H3C Technologies H3C S12500 Series Switches - Manual (Page 390)

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Figure 102 DR election
As shown in Figure 102 , 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 must be forwarded through the RP. To
lessen the RP burden and optimize the topological structure of the RPT, you can configure multiple
candidate RPs (C-RPs) in an IPv6 PIM-SM domain. Among them, an RP is dynamically elected through the
bootstrap mechanism. Each elected RP provides services for a different multicast group range. For this
purpose, you must configure a bootstrap router (BSR). 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). If the BSR fails, a new BSR is automatically elected from the C-BSRs to avoid
service interruption.
NOTE:
•
An RP can provide services for IPv6 multiple multicast groups or all IPv6 multicast groups. Only one RP
can provide services for 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 Figure 103 , 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 to which it is designated. 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