Fortigate: ike Negotiate SA Error: ike ike [6633]

Site-to-Site IPSec VPN did not work suddenly.

diag debug application ike -l

diag debug enable

ike Negotiate SA Error: ike ike [6633]

It had the Phase 1 Proposal not match between the Two Fortinet Firewalls.

Before parts of the setting changed, the tunnel was working.

However, when changing done but not the Phase 1 Proposal, error occurred.

Required to set the Phase 1 Proposal also.

Then, the tunnel was back to normal.

Finally:

diag debug disable

Update