According to theFortiOS 7.6 Study Guideand theFortiSwitch 7.6 FortiLink Guide, the automatic discovery and subsequent management of a FortiSwitch by a FortiGate controller is primarily facilitated by theLink Layer Discovery Protocol (LLDP). LLDP is an industry-standard, layer-2 protocol that allows network devices to advertise their identities and capabilities to neighbors on the same physical link.
When a factory-default FortiSwitch is connected to a FortiGate port (specifically one configured as a FortiLink interface), the switch automatically sends outLLDP advertisements. These advertisements include specificOrganizationally Specific TLVs (Type-Length-Values)that identify the device as a FortiSwitch and provide its management MAC address and current state. The FortiGate " listens " for these LLDP frames; once it receives a frame from a compatible FortiSwitch, it automatically lists the switch in theManaged FortiSwitchinventory as a " discovered " device awaiting authorization.
WhileZero-touch deployment (Option A)describes the overall goal of deploying a switch without manual CLI configuration, it is the underlyingLLDPprotocol that provides the technical mechanism for the initial detection. Once the switch is discovered via LLDP and authorized, the FortiGate uses a DHCP server on the FortiLink interface to assign an IP address to the switch and establishes a secureCAPWAP(Control and Provisioning of Wireless Access Points) tunnel for management. TheFortiLink heartbeat (Option D)is a secondary mechanism usedafterthe connection is established to monitor the health and status of the link, rather than for the initial detection of the device.