4000 Router Series IP Multicast Configuration Guide

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DR election

IPv6 PIM-SSM uses the same DR election mechanism as IPv6 PIM-SM. For more information, see "DR

election."

SPT building

The decision to build an RPT for IPv6 PIM-SM or an SPT for IPv6 PIM-SSM depends on whether the IPv6

multicast group that the receiver wants to join is included in the IPv6 SSM group range (FF3x::/32

reserved by IANA, where "x" represents any legal address scope).

Figure 51 SPT building in IPv6 PIM-SSM

As shown in Figure 51, Host B and Host C are receivers. They send MLDv2 report messages to their DRs

to express their interest in the multicast information that the IPv6 multicast source S sends to the IPv6

multicast group G.

After receiving a report message, the DR first checks whether the group address in the message is in the

IPv6 SSM group range and does the following:

• If the group address is in the IPv6 SSM group range, the DR sends a subscribe message hop by hop

toward the IPv6 multicast source S. All routers along the path from the DR to the IPv6 multicast

source create an (S, G) entry so as to build an SPT, which is rooted the IPv6 multicast source S and

has the receivers as its leaves. This SPT is the transmission channel in IPv6 PIM-SSM.

• If the group address is not in the IPv6 SSM group range, the receiver-side DR sends a (*, G) join

message to the RP, and the IPv6 multicast source registers with the source-side DR.

In IPv6 PIM-SSM, the term "channel" refers to an IPv6 multicast group, and the term "subscribe message"

refers to a join message.

IPv6 PIM support for VPNs

To support IPv6 PIM for VPNs, a multicast router that runs IPv6 PIM maintains an independent set of IPv6

PIM neighbor table, IPv6 multicast routing table, BSR information, and RP-set information for each VPN.

Source

Server

Host A

Host B

Host C

Receiver

IPv6 multicast packets

SPT

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