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



Apparently you forgot to use the -t nat table switch in the pre/post-routing instructions.

This is important because it specifies the packet matching table which the command should operate on.

This type of NATing needs all 3 components: PREROUTING - for altering packets as soon as they come in, OUTPUT - for altering locally-generated packets before routing and POSTROUTING - for altering packets as they are about to go out.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.