3com S7906E 설치 설명서

1-7 

When the DR fails, a timeout in receiving hello message triggers a new DR election process among the 

other routers. 

The RP is the core of a PIM-SM domain. For a small-sized, simple network, one RP is enough for 

forwarding information throughout the network, and the position of the RP can be statically specified on 

each router in the PIM-SM domain. In most cases, however, a PIM-SM network covers a wide area and 

a huge amount of multicast traffic needs to be forwarded through the RP. To lessen the RP burden and 

optimize the topological structure of the RPT, multiple candidate RPs (C-RPs) can be configured in a 

PIM-SM domain, among which an RP is dynamically elected through the bootstrap mechanism. Each 

elected RP serves a different multicast group range. For this purpose, a bootstrap router (BSR) must be 

configured. The BSR serves as the administrative core of the PIM-SM domain. A PIM-SM domain can 

have only one BSR, but can have multiple candidate-BSRs (C-BSRs). Once the BSR fails, a new BSR 

is automatically elected from the C-BSRs to avoid service interruption. 

 

z 

An RP can serve multiple multicast groups or all multicast groups. Only one RP can serve a given 

multicast group at a time. 

z 

A device can serve 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. A C-RP-Adv message contains the address of the advertising C-RP and the 

multicast group range it serves. The BSR collects these advertisement messages and chooses the 

appropriate C-RP information for each multicast group to form an RP-set, which is a database of 

mappings between multicast groups and RPs. The BSR then encapsulates the RP-set in the bootstrap 

messages it periodically originates and floods the bootstrap messages to the entire PIM-SM domain. 

Figure 1-4 BSR and C-RPs 

 

 

Based on the information in the RP-sets, all routers in the network can calculate the location of the 

corresponding RPs based on the following rules:  

1)  The C-RP with the highest priority wins.