial Ubuntu repositories and PPA is not needed for Ubuntu 18.04+.