I’m working on implementing VPN tunnel IPSec GRE from Natted Linux box with Ubuntu.
I have found a very useful article, related to IPSec-GRE tunnel behind NAT, made with Cisco routers. I have successfully tested and implemented a mock-up in line with this article, where trick is based on the use of Loopback interface for the GRE. https://blog.dest-unreach.be/2008/07/11/terminating-an-ipsec-gre-tunnel-behind-nat
Nevertheless I still am unable to do the same from my Linux machine.
Could you please have a look to the article and let me know if you think I can translate/adapt it to Linux, and what is your feeling about such solution?
Thank you for your help