HP A8800 Configuration Manual page 395

The working mechanism of IPv6 BIDIR-PIM is summarized as follows:
• Neighbor discovery
RP discovery
•
DF election
•
• Bidirectional RPT building
Neighbor discovery
IPv6 BIDIR-PIM uses the same neighbor discovery mechanism as IPv6 PIM-SM does. For more information,
see "Neighbor
RP discovery
IPv6 BIDIR-PIM uses the same RP discovery mechanism as IPv6 PIM-SM does. For more information, see
"RP discovery." In IPv6 BIDIR-PIM, an RPF interface is the interface pointing to an RP, and an RPF
neighbor is the address of the next hop to the RP.
In IPv6 PIM-SM, an RP must be specified with a real IPv6 address. In IPv6 BIDIR-PIM, however, an RP can
be specified with a virtual IPv6 address, which is called the rendezvous point address (RPA). The link
corresponding to the RPA's subnet is called the rendezvous point link (RPL). All interfaces connected to
the RPL can act as RPs, which back up one another.
DF election
On a network segment with multiple multicast routers, the same multicast packets may be forwarded to
the RP repeatedly. To address this issue, IPv6 BIDIR-PIM uses a DF election mechanism to elect a unique
designated forwarder (DF) for each RP on every network segment within the IPv6 BIDIR-PIM domain, and
allows only the DF to forward multicast data to the RP.
DF election is not necessary for an RPL.
Figure 108 DF election
As shown in
multicast packets from Route A, and they may both forward the packets to downstream routers on the
local subnet. As a result, the RP (Router E) receives duplicate multicast packets. With the DF election
mechanism, once receiving the RP information, Router B and Router C initiate a DF election process for
the RP:
discovery."
Figure 108, without the DF election mechanism, both Router B and Router C can receive
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