The FortiGate's DHCP server, configured on the FortiLink interface, uses the Vendor Class Identifier (VCI) string to identify connecting FortiSwitch devices. The exhibit shows the VCI string is explicitly set to FortiSwitch-SoC. This configuration restricts the DHCP server to only respond to DHCP requests from FortiSwitch System-on-a-Chip (SoC) models. If the new FortiSwitch being connected is not an SoC model, its VCI string (which contains its model name) will not match. As a result, the FortiGate will not assign it an IP address, the CAPWAP management tunnel cannot be established, and the FortiSwitch will remain offline.

A. The ip-managed-by-fortiipam setting is an optional feature for integrating with FortiIPAM and is not a mandatory requirement for basic FortiLink discovery and management.

B. The question states that the cabling has been verified as correct, making it less likely that the interface member is the primary issue, especially when a specific configuration error is shown.

C. A FortiLink interface can be of type aggregate to provide link redundancy using LACP. It is a valid configuration and is not required to be a single physical interface.

1. FortiOS 7.6.0 Administration Guide: In the "FortiLink" section, under "Configuring the FortiLink interface," the guide discusses DHCP settings. It explains that the dhcp-server-vci-string can be used to restrict which FortiSwitch models can connect. "When you add one or more VCI strings, the DHCP server responds only to a FortiSwitch with a matching VCI string." This confirms that a mismatch will prevent connection. (See section: Networking > FortiLink > Configuring the FortiLink interface).

2. FortiSwitch Managed by FortiOS 7.6 Study Guide: The "FortiLink mode" chapter describes the discovery process. It details that a factory-default FortiSwitch sends DHCP discover messages containing its model name in the VCI string (DHCP option 60) to find a managing FortiGate. This process fails if the FortiGate's DHCP server is configured to only accept a different, non-matching VCI string. (See chapter: FortiLink mode > FortiLink discovery).