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JunosE 11.3.x Multicast Routing Configuration Guide
PIM Sparse Mode
82
Figure 10: Detecting Duplication
The upstream routers responsible for the duplication send assert messages to determine
which router becomes the forwarder. Downstream routers listen to the assert messages
to discover which router becomes the forwarder.
This implementation of PIM sparse mode supports the following features:
Rendezvous point (RP) routers
Designated routers and designated router election
Join/prune messages, hello messages, assert messages, and register messages
Switching from a shared tree to a shortest path tree (SPT)
(* ,*,RP) support for interoperation with dense-mode protocols
RPF checks of multicast entries when unicast routing configuration changes
Timers for tree maintenance
Border, null, Rendezvous Point Tree (RPT), SPT, and wildcard flags
PIM sparse mode resolves situations that meet one or more of the following criteria:
The multicast group contains few receivers.
Multicast traffic is infrequent.
Wide area networks (WANs) separate sources and receivers.
Sparse-mode routing protocols use shared trees. In a shared tree, sources forward
multicast datagrams to a directly connected router, the designated router. The designated
router encapsulates the datagram and unicasts it to an assigned RP router, which then
forwards the datagram to members of multicast groups. See Figure 11 on page 83.
Copyright © 2010, Juniper Networks, Inc.
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