This document discusses two modes for connecting a Cisco Firepower Threat Defense (FTD) appliance to the leaf switches in an ACI fabric. Mode 1 connects the FTD using an EPG over L2 configuration, while Mode 2 connects the FTD using an EPF over L2 or using L3 mode connecting to a single virtual routing domain. It also provides steps for configuring access policies in ACI, including creating VLAN pools, application endpoint groups, contracts, and verifying the interfaces.