Juniper JUNOSE 11.1.X MULTICAST ROUTING, Configuration Manual

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A multicast address enables a device to send a datagram to a specified set of
hosts, known as a multicast group, in different subnetworks.
IPv6 multicast improves network efficiency by allowing a host to transmit a datagram
to a targeted group of receivers. For example, a host may want to send a large video
clip to a group of selected recipients. It would be time-consuming for the host to
unicast the datagram to each recipient individually. If the host broadcasts the video
clip throughout the network, network resources are not available for other tasks. The
host uses only the resources it needs when multicasting the datagram.
Routers use multicast routing algorithms to determine the best route and transmit
multicast datagrams throughout the network. E Series routers support a number of
IPv6 multicast protocols on virtual routers (VRs). Each VR handles the interoperability
of IPv6 multicast protocols automatically. To start IPv6 multicast operation on a VR,
you access the context for that VR and configure the desired protocols on the selected
interfaces. Table 8 on page 148 describes the function of each the protocol that the
router supports.
Table 8: Function of Multicast Protocols on a Router
Function Protocol
Discovers hosts that belong to multicast group. Multicast Listener Discovery (MLD)
Discovers other multicast routers that should
receive multicast packets. Protocol Independent Multicast Protocol (PIM)
Routes multicast datagrams between
autonomous systems. BGP Multicast Protocol
The router supports up to 16,384 multicast forwarding entries (multicast routes) at
any time.
Reverse-Path Forwarding
IP multicasting uses reverse path forwarding (RPF) to verify that a router receives a
multicast packet on the correct incoming interface. The RPF algorithm enables a
router to accept a multicast datagram only on the interface from which the router
sends a unicast datagram to the source of the multicast datagram.
When the router receives a multicast datagram from a source for a group, the router
verifies that the packet was received on the correct RPF interface. If the packet was
not received on the correct interface, the router discards the packet. Only packets
received on the correct RPF interface are considered for forwarding to downstream
receivers.
When operating in sparse-mode, the routers perform an RPF lookup to identify the
upstream router from which to request the data and then send join messages for the
multicast stream only to that router.
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IPv6 Multicast Overview
JUNOSe 11.1.x Multicast Routing Configuration Guide