Igmp Proxy - HP 7102dl - ProCurve Secure Router Configuration Manual

Configuring Multicast Support for a Stub Network
Overview
tured, unidirectional path. However, a router running IGMP proxy cannot
establish different routes for different multicast groups. It must receive all
multicasts on the same incoming, or upstream, interface. In addition, a router
running IGMP proxy cannot transit multicast traffic. The router can forward
the multicasts through various outgoing, or downstream, interfaces depend-
ing on the memberships for that group in the connecting networks.
Because PIM-SM enables more functions than IGMP proxy and is often as
simple to configure, it is usually recommended that you configure your router
to use PIM-SM rather than IGMP proxy for multicast support. See Chapter 11:
Configuring Multicast Support with PIM-SM.

IGMP Proxy

IGMP proxy allows a stub router to act as a multicast host on behalf of
connected clients to a remote multicast source or to a remote router running
a multicast routing protocol. The stub router receives multicasts from the
source just as a typical host would. The stub router can then forward this
traffic out the necessary interfaces.
Only stub routers should use IGMP proxy for multicast support. A stub router
serves as a gateway to a stub network—that is, a network that originates and
terminates, but does not transit, traffic. Because the router will only receive
multicasts on one interface, the router does not need to determine where to
send joins for a particular group. It can simply forward all IGMP reports to the
default helper address. This address is the address of the multicast source or
any of device that runs a multicast routing protocol and receives traffic from
the source.
The stub router uses IGMP alone to determine outgoing interfaces for multi-
cast traffic. Because it is a stub router, it does not need to receive the PIM-SM
joins that would allow it to pass multicast traffic to other routers in a
multicast tree.
IGMP proxy organizes a router's interfaces into upstream and downstream
interfaces, providing an ordered flow for multicast messages.
A router connects to stub networks through downstream interfaces. The
downstream interfaces run IGMP, sending queries to and receiving report, join,
and leave messages from multicast hosts.
A router connects to remote multicast sources through an upstream interface.
When downstream interfaces receive IGMP messages, the upstream interface
copies them, inserts its own address as the messages' source address, and
forwards the messages to the helper address. The multicast router or source
12-9