Enabling LLDP reception allows the FortiGate to receive and store LLDP messages, learn about active neighbors, and makes the LLDP information available.

LLDP can be activated globally:

config system global
  set lldp-reception enable
  set lldp-transmission enable
end

Or per interface:

config system interface
  edit <port>
    set lldp-reception enable
    set lldp-transmission enable
  next
end

The following commands do show the neighbors:

diagnose lldprx neighbor {summary | details | clear}

diagnose lldprx port {details | summary | neighbor | filter}

diagnose lldprx port neighbor {summary | details}

Note that the port index in the output corresponds to the port index from the following command:

diagnose netlink interface list port2 port3 | grep index