Which feature allows firewall ACLs to be configured automatically when new endpoints are attached to EPG?

ARP Gleaning is a mechanism for learning endpoint MAC and IP addresses by passively monitoring ARP traffic, not for automatically configuring firewall ACLs.

Network-stitching is a general term that might refer to connecting networks, but it's not a specific ACI feature for automated ACL configuration based on endpoint attachment.

Hardware Proxy in ACI refers to the function of spine switches in handling unknown unicast, broadcast, and multicast traffic, and is not directly related to dynamic ACL configuration for new endpoints.

Dynamic endpoint attach (or dynamic endpoint learning) in Cisco ACI is a core feature where the ACI fabric automatically detects when a new endpoint (such as a VM or bare-metal server) connects to an Endpoint Group (EPG). Upon detection, ACI automatically applies the pre-defined network policies associated with that EPG, including security policies like firewall ACLs, without manual intervention. This automation ensures consistent policy application and reduces configuration errors as endpoints move or are added.