In most networks, that's enough for the switches to update their MAC forwarding tables with the new information.
However, some high-end switches might not clear their MAC tables correctly after a failover. So, they keep sending packets to the former primary even after receiving the gratuitous ARPs. In these cases, you should use the command shown on this slide to force the former primary to shut down all its interfaces for one second when the failover happens, excluding heartbeat and reserved management interfaces. This simulates a link failure that clears the related entries from the MAC table of the switches.

This design uses a FortiLink connection from FortiGate to managed FortiSwitch devices, so the connection is a FortiLink interface. Fortinet's FortiLink documentation states that on the FortiGate side, the FortiLink interface is configured as a physical or aggregate interface, and MCLAG peer connections use an 802.3ad aggregate interface to connect to both peer switches.
STP or RSTP is not the requirement here, because Fortinet documents that STP is not supported between a FortiGate and a FortiSwitch in FortiLink mode.

Encapsulation (such as IPsec, VXLAN, or FGSP synchronization) adds overhead to standard packets, often causing them to exceed the standard MTU of 1500 bytes and leading to fragmentation or dropped packets.
The Enterprise Firewall curriculum notes that while " jumbo packets " can be detected as possible attacks by IPS, adjusting MTU and MSS values to account for encapsulation should ideally be performed in a controlled environment . This allows administrators to accurately measure the required overhead and verify that the adjustments do not cause unintended network instability or performance degradation across the entire infrastructure.

This IPsec Phase 1 configuration defines a dynamic VPN tunnel that can accept connections from multiple peers. The settings chosen here suggest a configuration optimized for networks with intermittent traffic patterns while ensuring resources are used efficiently.
Key configurations and their impact:
set type dynamic - This allows multiple peers to establish connections dynamically without needing predefined IP addresses.
set ike-version 2 - Uses IKEv2, which is more efficient and supports features like EAP authentication and reduced rekeying overhead.
set dpd on-idle - Dead Peer Detection (DPD) is triggered only when the tunnel is idle, reducing unnecessary keep-alive packets and improving resource utilization. set add-route enable FortiGate automatically adds the route to the routing table when the tunnel is established, ensuring connectivity when needed. set proposal aes128-sha256 aes256-sha256 Uses strong encryption and hashing algorithms, ensuring a secure connection.
set keylife 28800 Sets a longer key lifetime (8 hours), reducing the frequency of rekeying, which is beneficial for stable connections.
Because DPD is set to on-idle, the tunnel will not constantly send keep-alive messages but will still ensure connectivity when traffic is detected. This makes the configuration ideal for networks with regular but non-continuous traffic, balancing security and resource efficiency.