Based on the FortiGate Infrastructure 7.6 study guide and the Hardware Acceleration technical documentation, the diagnose vpn tunnel list command provides the status of IPsec tunnel offloading to the Network Processor (NPU).
In the provided exhibit, the specific value npu_flag=20 (which corresponds to 0x20 in hexadecimal) indicates that the IPsec Security Association (SA) cannot be offloaded to the NPU. While the NPU may have visibility of the gateway IPs (npu_rgwy and npu_lgwy), the flag itself serves as a diagnostic indicator that the traffic must be processed by the system CPU rather than the hardware accelerator.
This lack of offloading typically occurs when the tunnel configuration uses a cipher (encryption algorithm) or an HMAC (authentication algorithm) that is not supported by the specific NPU model installed in the FortiGate. For example, if a tunnel is configured with a legacy or highly complex algorithm that the NP6 or NP7 chip is not designed to process in hardware, the FortiOS kernel handles the encryption and decryption, resulting in the npu_flag=20 status. Therefore, despite the presence of NPU-related fields, the specific flag value confirms that hardware acceleration is not active for these SAs.