407
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
, 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 119 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 the C-RPs are designated to the same IPv6 multicast group range, the C-RP with the highest
priority wins.
3.
If the C-RPs have the same priority, the C-RP with the largest hash value wins. The hash value
is calculated through the hashing algorithm.
4.
If the C-RPs have the same hash value, the C-RP with 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
."
Table 12 Values in the hashing algorithm
Value Description
Value
Hash value.
G
The digest from the exclusive-or (XOR) operation between the 32-bit segments of the
IPv6 multicast group address. For example, if the IPv6 multicast address is
FF0E:C20:1A3:63::101, G = 0xFF0E0C20 XOR 0x01A30063 XOR 0x00000000 XOR
0x00000101.
M
Hash mask length.
C
i
The digest from the exclusive-or (XOR) operation between the 32-bit segments of the
C-RP IPv6 address. For example, if the IPv6 address of the C-RP is
3FFE:B00:C18:1::10, C
i
= 0x3FFE0B00 XOR 0x0C180001 XOR 0x00000000 XOR
