R3303-HP HSR6800 Routers IP Multicast Configuration Guide

322
• The DR at the source side and the RP need to implement complicated encapsulation and
de-encapsulation of IPv6 multicast packets.
• IPv6 multicast packets are delivered along a path that might not be the shortest one.
• An increase in IPv6 multicast traffic heavily burdens the RP, increasing the risk of failure.
To solve these issues, IPv6 PIM-SM allows an RP or the receiver-side DR to initiate an SPT switchover
process as follows:
• The RP initiates an SPT switchover process:
When the RP receives the first IPv6 multicast packet, it sends an (S, G) join message toward the
IPv6 multicast source to establish an SPT between the DR at the source side and the RP. Subsequent
IPv6 multicast data travels along the established SPT to the RP.
For more information about switchover to SPT initiated by the RP, see "Multicast source
regi
stration."
• The receiver-side DR initiates an SPT switchover process:
a. When the receiver-side DR receives the first IPv6 multicast packet, it initiates an SPT switchover
process, as follows:
b. The receiver-side DR sends an (S, G) join message toward the IPv6 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, establishing an SPT branch.
c. When the IPv6 multicast packets travel to the router where the RPT and the SPT deviate, the
router drops the multicast packets that travel along the RPT and sends an RP-bit prune message
to the RP. After receiving this prune message, the RP sends a prune message toward the IPv6
multicast source (suppose only one receiver exists) to implement SPT switchover.
IPv6 multicast data is directly sent from the source to the receivers along the SPT.
IPv6 PIM-SM builds SPTs through SPT switchover more economically than IPv6 PIM-DM does through the
flood-and-prune mechanism.
Assert
IPv6 PIM-SM uses a similar assert mechanism as IPv6 PIM-DM does. For more information, see "Assert."
IPv6 BIDIR-PIM overview
In some many-to-many applications, such as multi-side video conference, there might be multiple
receivers interested in multiple IPv6 multicast sources simultaneously. With IPv6 PIM-DM or IPv6 PIM-SM,
each router along the SPT must create an (S, G) entry for each IPv6 multicast source, consuming a lot of
system resources. IPv6 BIDIR-PIM is introduced to address this problem. Derived from IPv6 PIM-SM, IPv6
BIDIR-PIM builds and maintains bidirectional RPTs, each of which is rooted at an RP and connects IPv6
multiple multicast sources with multiple receivers. Traffic from the IPv6 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.
IPv6 BIDIR-PIM is suitable for networks with dense multicast sources and dense receivers.
The working mechanism of IPv6 BIDIR-PIM is summarized as follows:
• Neighbor discovery
• RP discovery
• DF election
• Bidirectional RPT building