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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 613
■ “IGMP Configuration Task List” on page 617
■ “IGMP Configuration Example” on page 624
■ “Troubleshooting IGMP” on page 626
n
The term “router” in this document refers to a router in a generic sense or a Layer
3 switch 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 can be directly used to implement 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.
n
For more information about DR, refer to “DR election” on page 633.
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