The N+1 High Availability (HA) architecture was introduced in FortiNAC-F version 7.6 to provide a more scalable and flexible redundancy model compared to the traditional 1+1 active/passive setup.
In an N+1 configuration, a single secondary (standby) appliance can provide coverage for multiple primary (active) Control and Application (CA) appliances.
To set up an N+1 HA cluster, there are two fundamental structural requirements:
A FortiNAC-F Manager (FortiNAC-M): Unlike standard 1+1 HA, which can be configured directly between two CAs, N+1 management is centralized. The FortiNAC-M acts as the orchestrator that manages the failover groups, monitors the health of the primaries, and coordinates the promotion of the secondary server if a primary fails.
A FortiNAC-F device designated as a Secondary: The cluster must have one appliance explicitly configured with the Secondary failover role. This device remains in a standby state, receiving database replications from all N primaries in its group until it is called upon to take over the functions of a failed unit

With a layer 3 isolation network type, FortiNAC-F supports multiple isolation networks of the same type, each with its own routed subnet. This design allows administrators to define more than one DHCP scope per isolation network type to accommodate multiple layer 3 isolation segments.

When FortiNAC-F manages VPN clients through a FortiGate, the agent plays a fundamental role in device identification that standard network protocols cannot provide on their own. In a standard VPN connection, the FortiGate establishes a Layer 3 tunnel and assigns a virtual IP address to the client. While the FortiGate sends a syslog message to FortiNAC-F containing the username and this assigned IP address, it typically does not provide the hardware (MAC) address of the remote endpoint's physical or virtual adapter.
FortiNAC-F relies on the MAC address as the primary unique identifier for all host records in its database. Without the MAC address, FortiNAC-F cannot correlate the incoming VPN session with an existing host record to apply specific policies or track the device's history. By running either a Persistent or Dissolvable Agent, the endpoint retrieves its own MAC address and communicates it directly to the FortiNAC-F service interface. This allows the "IP to MAC" mapping to occur.
Once FortiNAC-F has both the IP and the MAC, it can successfully identify the device, verify its status, and send the appropriate FSSO tags or group information back to the FortiGate to lift network restrictions.

MAC notification traps provide immediate notification when a MAC address is learned or removed on a port, resulting in faster and more accurate visibility updates compared to relying only on link state changes. They also allow FortiNAC-F to learn multiple hosts connected behind downstream unmanaged hubs or switches because each MAC address event is reported individually.