FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
This article describes how to resolve active-passive HA (High Availability) cluster formation issues on FortiGate-6000 when both units are configured with the same chassis ID.
Scope
FortiGate-6000
Solution
Chassis IDs allow the FortiGate Clustering Protocol (FGCP) to identify each chassis. The chassis ID does not influence which unit becomes primary in the cluster.
If both FortiGate-6000s in an active-passive cluster are configured with the same chassis ID, the following error appears in the logs:
diagnose sys ha history read
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<2025-09-22 05:42:01> vcluster-1: F6KF30T0199000XX is selected as the primary because it's the only member in
the cluster.
<2025-09-22 05:41:42> F6KF30T0199000XX failed to join because of chassis-id conflict 1.
---clipped---
When this occurs, both FortiGate-6000s begin operating in HA primary mode without forming a cluster.
To resolve this issue:
Log in to one of the FortiGate-6000.
Change the chassis ID to a unique value (for example, 2):
config system ha
set chassis-id 2
end
Ensure that each FortiGate-6000 in the cluster has a different chassis ID (1 and 2).
