H3C Technologies H3C S3600 Series Switches - Manual (Page 397)

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z If it does not expect 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 3-2 , 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 3-2 Flow paths of source-and-group-specific multicast traffic
Source 2
Receiver
Host A
Host B
Host C
Packets (S1,G)
Packets (S2,G)
Source 1
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 its interest in the
multicast data Source 1 sends to multicast group G (denoted as (S1, G)), rather than the multicast data
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
IGMPv3 supports not only general queries (feature of IGMPv1) and group-specific queries (feature of
IGMPv2), but also group-and-source-specific queries.
z A general query does not carry a group address, nor a source address;
z A group-specific query carries a group address, but no source address;
z 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.
Group record types include:
z IS_IN: The source filtering mode is Include, namely, the report sender requests the multicast data
from only the sources defined in the specified multicast source list.
z IS_EX: The source filtering mode is Exclude, namely, the report sender requests the multicast data
from any sources but those defined in the specified multicast source list.