Refer to the exhibits.

According to the FortiSwitchOS 7.6 Administration Guide and the FortiSwitch 7.6 Study Guide , the Loop Guard feature protects Layer 2 networks from switching loops and broadcast storms. Unlike standard STP loop protection mechanisms, FortiSwitch Loop Guard operates by periodically sending out proprietary Loop Guard Data Packets (LGDP) / probe frames out of ports where loop guard is enabled.

The loop-detection logic evaluates whether these probe frames return to the switch:

Frame Received Back on the Same Port (Option B): If a loop guard broadcast frame transmitted out of port1 traverses an external unmanaged hub, switch, or looped cable and is received back on port1, the switch detects a downstream loop directly connected to that port.

Frame Received on Another Port of the Same Switch (Option A): In multi-homed connections to a switched network (such as port1 and port2 sharing the same Layer 2 broadcast domains/VLANs), a loop guard frame sent from port1 that loops through the switched network and is received on port2 proves that an active Layer 2 loop exists between those two switch interfaces.

When a loop condition is verified by either scenario, FortiSwitch changes the status of the protected port to Triggered (as verified in the CLI output of the exhibit) and takes the port out of service to isolate the loop.

Regarding the incorrect options: Option C describes Spanning Tree loop guard behavior (loss of BPDUs on non-designated ports), not the FortiSwitch proprietary loop guard mechanism. Option D describes Storm Control or rate limiting, which acts on packet volume thresholds rather than loop-detection probe frames.