Multicast Routing Protocols; Igmp - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IGMP

IGMP helps a router to determine which host groups have members in which
networks so that the router can properly forward multicast messages. Some
multicast routing protocols (including the protocol supported on the
ProCurve Secure Router) suppress multicasts unless a router or network
specifically requests them. IGMP also enables a router to determine the groups
for which it needs to request traffic.
Figures 10-3 and 10-4 illustrate how IGMP contains packets by allowing
routers to only forward multicast messages into networks that need them.
Group 99
Figure 10-3. Multicasting Without IGMP
An IGMP multicast agent, which is also called a querier, sends queries to
determine which host groups exist in the stub networks to which it directly
connects. The ProCurve Secure Router can act as an IGMP multicast agent.
Each subnet should have only one multicast agent to minimize overhead.
(Devices automatically defer a router to act as the agent and, if a network
includes more than one router, to the router with the lowest IP address.)
Configuring Multicast Support for a Stub Network
Multicast
packet
Switch
Multicast
packet
Router
Multicast
packet
Switch
Overview
10-5