Chapter 9 High Availability for FortiOS 5.0 : FortiGate Session Life Support Protocol (FGSP) : Synchronizing UDP and ICMP (connectionless) sessions
  
Synchronizing UDP and ICMP (connectionless) sessions
In many configurations, due to their non-stateful nature, UDP and ICMP sessions don't need to be synchronized to naturally failover. However, if its required you can configure the FGSP to synchronize UDP and ICMP sessions by entering the following command:
config system ha
set session-pickup enable
set session-pickup-connectionless enable
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