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 : Viewing MAC address conflicts on attached switches
  
Viewing MAC address conflicts on attached switches
If two HA clusters with the same virtual MAC address are connected to the same broadcast domain (L2 switch or hub), the MAC address will conflict and bounce between the two clusters. This example Cisco switch MAC address table shows the MAC address flapping between different interfaces (1/0/1 and 1/0/4).
1 0009.0f09.0002 DYNAMIC Gi1/0/1
1 0009.0f09.0002 DYNAMIC Gi1/0/4