H3C Technologies H3C S7500E Series Switches - Manual (Page 112)

5-5
Figure 5-2 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.
z TO_IN: The filtering mode has changed from Exclude to Include.
z TO_EX: The filtering mode has changed from Include to Exclude.
z ALLOW: The Source Address fields in this Group Record contain a list of the additional
sources that the system wishes to hear from, for packets sent to the specified multicast
address. If the change was to an Include source list, these are the addresses that were