Juniper JUNOSE 11.1.X MULTICAST ROUTING, Configuration Manual

Page: 102 / 270

Overview
The IPv4 implementation of PIM supports PIM dense mode, PIM sparse mode, PIM
sparse-dense mode, and PIM source-specific multicast (PIM SSM).
Figure 8 on page 80 represents how PIM builds a source, group (S,G) entry in a
source-rooted tree (SRT). When multiple routers are connected to a multiaccess
network, one router becomes 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.
Figure 8: Source-Rooted Tree
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.
PIM Dense Mode
PIM dense mode uses a reverse-path multicast, flood-and-prune mechanism. The
protocol was developed for situations that meet one or more of the following criteria:
■
Sources and receivers are close together, and there are many more receivers
than sources.
■
There is a constant stream of multicast data.
■
There is a lot of multicast data.
Dense-mode routing protocols use SRT algorithms . An SRT algorithm establishes a
tree that connects each source in a multicast group to the members of the group. All
traffic for the multicast group passes along this tree.
80 ■
Overview
JUNOSe 11.1.x Multicast Routing Configuration Guide