Operation Manual – Multicast
H3C S3600 Series Ethernet Switches-Release 1510 Chapter 6 IGMP Configuration
6-1
Chapter 6 IGMP Configuration
6.1 Overview
6.1.1 Introduction to IGMP
Internet group management protocol (IGMP) is responsible for the management of IP
multicast members. It is used to establish and maintain membership between IP hosts
and their directly connected neighboring routers.
However, the IGMP feature does not transmit or maintain the membership information
among multicast routers. This task is completed by multicast routing protocols. All the
hosts participating in multicast must support the IGMP feature.
IGMP is divided into two function parts:
z Host side: the hosts participating IP multicast can join or exit a multicast group
anywhere at anytime, without being restricted on the total number of group
members.
z Router side: through the IGMP protocol, a multicast router checks the network
segment connected to each interface to see whether there are receivers of a
multicast group, namely, group members.
A multicast router needs not and cannot save the membership information of all the
hosts, while a host has to save the information that which multicast groups that it joins.
IGMP is asymmetric between the host and the router. The host needs to respond to the
IGMP query packets of the multicast routers, that is, report packet responses as an
IGMP hosts. The multicast router sends IGMP general query packets periodically and
determines whether any host of a specified group joins its subnet based on the
received response packets. When the router receives IGMP leave packets, it will send
IGMPv2 group-specific query packets to find out whether the specified group still has
any member.
6.1.2 IGMP Version
Until now, IGMP has three versions: including IGMP Version 1 (defined by RFC1112),
IGMP Version 2 (defined by RFC2236), and IGMP Version 3.
6.1.3 Work Mechanism of IGMPv1
IGMPv1 manages multicast groups mainly based on the query and response
mechanism.
Of multiple multicast routers on the same subnet, only one router is needed for sending
IGMP queries because all the routers can receive IGMP reports from hosts. So, a
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