3Com Switch 8800 Advanced Software V5 Configuration Guide

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IGMP CONFIGURATION
When configuring IGMP, go to the following sections for the information you are
interested in:
■ “IGMP Overview” on page 523
■ “Configuring IGMP” on page 527
■ “Configuring Basic Functions of IGMP” on page 528
■ “Configuring IGMP Performance Parameters” on page 530
■ “Displaying and Maintaining IGMP” on page 534
■ “IGMP Configuration Examples” on page 534
■ “Troubleshooting IGMP” on page 536
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The term "router" in this document refers to a router in a generic sense or a
Switch 8800 running IGMP.
IGMP Overview As a TCP/IP protocol responsible for IP multicast group member management, the
Internet Group Management Protocol (IGMP) is used by IP hosts to establish and
maintain their multicast group memberships to immediately neighboring multicast
routers.
IGMP Versions So far, there are three IGMP versions:
■ IGMPv1 (documented in RFC 1112)
■ IGMPv2 (documented in RFC 2236)
■ IGMPv3 (documented in RFC 3376)
All IGMP versions support the Any-Source Multicast (ASM) model. In addition,
IGMPv3 provides strong support to the Source-Specific Multicast (SSM) model.
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, which sends periodical IGMP queries.