In a Cisco ACI Multi-Site fabric, the Inter-Site BUM Traffic Allow option is enabled in...

 In a Cisco ACI Multi-Site fabric, when the Inter-Site BUM Traffic Allow option is enabled for a stretched bridge domain, ingress replication on the spines in the source site is used to forward Broadcast, Unknown unicast, and Multicast (BUM) traffic to all endpoints in the same broadcast domain. This method ensures that BUM traffic is replicated and sent out through the spines to the destination sites.