Multicast Routing Protocols - HP 7102dl - ProCurve Secure Router Configuration Manual

Configuring Multicast Support for a Stub Network
Overview
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Hosts send their IGMP reports to the multicast address rather then simply
to the multicast agent. When the other hosts in the group receive this
report, they cancel the report they would otherwise send out.
In this way, the multicast agent should receive one, and only one, report for
each multicast address for which a host group exists on a stub network.
When a host joins a group, it immediately sends a report in case it is the first
host in the group. Hosts send a leave message to their multicast agent when
they leave a group.
IGMP runs in version 1 and 2. The ProCurve Secure Router supports both.
Version 2 is the default.

Multicast Routing Protocols

A multicast routing protocol enables the router to determine every interface
through which it must forward traffic for a particular group. A router can use
IGMP to determine which directly connected networks need the traffic, but
generally it must run a multicast routing protocol to determine which directly
connected devices need the traffic. In other words, the multicast routing
protocol enables network devices to build trees over which traffic flows end-
to-end, from a source to all receivers.
Multicast routes are different from unicast routes because traffic destined to
a multicast address usually corresponds with many host addresses. Therefore
a router may need to copy a multicast packet and forward it out several
interfaces. Multicast routes also change relatively often as hosts join and leave
a group. In addition, multicast traffic often runs unidirectionally from a source
to receivers rather than bi-directionally as does unicast traffic. Multicast
routes can therefore by source-specific, and a router can use a multicast
routing protocol to determine through which interface traffic destined to a
particular group will arrive.
The ProCurve Secure Router supports Protocol-Independent Multicast-
Sparse Mode (PIM-SM), which relies on a the unidirectional flow of typical
multicast traffic. PIM-SM router uses IGMP to determine for which groups it
needs to receive multicast traffic. The router then joins a unique multicast tree
for each active multicast group. The tree is rooted at a rendezvous point (RP),
to which all sources must send multicasts for that group, and branches out
towards all hosts in the group. PIM-SM also lets routers generate a unidirec-
tional tree from an active source to all receivers.
The ProCurve Secure Router also supports IGMP proxy, which stub routers
can run in lieu of a multicast routing protocol. Like PIM-SM, IGMP proxy
allows a router to generate to receive and forward multicasts along a struc-