HP A8800 Configuration Manual page 390

Figure 104 DR election
Source
As shown in
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 becomes 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 wins
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 an 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 through the bootstrap mechanism
to avoid service interruption.
NOTE:
An RP can serve multiple IPv6 multicast groups or all IPv6 multicast groups. Only one RP can serve a
•
given IPv6 multicast group at a time.
A device can serve as a C-RP and a C-BSR at the same time.
•
As shown in
to the BSR. A C-RP-Adv message contains the address and priority of the advertising C-RP and the IPv6
multicast group range it servers. The BSR collects these advertisement messages and chooses the
appropriate C-RP information for each IPv6 multicast group to form an RP-set, which is a database of
DR
Hello message
Register message
Join message
Figure 104, the DR election process is as follows:
Figure 105, each C-RP periodically unicasts its advertisement messages (C-RP-Adv messages)
DR
RP
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Receiver
Receiver