Synchronizing TCP sessions
Synchronize TCP sessions so that if one FortiGate fails, the TCP sessions it was processing can continue to be processed by the remaining FortiGates. After the FortiGate fails, the router or load balancer re-distributes sessions to the FortiGates that are still running. The remaining FortiGates can continue to process these sessions because the sessions have been synchronized with the session tables of all the FortiGates in the deployment.
Enter the following commands on each FortiGate to synchronize TCP sessions with all FortiGates:
config system ha
set session-pickup enable