Cisco Enterprise Network Core Technologies (ENCOR) Practice Exam

In IGMPv3 (Internet Group Management Protocol version 3), the functionality that allows hosts to specify included or excluded sources is facilitated by the membership report message. This version of IGMP introduces the ability for hosts to express their interest in receiving multicast data only from specific sources, rather than receiving multicast traffic from all sources by default.

Through membership report messages, a host can send information indicating which source(s) it wants to receive traffic from (included sources) and which source(s) it does not wish to receive traffic from (excluded sources). This selective forwarding capability is particularly valuable in scenarios where multicast streams come from multiple sources, allowing for better control over the multicast traffic that is delivered to the receiver.

The other options do not provide this source filtering functionality; they serve different roles in the IGMP process. For example, the leave group message is used when a host wants to leave a multicast group, while the join group message indicates that a host wants to start receiving multicast data for a specific group. Neither of these messages provides functionality to control the source from which the data is received, hence making the membership report message the critical feature that supports source inclusion and exclusion in IGMPv3.