Ip Multicast (Igmp); How Igmp Operates - HP J3245A Installation And Configuration Manual

IP Multicast (IGMP)

In a network where IP multicast traffic is transmitted for various multimedia
applications, you can use the switch to reduce unnecessary bandwidth usage
on a per-port basis by configuring IGMP.

How IGMP Operates

The Internet Group Management Protocol (IGMP) is an internal protocol of
the Internet Protocol (IP) suite. IP manages multicast traffic by using
switches, multicast routers, and hosts that support IGMP. (In Hewlett-Pack-
ard's implementation of IGMP, a multicast router is not necessary as long as
the switch is configured to support IGMP with the querier feature enabled.)
A set of hosts, routers, and/or switches that send or receive multicast data
streams to or from the same source(s) are termed a multicast group, and have
the same multicast group address. The multicast group running version 2 of
IGMP uses three fundamental types of messages to communicate:
Query: A message sent from the querier (multicast router or switch)
asking for a response from each host belonging to the multicast group. If
a multicast router supporting IGMP is not present, then the switch must
assume this function in order to elicit group membership information
from the hosts on the network.
Report: A message sent by a host to the querier to indicate that the host
wants to be or is a member of a given group indicated in the report
message.
Leave Group: A message sent by a host to the querier to indicate that the
host has ceased to be a member of a specific multicast group.
Thus, IGMP identifies members of a multicast group (within a subnet) and
allows IGMP-configured hosts (and routers) to join or leave multicast groups.
Role of the Switch. When IGMP is enabled on the switch, it examines the
IGMP packets it receives:
To learn which of its ports are linked to IGMP hosts and multicast routers/
queriers belonging to any multicast group
To become a querier if a multicast router/querier is not discovered on the
network
Advanced Concepts
IP Multicast (IGMP)
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