H3C Technologies H3C S12500-X Series Switches - Manual (Page 159)

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IMPORTANT:
MLD must be enabled on the device that acts as the receiver-side DR. Otherwise, the receiver hosts
attached to the DR cannot join any IPv6 multicast groups. For more information about MLD, see
"
Configuring MLD ."
Figure 46 DR election
As shown in Figure 25 , the DR election process is as follows:
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. In the case of a tie in the 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.
If the DR fails, its IPv6 PIM neighbor lifetime expires, and the other routers initiate a new DR election.
RP discovery
An RP is the core of an IPv6 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 IPv6 PIM-SM domain. However, in an IPv6 PIM-SM network that covers a wide area, a huge amount
of IPv6 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 an IPv6 PIM-SM domain and use
the bootstrap mechanism to dynamically elect RPs. An elected RP provides services for a different IPv6
multicast group. For this purpose, you must configure a bootstrap router (BSR). A BSR serves as the
administrative core of an IPv6 PIM-SM domain. An IPv6 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 IPv6 multicast groups, but an IPv6 multicast group only uses one
RP.
• A device can act as a C-RP and a C-BSR at the same time.