Huawei Quidway S3900 Series Operation Manual page 399

Operation Manual – Multicast Protocol
Quidway S3900 Series Ethernet Switches-Release 1510
All the receiver hosts participating in multicast transmission must support the IGMP
protocol. The hosts participating IP multicast transmission can join in or exit a multicast
group anywhere and anytime, without being restricted on the total number of group
members.
The multicast router need not and cannot save the membership information of all the
hosts. It just checks the network segment connected with each interface by IGMP to
see whether there are receivers of a multicast group, namely, group members. While
each host saves only the information that which multicast groups it joins.
I. Working mechanism of IGMPv1
VRP implements the IGMPv1 protocol according to RFC1112. IGMPv1 manages the
multicast groups based on the query/response mechanism. With the help of the Layer 3
routing protocol, IGMP selects the designated router (DR) as the querier, which is
responsible for sending query messages. Figure 6-1 describes the IGMPv1 message
interaction in the network:
Ethernet
query
Host A
query
report
Figure 6-1 Working mechanism of IGMPv1
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 the multicast group G1, Host B and Host C will
multicast IGMP host report packets (carrying the address of the multicast group
G1) to declare that they will join in the multicast group G1.
All the hosts and routers in the network receive the IGMP host report packets and
get to know the address of the multicast group G1. In this case, if other hosts in the
network want to join in the multicast group G1, they will not send IGMP host report
packets about G1. If some hosts in the network want to join in another multicast
DR
query
report
Assert
report
query
Host B
Huawei Technologies Proprietary
6-3
Chapter 6 IGMP Configuration
report
query
Host C