H3C S3610-28P Operation Manual page 749

Operation Manual – Multicast Protocol
H3C S3610&S5510 Series Ethernet Switches
5.1.2 Work Mechanism of 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 a multicast routing protocol (such as
PIM) serves as the IGMP querier.
Note:
For more information about DR, refer to
Figure 5-1 Joining multicast groups
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
follows:
1) The IGMP querier (Router B in the figure) periodically multicasts IGMP queries
(with the destination address of 224.0.0.1) to all hosts and routers on the local
subnet.
Figure 5-1. The basic process that the hosts join the multicast groups is as
DR election.
5-2
Chapter 5 IGMP Configuration