Bidir-Pim Overview - HP A8800 Configuration Manual

To solve the issues, PIM-SM allows an RP or the DR at the receiver side to initiate an SPT switchover
process:
1. The RP initiates an SPT switchover process
Upon receiving the first multicast packet, the RP sends an (S, G) join message hop by hop towards
the multicast source to establish an SPT between the DR at the source side and the RP. The
subsequent multicast data from the multicast source travels along the established SPT to the RP.
For more information about the SPT switchover initiated by the RP, see
registration."
2. The receiver-side DR initiates an SPT switchover process
Upon receiving the first multicast packet, the receiver-side DR initiates an SPT switchover process,
as follows:
The receiver-side DR sends an (S, G) join message hop by hop towards the multicast source.
When the join message reaches the source-side DR, all the routers on the path have installed the
(S, G) entry in their forwarding table, and thus an SPT branch is established.
When the multicast packets travel to the router where the RPT and the SPT deviate, the router
drops the multicast packets received from the RPT and sends an RP-bit prune message hop by
hop to the RP. Upon receiving this prune message, the RP sends a prune message towards the
multicast source (supposing that only one receiver exists). Thus, SPT switchover is completed.
Finally, multicast data is directly sent from the source to the receivers along the SPT.
PIM-SM builds SPTs through SPT switchover more economically than PIM-DM does through the "flood
and prune" mechanism.
Assert
PIM-SM uses a similar assert mechanism as PIM-DM does. For more information, see "Assert."

BIDIR-PIM overview

In some many-to-many applications, such as multi-side video conference, there may be multiple receivers
interested in multiple multicast sources simultaneously. With PIM-DM or PIM-SM, each router along the
SPT must create an (S, G) entry for each multicast source, consuming a lot of system resources. BIDIR-PIM
is introduced to address this problem. Derived from PIM-SM, BIDIR-PIM builds and maintains
bidirectional RPTs, each of which is rooted at an RP and connects multiple multicast sources with multiple
receivers. Traffic from the multicast sources is forwarded through the RP to the receivers along the
bidirectional RPT. In this case, each router needs to maintain only a (*, G) multicast routing entry, saving
system resources.
BIDIR-PIM is suitable for networks with dense multicast sources and dense receivers.
The operating mechanism of BIDIR-PIM is summarized as follows:
Neighbor discovery
•
RP discovery
•
DF election
•
• Bidirectional RPT building
Neighbor discovery
BIDIR-PIM uses the same neighbor discovery mechanism as PIM-SM does. For more information, see
"Neighbor discovery."
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"Multicast source