Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : Cluster virtual MAC addresses : Diagnosing packet loss with two FortiGate HA clusters in the same broadcast domain : Changing the HA group ID to avoid MAC address conflicts
  
Changing the HA group ID to avoid MAC address conflicts
Change the Group ID to change the virtual MAC address of all cluster interfaces. You can change the Group ID from the FortiGate CLI using the following command:
config system ha
set group-id <id_integer>
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