PDF 300-630 Study Guide

 To establish intra-VRF communication between two EPGs deployed across different sites with different bridge domains, stretching the bridge domain and EPG components is necessary. Option D, “bridge domain,” and Option E, “EPG,” must be configured as stretched to facilitate communication across different sites within the same VRF. References:= Implementing Cisco Application Centric Infrastructure Official Cert Guide

 In Cisco ACI fabric, STP BPDUs are flooded in the bridge domain VLAN. This allows the BPDUs to be propagated throughout the fabric, maintaining the STP topology2.

References := Implementing Cisco Application Centric Infrastructure Official Cert Guide

 For the ISN implementation between Cisco ACI data centers using Multi-Site, OSPF must be configured on subinterfaces for dynamic routing, and BIDIR-PIM must be set up on all ISN routers for efficient bidirectional multicast traffic routing. References := (Implementing Cisco Application Centric Infrastructure Official Cert Guide)

In a network-centric design within Cisco ACI, there is open communication between EPGs, and a bridge domain typically has one subnet and one EPG. This design is often used for initial migrations and is based on traditional networking concepts.

References := Network Centric to ACI Centric Migration - Cisco