IPSEC site to site VPN Tunnel to external partner goes down irregularly / flaps
Hi
I have a Fortigate 91G and created an IPSEC site to site tunnel to a firewall of an external partner with preshared key (I think Cisco Firewall but info is not disclosed). The tunnel drops from time to time - there is no pattern why. It reconnects immediately but the session for users is lost and they need to turn off and on their LAN / VPN connection to be able to reconnect to the partner's systems. I checked the configuration multiple time and it's exactly the same as the partner uses (IKEv2, preshared key, Phase1: SHA256, AES256, Diffie-Hellman 14, Key-Lifetime 43200, Phase2 Lifetime: 3600s).
I tried turning on and off the Phase2 Auto-negotiate and Auto Key Keepalive options but the tunnel keeps going down. I can't really tell why it goes down because I don't see anything in the logs - maybe I am looking at the wrong place. I can tell that this is only happening during work time, the tunnel is stable outside of working hours.
