ACI switches do not actively participate in Spanning Tree Protocol (STP). ACI switches forward spanning tree Bridge Protocol Data Units (BPDUs) across EPGs on which they are received. The spanning tree links are peer-to-peer (P2P), which does not cause loops until ACI acts as a hub for BPDUs. To avoid loops on switches connected to ACI, you can share the spanning tree link. You can also create the spanning tree interface policy to change spanning tree protocol settings on ACI Fabric.
In a PowerEdge MX environment integrated with the Cisco ACI, the best practice is to use Ethernet - No Spanning Tree as the uplink type for the MX SmartFabric. This disables STP on MX SmartFabric uplinks.
When using the Legacy Ethernet uplink in a PowerEdge MX SmartFabric environment, disable STP on the MX I/O modules by running the spanning-tree disable
command globally on the IOM command-line interface on both switches before creating a Legacy Ethernet uplink.