124
Figure 43 Information exchange between C-RPs and the BSR
Based on the information in the RP-sets, all routers in the network can select the proper RP for a
specific multicast group based on the following rules:
1.
The C-RP that is designated to the smallest multicast group range wins.
2.
If the C-RPs are designated to the same 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 IP 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 7 Values in the hashing algorithm
Value Description
Value
Hash value.
G
IP address of the multicast group.
M
Hash mask length.
C
i
IP address of the C-RP.
&
Logical operator of "and."
XOR
Logical operator of "exclusive-or."
Mod
Modulo operator, which gives the remainder of an integer division.
