H3C S7500 Series Operation Manual page 464

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
I. Working mechanism of IGMPv1
Comware implements the IGMPv1 protocol according to RFC1112. IGMPv1 manages
the multicast groups based on the query/response mechanism. With the help of Layer 3
routing protocols, IGMP selects the designated router (DR) as the querier responsible
for sending query messages.
the network:
Router A
Ethernet
Host A
(G2)
Figure 6-1 Working mechanism of IGMPv
A host joins in the multicast group in the following procedure:
The IGMP querier (such as DR) periodically multicasts IGMP general group query
messages to all the hosts in the shared network segment whose address is
224.0.0.1.
All hosts in the network receive the query messages. If some hosts (such as Host
B and Host C) are interested in multicast group G1, Host B and Host C will
multicast IGMP report messages (carrying the address of multicast group G1) to
declare that they will join in multicast group G1.
All the hosts and routers in the network receive the IGMP report messages and get
to know the address of multicast group G1. In this case, if other hosts in the
network want to join in multicast group G1, they will not send IGMP report
messages about G1. If some hosts in the network want to join in another multicast
group G2, they will send IGMP report messages about G2 to respond to the query
messages.
After the query/response process, the IGMP routers get to know that receivers of
multicast group G1 exist in the network, and generate the (*, G1) multicast
forwarding entries, according to which multicast data is forwarded.
Figure 6-1
Host B
(G1)
Query
Report
describes the IGMPv1 message interaction in
DR
Router B
Host C
(G1)
1
6-3
Chapter 6 IGMP Configuration