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.
PIM Sparse Mode
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 81.
Copyright © 2010, Juniper Networks, Inc.80
JunosE 11.2.x Multicast Routing Configuration Guide
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