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

 To enable communication between the subnets 192.168.1.0/24 and 172.18.1.0/24 using Cisco ACI fabric, it is necessary to configure the subnets appropriately. For option B, setting 172.18.1.0/24 as an External subnet for an external EPG under L3out_A allows it to be recognized as part of an external network, facilitating communication with other networks within the ACI environment. Similarly, for option D, configuring 172.18.1.0/24 with the Export Route Control scope under L3out_B ensures that this route is advertised out of L3out_B, allowing it to reach other network segments, including those connected via L3out_A where the subnet 192.168.1.0/24 resides. These configurations are crucial for proper routing between these two distinct subnets across the Cisco ACI fabric.

References := ( Implementing Cisco Application Centric Infrastructure Official Cert Guide )

 For a full mesh Cisco ACI Multi-Site architecture, configuring the BGP-EVPN Router-ID on each spine is essential. This configuration ensures unique identification and proper routing of traffic within the overlay network1