IGMPv3 enhancements

IGMPv3 is based on and is compatible with IGMPv1 and IGMPv2. It enhances the control capabilities of hosts and the query and report capabilities of IGMP devices.

Enhancements in control capability of hosts

IGMPv3 introduced two source filtering modes (Include and Exclude). These modes allow a host to receive or reject multicast data from the specified multicast sources. When a host joins a multicast group, one of the following occurs:

As shown in Figure 35, the network has two multicast sources: Source 1 (S1) and Source 2 (S2). Both of these sources can send multicast data to the multicast group G. Host B wants to receive the multicast data addressed to G from Source 1 but not from Source 2.

Figure 35: Flow paths of source-and-group-specific multicast traffic

In IGMPv1 or IGMPv2, Host B cannot select multicast sources when it joins the multicast group G. The multicast streams from both Source 1 and Source 2 flow to Host B whether or not it needs them.

In IGMPv3, Host B can explicitly express that it needs to receive multicast data destined to the multicast group G from Source 1 but not from Source 2.

Enhancements in query and report capabilities

IGMPv3 introduces IGMP group-and-source queries and IGMP reports carrying group records.