Which version of IGMP allows a host to receive traffic only from a specific source within a multicast group?

IGMP version 3 is the correct choice because it introduces support for source-specific multicast (SSM). This allows hosts to specify which sources they want to receive multicast traffic from within a given multicast group. In a network where multiple sources might transmit to the same multicast group, this capability helps to reduce unnecessary traffic and provides finer control for the receiving hosts.

By using IGMP v3, a host can include source filters in its membership reports, enabling it to join a multicast group while still controlling from which source(s) it will accept multicast traffic. This is particularly useful in scenarios where hosts are only interested in data from specific sources and want to avoid processing data from others.

In contrast, earlier versions like IGMP v1 and IGMP v2 do not have this functionality. They allow hosts to join a multicast group but provide no mechanism for filtering based on the source of the multicast traffic. Therefore, while these versions are effective for simpler multicast applications, they lack the granularity provided by IGMP v3.