In a Cisco ACI Multi-Site setup, the ISN (Inter-Site Network) connects different ACI sites. For efficient multicast traffic routing, BIDIR-PIM (Bidirectional Protocol Independent Multicast) is configured throughout the ISN, which is why option B is correct. Increasing the ISN MTU (Maximum Transmission Unit) to support the maximum MTU sent by endpoints is crucial to prevent packet fragmentation or loss, making option C correct.
Options A, D, and E are not typically required for an ACI Multi-Site setup. Direct connectivity between Spine switches and ISN routers, as mentioned in options A and D, is usually established through leaf switches.
Option E, enabling IGMPv3 on ISN routers, is more relevant for managing multicast subscriptions within a single site.
References: = Implementing Cisco Application Centric Infrastructure Official Cert Guide