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a BSR. The BSR acts as the administrative core of the IPv6 PIM-SM domain. An IPv6 PIM-SM domain can
have only one BSR, but can have multiple C-BSRs. If the BSR fails, a new BSR is automatically elected from
the C-BSRs to avoid service interruption.
NOTE:
• An RP can provide services for multiple IPv6 multicast groups, but an IPv6 multicast group only uses one
RP.
• A device can act as a C-RP and a C-BSR at the same time.
As shown in Figure 95, each C-RP periodically unicasts its advertisement messages (C-RP-Adv messages)
to the BSR. An advertisement message contains the address of the advertising C-RP and the IPv6 multicast
group range to which it is designated. The BSR collects these advertisement messages and organizes the
C-RP information into an RP-set, which is a database of mappings between IPv6 multicast groups and RPs.
The BSR then encapsulates the RP-set in the bootstrap messages (BSMs) and floods the bootstrap
messages to the entire IPv6 PIM-SM domain.
Figure 95 BSR and C-RPs
Based on the information in the RP-set, all routers in the network can select the proper RP for a specific
IPv6 multicast group based on the following rules:
1. The C-RP that is designated to the smallest IPv6 multicast group range wins.
2. If all the C-RPs are designated to the same IPv6 multicast group range, the C-RP with the highest
priority wins.
3. If all the C-RPs are designated to the same IPv6 multicast group range and have the same priority,
the C-RP with the largest hash value (calculated through the hashing algorithm) wins.
4. If all the C-RPs are designated to the same IPv6 multicast group range and have the same priority
and hash value, the C-RP that has the highest IPv6 address wins.
The hashing algorithm used for RP calculation is "Value (G, M, C
i
) = (1103515245 * ( (1103515245 * (G
& M) + 12345) XOR C
i
) + 12345) mod 2
31
."
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