H3C S5500-EI Configuration Manual page 390

In the case of a multi-access network, a DR must be elected, no matter this network connects to IPv6
multicast sources or to receivers. The DR at the receiver side sends join messages to the RP; the DR at the
IPv6 multicast source side sends register messages to the RP.
A DR is elected on a multi-access subnet by means of comparison of the priorities and IPv6 link-local
addresses carried in hello messages.
MLD must be enabled on a device that acts as a receiver-side DR before receivers attached to this device
can join IPv6 multicast groups through this DR.
For more information about MLD, see
Figure 94 DR election
As shown in
Routers on the multi-access network send hello messages to one another. The hello messages
1.
contain the router priority for DR election. The router with the highest DR priority will become the
DR.
In the case of a tie in the router priority, or if any router in the network does not support carrying
2.
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. 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 C-RPs
in an IPv6 PIM-SM domain. Among them, an RP is dynamically elected through the bootstrap mechanism.
Each elected RP is designated to a different multicast group range. For this purpose, you must configure
Figure 94, the DR election process is as follows:
"Configuring MLD (available only on the
371
S5500-EI)."