H3C Technologies H3C S12500 Series Switches - Manual (Page 100)

84
Enhancements in control capability of hosts
IGMPv3 has introduced source filtering modes (Include and Exclude), so that a host not only can join a
designated multicast group, but also can specify to receive or reject multicast data from designated
multicast sources. When a host joins a multicast group, one of the following situations occurs:
• If it needs to receive multicast data from specific sources like S1, S2, …, it sends a report with the
Filter-Mode denoted as "Include Sources (S1, S2, …)."
• If it needs to reject multicast data from specific sources like S1, S2, …, it sends a report with the
Filter-Mode denoted as "Exclude Sources (S1, S2, …)."
As shown in Figure 31 , the network comprises two multicast sources, Source 1 (S1) and Source 2 (S2),
both of which can send multicast data to multicast group G. Host B is interested only in the multicast data
that Source 1 sends to G but not in the data from Source 2.
Figure 31 Flow paths of source-and-group-specific multicast traffic
In the case of IGMPv1 or IGMPv2, Host B cannot select multicast sources when it joins multicast group G.
Therefore, multicast streams from both Source 1 and Source 2 will flow to Host B whether it needs them
or not.
When IGMPv3 is running between the hosts and routers, Host B can explicitly express that it needs to
receive the multicast data that Source 1 sends to multicast group G—denoted as (S1, G), rather than the
multicast data that Source 2 sends to multicast group G—denoted as (S2, G). Thus, only multicast data
from Source 1 will be delivered to Host B.
Enhancements in query and report capabilities
1. Query message carrying the source addresses
Compatible with IGMPv1 and IGMPv2, IGMPv3 supports general queries and group-specific
queries. In addition, it introduces group-and-source-specific queries.
{
A general query does not carry a group address, or a source address.
{
A group-specific query carries a group address, but no source address.
{
A group-and-source-specific query carries a group address and one or more source addresses.
2. Reports containing multiple group records
Unlike an IGMPv1 or IGMPv2 report message, an IGMPv3 report message is destined to
224.0.0.22 and contains one or more group records. Each group record contains a multicast
group address and a multicast source address list.