Refer to the exhibit. An engineer is implementing a BPDU filter on external switch interfaces that face the Cisco ACI fabric to prevent excessive TCNs from impacting the fabric. Which configuration…

Cisco ACI's Multi-destination Tree Protocol (MCP) is the primary loop prevention mechanism within the ACI fabric itself and for its interaction with external networks when STP is not running on external interfaces (e.g., due to BPDU filter). When BPDU filters are applied on external switches, they stop sending BPDUs to ACI, requiring ACI to rely on MCP to detect and prevent loops for multi-destination traffic, ensuring fabric stability.

BPDU Guard is typically used to shut down ports that receive BPDUs, and it's not the primary loop prevention mechanism for the ACI fabric itself when external switches are filtering BPDUs.

Applying an MSTP instance on Cisco ACI is not the correct approach; ACI uses its own forwarding model (MCP for multi-destination traffic) rather than traditional STP/MSTP for fabric-internal loop prevention.

Enabling STP on downlinks is contrary to the ACI architecture, which does not run traditional STP on its leaf ports connecting to endpoints or external devices; it uses MCP for loop prevention where necessary.