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JunosE 11.3.x Multicast Routing Configuration Guide
Reverse-Path Forwarding
144
An anycast address enables a device to send a datagram to one recipient out of a set
of recipients.
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 144 describes the function of each the protocol that the router supports.
Table 8: Function of Multicast Protocols on a Router
Protocol
Multicast Listener Discovery (MLD)
Protocol Independent Multicast Protocol (PIM)
BGP Multicast Protocol
The router supports up to 16,384 multicast forwarding entries (multicast routes) at any
time.
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.
Function
Discovers hosts that belong to multicast group.
Discovers other multicast routers that should
receive multicast packets.
Routes multicast datagrams between
autonomous systems.
Copyright © 2010, Juniper Networks, Inc.
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