As part of a migration, legacy non-ACI switches must be connected to the Cisco ACI fabric. All non- ACI switches run per-VLAN RSTP. After the non-ACI switches are connected to Cisco ACI, the STP conve

BPDU guard shuts down a port upon receiving a BPDU, which would prevent the external switch from establishing a connection if BPDUs are expected as part of STP operation.

Aggressive STP timers would likely exacerbate convergence issues and increase network instability in a scenario involving mismatched STP domains.

BPDU filtering prevents BPDUs from being sent or received on an interface, effectively disabling STP on that link and potentially leading to forwarding loops if the external network relies on STP for loop prevention.

Configuring 'STP type link shared' on the external non-ACI switch interfaces facing the ACI fabric is crucial because ACI itself does not run traditional STP. This setting allows the external switch to treat the ACI connection as a shared medium, effectively preventing STP microloops and CPU spikes during convergence by ensuring only one STP instance from the external network interacts with the fabric.