Resolving HA cluster chassis ID conflicts
In a FortiGate-6000 or 7000 FGCP HA configuration, if both FortiGates in the cluster are incorrectly configured with the same chassis ID, the FortiGate with the lowest serial number will be shut down. The other FortiGate will continue to operate as a standalone FortiGate in HA mode.
You can resolve the chassis ID conflict by restarting the shut down FortiGate-6000 or 7000 and configuring the FortiGate-6000s or 7000s with different chassis IDs. You should prevent the devices from forming a cluster before you change the chassis IDs. For example, you could change the chassis ID of the operating device or revert it to standalone mode before re-starting the shut down FortiGate.
Once both FortiGates are operating in HA mode with different chassis IDs, they will negotiate to form a cluster, and if their chassis IDs are different the cluster will begin to operate normally.
Also, if you are setting up a cluster of FortiGate-6301Fs or 6501Fs, before you configure HA, consider using the