Pim Sparse Mode; Joining Groups; Figure 21: Source-Rooted Tree - Juniper JUNOSE 11.0.X MULTICAST ROUTING Configuration Manual

JUNOSe 11.0.x Multicast Routing Configuration Guide
SSM is an extension to the Any Source Multicast (ASM) service model and facilitates
the deployment of broadcast (one-to-many) applications, such as Internet TV and
radio where large receiver audiences require traffic from a few well-known sources.
Figure 21 on page 216 represents how PIM builds an (S,G) entry in an SRT. When
multiple routers are connected to a multiaccess network, one router is assigned the
role of the designated router. The designated router receives data from the source
on interface 1/0 and multicasts the data to its downstream neighbors on interfaces
1/1, 2/0, and 2/1. In the designated router routing table, the entry for this operation
lists the source as the IP address of the source and the group as the IP address of the
multicast group.
Neighbors exchange hello messages periodically to determine the designated router.
The router with the highest network layer address becomes the designated router.
If the designated router subsequently receives a hello message from a neighbor with
a higher network layer address, that neighbor becomes the designated router.

Figure 21: Source-Rooted Tree

PIM Sparse Mode

In addition to the features PIM sparse mode supports for IPv4, this IPv6
implementation of PIM sparse mode also supports remote neighbors.
For a description of PIM sparse mode, see "Configuring PIM for IPv4 Multicast" on
page 79.

Joining Groups

A host's designated router (DR) sends join messages to the RP when that host wants
to join a group. When a host wants to leave a group, it communicates with its
designated router through MLD. When the designated router no longer has any hosts
that belong to a particular group, it sends a prune message to the RP.
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Overview