GRE over IPSec - tunnel mode

Hi there,

I successfully managed to establish a GRE over IPSec connection following this article: https://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD40312

I have a Fortigate 100E and a CISCO 2901 router as connection endpoints.

I wuold like to test a connection with transport-mode set to tunnel-mode, but when I set this mode on both devices I get an error and the link do not go up.

Can you help me please?

Very kind regards.

Alessio