3Com Switch 4800G 24-Port Configuration Manual page 616

616 C 46: IGMP C
HAPTER
Enhancements in
IGMPv3
n
ONFIGURATION
The support for the Exclude mode varies with device models.
Built upon and being compatible with IGMPv1 and IGMPv2, IGMPv3 provides
hosts with enhanced control capabilities and provides enhancements of query and
report messages.
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 a designated multicast source. When a host joins a
multicast group:
If it needs to receive multicast data from specific sources like S1, S2,
■
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,
■
report with the Filter-Mode denoted as "Exclude Sources (S1, S2,
As shown in Figure 185, 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 185 Flow paths of source-and-group-specific multicast traffic
Source 1
Source 2
Packets (S1,G)
Packets (S2,G)
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.
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Host A
Receiver
Host B
Host C
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