H3C Technologies H3C SecPath F1000-E - Manual (Page 169)

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Figure 3 DR election
Join message
RP DR
DR
Hello message
Register message
Source
Receiver
Receiver
As shown in
Figure 3 , the DR election process is as follows:
1. Routers on the multi-access network send hello messages to one another. The hello messages
contain the router priority for DR election. The router with the highest DR priority will become the
DR.
2. In the case of a tie in the router priority, or if any router in the network does not support carrying
the DR-election priority in hello messages, The router with the highest IPv6 link-local address will
win the DR election.
When the DR works abnormally, a timeout in receiving hello message triggers a new DR election process
among the other routers.
RP discovery
The RP is the core of an IPv6 PIM-SM domain. For a small-sized, simple network, one RP is enough for
forwarding IPv6 multicast information throughout the network, and the position of the RP can be statically
specified on each router in the IPv6 PIM-SM domain. In most cases, however, an IPv6 PIM-SM network
covers a wide area and a huge amount of IPv6 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 an IPv6 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 IPv6 PIM-SM
domain. An IPv6 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.
NOTE:
•
An RP can serve IPv6 multiple multicast groups or all IPv6 multicast groups. Only one RP can serve a
given IPv6 multicast group at a time.
• A device can server as a C-RP and a C-BSR at the same time.
As shown in the figure below, 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 IPv6
multicast group range it serves. The BSR collects these advertisement messages and chooses the