H3C Technologies H3C S7500E Series Switches - Manual (Page 109)

5-2
For more information about the ASM and SSM models, see Multicast Overview of the IP
Multicast Configuration Guide.
Introduction to IGMPv1
IGMPv1 manages multicast group memberships mainly based on the query and response
mechanism.
Of multiple multicast routers on the same subnet, all the routers can hear IGMP membership
report messages (often referred to as reports) from hosts, but only one router is needed for
sending IGMP query messages (often referred to as queries). So, a querier election mechanism
is required to determine which router will act as the IGMP querier on the subnet.
In IGMPv1, the designated router (DR) elected by the working multicast routing protocol (such
as PIM) serves as the IGMP querier.
For more information about DR, refer to PIM Configuration in the IP Multicast Configuration
Guide.
Figure 5-1 IGMP queries and reports
Query
Report
DR
Host A
(G2)
Host B
(G1)
Host C
(G1)
Ethernet
Router A Router B
IP network
Assume that Host B and Host C are expected to receive multicast data addressed to multicast
group G1, while Host A is expected to receive multicast data addressed to G2, as shown in