HP 6125XLG Ip Multicast Configuration Manual page 96

Figure 34 DR election
As shown in
1. The routers on the shared-media LAN send hello messages to one another. The hello messages
contain the priority for DR election. The router with the highest DR priority is elected as the DR.
2. The router with the highest IP address wins the DR election under one of following conditions:
All the routers have the same DR election priority.
A router does not support carrying the DR-election priority in hello messages.
If the DR fails, its PIM neighbor lifetime expires and the other routers will initiate to elect a new DR.
RP discovery
An RP is the core of a PIM-SM domain. For a small-sized, simple network, one RP is enough for multicast
forwarding throughout the network. In this case, you can specify a static RP on each router in the PIM-SM
domain. However, in a PIM-SM network that covers a wide area, a huge amount of multicast data is
forwarded by the RP. To lessen the RP burden and optimize the topological structure of the RPT, you can
configure multiple candidate-RPs (C-RPs) in a PIM-SM domain. An RP is dynamically elected from the
C-RPs by the bootstrap mechanism. An elected RP provides services for a different multicast group. For
this purpose, you must configure a bootstrap router (BSR). A BSR serves as the administrative core of a
PIM-SM domain. A PIM-SM domain has only one BSR, but can have multiple candidate-BSRs (C-BSRs) so
that, if the BSR fails, a new BSR can be automatically elected from the C-BSRs and avoid service
interruption.
NOTE:
An RP can provide services for multiple multicast groups, but a 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
to the BSR. An advertisement message contains the address of the advertising C-RP and the 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 multicast groups and RPs. The
BSR encapsulates the RP-set information in the bootstrap messages (BSMs) and floods the BSMs to the
entire PIM-SM domain.
Figure 34, the DR election process is as follows:
Figure 35, each C-RP periodically unicasts its advertisement messages (C-RP-Adv messages)
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