3Com Switch 8800 Advanced Software V5 Configuration Guide

526 CHAPTER 40: IGMP CONFIGURATION
Enhancements in
IGMPv3
Enhancements in control capability of hosts
In addition to group-specific queries, 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 a
designated multicast source. When a host joins a multicast group:
■ 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 167, 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 167 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 its interest in the multicast data Source 1 sends to multicast group G,
rather than the multicast data Source 2 sends to multicast group G. Thus, only
multicast data from Source 1 will be delivered to Host B.
c
CAUTION: Currently, Switch 8800s do not support the Exclude filtering mode.
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.
■ A general query does not carry a group address, nor a source address;
■ A group-specific query carries a group address, but no source address;
Source 2
Receiver
Host
A
Host B
Host C
Packets (S1,G)
Packets (S2,G)
Source 1