To achieve seamless IP addressing across sites, the bridge domain, subnet, and endpoint group (EPG) must be stretched. This allows endpoints in different sites to be in the same Layer 2 and IP subnet, enabling VM mobility and application continuity.
However, full Layer 2 broadcast flooding across sites is not recommended for scalability and network stability reasons. Therefore, Cisco ACI Multi-Site uses localized Layer 2 broadcast flooding, where broadcast, unknown unicast, and multicast (BUM) traffic is flooded only locally within each site, minimizing inter-site broadcast traffic and reducing risk of loops.
This combination supports maintaining Layer 2 adjacency and consistent IP addressing between sites with efficient broadcast handling.