IPSec VPN between Linux and Windows 2012

I had to connect a Windows 2012 machine machine behind NAT to a CentOS 7 ipsec gateway with libreswan. No l2tp, just plain IPSec.
The windows machine itself was not a gateway, it was connected “alone”. So in my case there was no need for using RRAS.
I found it difficult to find
→ Read More: IPSec VPN between Linux and Windows 2012