Although the L2TP/IPsec VPN protocols were primarily developed by Microsoft and Cisco, there are open source alternatives that work well in Linux. L2TP/IPsec is an older VPN protocol but it is still quite popular despite the Snowden revelations that the NSA may have deliberately weakened the protocol. It supports various encryption ciphers and is built-in to Microsoft Windows and many routers.
If you want to use L2TP/IPsec on Linux you are probably going to need to install a few extra packages. I wrote this tutorial on Linux Mint 17.3 Cinnamon desktop edition, but it should be very similar for other flavors of Linux, and I will discuss these as well. Plenty of screenshots are included below.