Инструкции По Установке для 3com S7906E

1-8 

2)  If all the C-RPs have the same priority, their hash values are calculated through the hashing 

algorithm. The C-RP with the largest hash value wins.  

3)  If all the C-RPs have the same priority and 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

. The table below gives the meanings of the values in this 

algorithm. 

Table 1-1 Values in the hashing algorithm 

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 

 

Figure 1-5 RPT establishment in a PIM-SM domain  

 

 

As shown in 

, the process of building an RPT is as follows:  

1)  When a receiver joins multicast group G, it uses an IGMP message to inform the directly connected 

DR. 

2)  Upon getting the receiver information, the DR sends a join message, which is hop by hop 

forwarded to the RP corresponding to the multicast group.  

3)  The routers along the path from the DR to the RP form an RPT branch. Each router on this branch 

generates a (*, G) entry in its forwarding table. The * means any multicast source. The RP is the 

root, while the DRs are the leaves, of the RPT.