According to theFortiSwitchOS 7.6 FortiLink Guideand theFortiSwitch 7.6 Study Guide, managed FortiSwitch units support a feature calledInter-VLAN Routing Offload. Traditionally, in a FortiLink deployment, traffic between VLANs is " hair-pinned " back to the FortiGate for routing and security inspection. However, to increase performance and reduce latency, the FortiGate can program the managed FortiSwitch to handle Layer 3 routing of trusted traffic locally.

The technical mechanism behind this performance gain is the use of theForwarding Information Base (FIB)programmed directly into the switch ' sASIC (Application-Specific Integrated Circuit). When routing offload is enabled (specifically using the set switch-controller-offload enable command on the VLAN interface), the FortiGate pushes the necessary routing table and gateway information to the switch hardware. This allows the FortiSwitch to perform packet lookups and forwarding decisions at wire speed within the silicon, bypassing the general-purpose CPU and the FortiLink control plane for that specific traffic flow.

The documentation notes that this feature requires anAdvanced Features Licenseon the tier-1 FortiSwitch and is typically applied to the switch closest to the FortiGate.2While dynamic routing (Option B) is supported on FortiSwitch, it is not theonlything offloaded; static routes and inter-VLAN gateway traffic are the primary use cases for this offload mechanism. Therefore, the correct architectural description is that the switch utilizes its hardware-based FIB to accelerate inter-VLAN communication.