Chapter 1 What’s New for FortiOS 5.0 : New features in FortiOS 5.0 Patch 4 : Server load balancing enhancements : SNMP traps
  
SNMP traps
FortiGate units can now send SNMP traps when the FortiGate unit determines that one of the servers in a server load balance group has gone down. The OID for the trap is .fgTrapServerLoadBalanceRealServerDown.
You can use the following CLI command to enable this trap:
config system snmp community
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set events load-balance-real-server-down enable
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