Bidir-Pim Overview - HP MSR2003 Configuration Manual

The subsequent multicast data is forwarded to the RP along the SPT without being encapsulated
into register messages.
For more information about the switchover to SPT initiated by the RP, see
registration."
The receiver-side DR initiates a switchover to SPT:
•
The receiver-side DR periodically checks the forwarding rate of the multicast packets that the
multicast source S sends to the multicast group G. If the forwarding rate exceeds the specified
threshold, the DR initiates a switchover to SPT as follows:
a. The receiver-side DR sends an (S, G) source-specific join message toward the multicast source.
The routers along the path create an (S, G) entry in their forwarding table to constitute an SPT
branch.
b. When the multicast packets reach the router where the RPT and the SPT branches, the router
drops the multicast packets that travel along the RPT. It then sends a prune message with the RP
bit toward the RP.
c. After receiving the prune message, the RP forwards it toward the multicast source (supposed
only one receiver exists). Thus, the switchover to SPT is completed. The subsequent multicast
packets travel along the SPT from the multicast source to the receiver hosts.
With the switchover to SPT, PIM-SM builds SPTs more economically than PIM-DM does.
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 a multi-side video conference, multiple receivers might be
interested in the multicast data from multiple multicast sources. 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 addresses the problem. Derived from PIM-SM, BIDIR-PIM builds and maintains a bidirectional
RPT, which is rooted at the RP and connects the multicast sources and the receivers. Along the
bidirectional RPT, the multicast sources send multicast data to the RP, and the RP forwards the data to the
receivers. Each router along the bidirectional RPT needs to maintain only one (*, G) entry, saving system
resources.
BIDIR-PIM is suitable for a network with dense multicast sources and receivers.
Neighbor discovery
BIDIR-PIM uses the same neighbor discovery mechanism as PIM-SM does. For more information, see
"Neighbor discovery."
RP discovery
BIDIR-PIM uses the same RP discovery mechanism as PIM-SM does. For more information, see
discovery." In BIDIR-PIM, an RPF interface is the interface toward an RP, and an RPF neighbor is the
address of the next hop to the RP.
In PIM-SM, an RP must be specified with a real IP address. In BIDIR-PIM, an RP can be specified with a
virtual IP address, which is called the "rendezvous point address (RPA)." The link corresponding to the
RPA's subnet is called the "rendezvous point link (RPL)." All interfaces connected to the RPL can act as the
RPs, and they back up one another.
86
"Multicast source
"RP