3Com 7757 Configuration Manual page 467

3com switch 7750 family

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One or more candidate BSRs must be configured in a PIM domain. Through the

auto-election, the candidate BSRs elect a BSR which is responsible for collecting

and advertising RP information. The auto-election among candidate BSRs is

described in the following section:

Specify a PIM-SM-enabled interface when configuring a router as a candidate

Each candidate BSR considers itself as the BSR of the PIM-SM and uses the IP

address of the specified interface as the BSR address to send Bootstrap

When the candidate BSR receives Bootstrap messages from other routers, it will

compare the BSR address in the received Bootstrap message with its own BSR

address in priority and IP address. When the priority is the same, the candidate

BSR with a higher IP address is considered to be better. If the former is better,

the candidate BSR will replace its own BSR address with the new BSR address

and does not consider itself as BSR any more. Otherwise, the candidate BSR will

keep its own BSR address and continue to consider itself as BSR.

The positions of RPs and BSRs in the network are as shown in Figure 115:

Figure 115 Diagram for the communication between RPs and BSRs

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Only one BSR can be elected in a network or management domain, while multiple

candidate BSRs (C-BSR) can be configured. In this case, once the BSR fails, other

C-BSRs can elect a new BSR through auto-election. Thus, the service is prevented

from being interrupted.

In the same way, multiple C-RPs can be configured in a PIM-SM domain, the RP

corresponding to each multicast group is worked out through the BSR mechanism.

RPT building

Assume the receiver hosts are User B, User D, and User E. When a receiver host

joins in a multicast group G, it will inform the leaf router directly connected to the

host through IGMP packets. Thus the leaf router masters the receiver information

of the multicast group G, and then the leaf router will send Join messages to the

upper-layer nodes in the direction of RP, as shown in Figure 116:

PIM Overview

Troubleshooting

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