Multicast Packet Forwarding; Platform Considerations; Chapter 1 Configuring Ipv4 Multicast - Juniper JUNOSE 11.0.X MULTICAST ROUTING Configuration Manual

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.
When operating in dense-mode, routers that have multiple paths to the source of
the multicast stream initially receive the same stream on more than one interface.
In this case, the routers perform an RPF lookup to identify multicast data streams
that are not arriving on the best path and send prune messages to terminate these
flows.
The RPF lookup need not always be towards the source of the multicast stream. The
lookup is done towards the source only when the router is using a source-rooted tree
to receive the multicast stream. If the router uses a shared tree instead, the RPF
lookup is toward a rendezvous point and not toward the source of the multicast
stream.

Multicast Packet Forwarding

Multicast packet forwarding is based on the source (S) of the multicast packet and
the destination multicast group address (G). For each (S,G) pair, the router accepts
multicast packets on an incoming interface (IIF), which satisfies the RPF check
(RPF-IIF). The router drops packets received on IIFs other than the RPF-IIF and notifies
the routing protocols that a packet was received on the wrong interface.
The router forwards packets received on the RPF-IIF to a list of outgoing interfaces
(OIFs). The list of OIFs is determined by the exchange of routing information and
local group membership information. The router maintains mappings of (S,G, IIF) to
{OIF1, OIF2...} in the multicast routing table.
You can enable two or more multicast protocols on an IIF. However, only one protocol
can forward packets on that IIF. The protocol that forwards packets on an IIF owns
that IIF. A multicast protocol that owns an IIF also owns the (S,G) entry in the multicast
routing table.

Platform Considerations

For information about modules that support IP multicasting on the ERX7xx models,
ERX14xx models, and the Juniper Networks ERX310 Broadband Services Router:
For information about modules that support IP multicasting on the Juniper Networks
E120 and E320 Broadband Services Routers:
See ERX Module Guide, Table 1, Module Combinations for detailed module
specifications.
See ERX Module Guide, Appendix A, Module Protocol Support for information about
the modules that support IP multicasting.
Chapter 1: Configuring IPv4 Multicast

Platform Considerations

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