Internet Protocol Version; Reverse-Path Forwarding; Table 3: Function Of Multicast Protocols On A Router - Juniper JUNOSE 11.0.X MULTICAST ROUTING Configuration Manual

JUNOSe 11.0.x Multicast Routing Configuration Guide
Multicast IP packets contain a class D address in the Destination Address fields of
their headers. A class D address is the IP address of a multicast group. See
"Configuring IGMP" on page 43 and JUNOSe IP, IPv6, and IGP Configuration Guide,
for information about class D addresses.
IP multicast improves network efficiency by enabling a host to transmit a datagram
to a targeted group of receivers. For example, for a host to send a large video clip to
a group of selected recipients would be time-consuming 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
IP multicast protocols on virtual routers (VRs). Each VR handles the interoperability
of IP multicast protocols automatically. To start multicast operation on a VR, you
access the context for that VR and configure the desired protocols on the selected
interfaces. Table 3 on page 4 describes the function of each protocol that the router
supports.

Table 3: Function of Multicast Protocols on a Router

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.
4
IPv4 Multicast Overview
A broadcast address enables a device to send a datagram to all hosts on a
subnetwork.
A multicast address enables a device to send a datagram to a specified set of
hosts, known as a multicast group, in different subnetworks.
Protocol
Internet Group Membership Protocol (IGMP)
Protocol Independent Multicast Protocol (PIM)
Distance Vector Multicast Routing Protocol
(DVMRP)
BGP Multicasting Protocol
Function
Discovers hosts that belong to multicast group.
Discovers other multicast routers to receive
multicast packets.
Routes multicast datagrams within autonomous
systems.
Routes multicast datagrams between
autonomous systems.