This document discusses Cisco's Application Centric Infrastructure (ACI) and how to simulate an ACI environment. It defines ACI as Cisco's software-defined networking solution that uses an application-policy based model. It then describes the key components of ACI including Nexus switches, the Application Policy Infrastructure Controller (APIC), and ACI modes. It also explains that the Cisco ACI Simulator is a physical or virtual appliance that simulates an ACI environment. Finally, it provides instructions for accessing the ACI sandbox on the Cisco developer website to simulate an ACI environment without needing dedicated hardware.