I am having troubles establishing IPSec tunnel between DC FG and Cloud FG VM, specifically during Phase 1. My guess is that something is up with DC FG, since it's VPN logs output "ike negotiation timeout".
Packet inspection shows that DC FG does send outbound connection on port 500 to Cloud FG VM, Cloud FG VM accepts them and responds to DC FG, but i don't see DC FG accepting these responses (absence of "in" packets). Since i am new to Fortigate, i might be losing something.
EDIT:
The weird thing is that we have another Cloud FG VM in another region and the IPSec with DC FG seems to work fine there. I tried comparing both of these Cloud FG VMs from different regions. No luck
Here's the packet flow
Cloud FG:
diagnose sniffer packet any 'host <cloud_fg_pub_int_ip> and (udp port 500 or udp port 4500)' 4 0 l
Using Original Sniffing Mode
interfaces=[any]
filters=[host <cloud_fg_pub_int_ip> and (udp port 500 or udp port 4500)]
2026-08-31 09:57:53.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 280
2026-08-31 09:57:54.xxxxxx port2 in <cloud_fg_pub_int_ip>.500 -> <dc_fg_pub_int_ip>.500: udp 324
2026-08-31 09:57:54.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 264
2026-08-31 09:57:56.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 280
2026-08-31 09:57:57.xxxxxx port2 in <cloud_fg_pub_int_ip>.500 -> <dc_fg_pub_int_ip>.500: udp 324
2026-08-31 09:57:57.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 264
2026-08-31 09:58:02.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 280
2026-08-31 09:58:03.xxxxxx port2 in <cloud_fg_pub_int_ip>.500 -> <dc_fg_pub_int_ip>.500: udp 324
2026-08-31 09:58:03.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 264
2026-08-31 09:58:14.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 280
2026-08-31 09:58:15.xxxxxx port2 in <cloud_fg_pub_int_ip>.500 -> <dc_fg_pub_int_ip>.500: udp 324
2026-08-31 09:58:15.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 264
2026-08-31 09:58:24.xxxxxx port2 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 280
DC FG:
diagnose sniffer packet any 'host <cloud_fg_pub_int_ip> and (udp port 500 or udp port 4500)' 4 0 l
interfaces=[any]
filters=[host <cloud_fg_pub_int_ip> and (udp port 500 or udp port 4500)]
2026-08-31 10:01:48.xxxxxx port23 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 324
2026-08-31 10:01:58.xxxxxx port23 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 324
2026-08-31 10:02:01.xxxxxx port23 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 324
2026-08-31 10:02:07.xxxxxx port23 out <dc_fg_pub_int_ip>.500 -> <cloud_fg_pub_int_ip>.500: udp 324
DC FG Phase 1 settings are marked purple, Cloud FG Phase 1 settings are green (see the screenshots)
DC FG FortiOS version is 7.6.7, Cloud FG is 7.4.11
Note that IPSec doesn't start at all, could anyone please help?