Which policy is typically required for communication between two EPGs within an ACI fabric?

Cisco ACI uses contracts to define communication policies between EPGs, specifying what services an EPG can provide (provider) and what services another EPG can consume (consumer). This policy-driven approach enforces security and access control between different application tiers or tenants within the ACI fabric.

A VRF (Virtual Routing and Forwarding) instance provides tenant isolation at Layer 3 by maintaining separate routing tables, but it does not define inter-EPG communication policies directly.

A bridge domain is a Layer 2 forwarding construct in ACI that defines a broadcast domain and typically associates with one or more EPGs, but it does not regulate communication between EPGs.

A VLAN (Virtual Local Area Network) is a traditional Layer 2 segmentation technology, and while EPGs can be mapped to VLANs for external connectivity, VLANs themselves are not the policy mechanism for inter-EPG communication within the ACI fabric.