IGMPv3 enhancements

IGMPv3 is based on and is compatible with IGMPv1 and IGMPv2. It provides hosts with enhanced control capabilities and provides enhancements of query and report messages.

Enhancements in control capability of hosts

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

As shown in Figure 21, the network has two multicast sources, Source 1 (S1) and Source 2 (S2). Both of them can send multicast data to the multicast group G. Host B is interested in the multicast data that Source 1 sends to G but not in the data from Source 2.

Figure 21: 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. Multicast streams from both Source 1 and Source 2 flow to Host B whether or not it needs them.

When IGMPv3 runs between the hosts and routers, Host B can explicitly express that it needs to receive the multicast data that Source 1 sends to the multicast group G (denoted as (S1, G)). It also can explicitly express that it does not want to receive the multicast data that Source 2 sends to multicast group G (denoted as (S2, G)). Finally, only multicast data from Source 1 is delivered to Host B.

Enhancements in query and report capabilities