R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

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• Encapsulation and decapsulation are complex on the source-side DR and the RP.
• The path for an IPv6 multicast packet might not be the shortest one.
• The RP might be overloaded by IPv6 multicast traffic bursts.
To eliminate these weaknesses, IPv6 PIM-SM allows an RP or the receiver-side DR to initiate a switchover
to SPT:
• The RP initiates a switchover to SPT:
When the RP receives the first IPv6 (S, G) multicast packet, it sends an (S, G) source-specific join
message hop by hop toward the IPv6 multicast source. The routers along the path from the RP to
the IPv6 multicast source constitute an SPT branch. The subsequent IPv6 multicast data for the IPv6
multicast group can be forwarded to the RP along the branch without being encapsulated in
register messages.
For more information about the switchover to SPT initiated by the RP, see "IPv6 multicast source
regi
stration."
• The receiver-side DR initiates a switchover to SPT:
When the receiver-side DR receives the first IPv6 (S, G) multicast packet, it initiates a switchover to
SPT as follows:
a. The receiver-side DR sends an (S, G) source-specific join message hop by hop toward the IPv6
multicast source. The routers along the path from the RP to the source-side DR create an (S, G)
entry in their forwarding table to constitute an SPT branch.
b. When the multicast packets for the IPv6 multicast group are forwarded to the router where the
RPT and the SPT branches, the router drops the multicast packets that reach it along the RPT and
sends a prune message with the RP bit hop by hop to the RP. After receiving the prune message,
the RP forwards it toward the IPv6 multicast source (supposed only one receiver exists). Thus,
the switchover to SPT is completed.
c. Finally, the IPv6 multicast source sends the multicast packets for the IPv6 multicast group to the
receiver along the SPT.
With the switchover to SPT, IPv6 PIM-SM builds SPTs more economically than IPv6 PIM-DM does.
Assert
IPv6 PIM-SM uses a similar assert mechanism as IPv6 PIM-DM does. For more information, see "Assert."
IPv6 administrative scoping overview
Typically, an IPv6 PIM-SM domain contains only one BSR, which is responsible for advertising RP-set
information within the entire IPv6 PIM-SM domain. The information about all IPv6 multicast groups is
forwarded within the network that the BSR administers. This is called the "IPv6 non-scoped BSR
mechanism."
To implement refined management, you can divide an IPv6 PIM-SM domain into an IPv6 global-scoped
zone and multiple IPv6 administratively-scoped zones (admin-scoped zones). This is called the "IPv6
administrative scoping mechanism."