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through the RP to the receivers along the bidirectional RPT. In this case, each router needs to maintain
only a (*, G) multicast routing entry, saving system resources.
IPv6 BIDIR-PIM is suitable for networks with dense multicast sources and dense receivers.
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 discovery."
RP discovery
IPv6 BIDIR-PIM uses the same RP discovery mechanism as IPv6 PIM-SM does. For more information, see
"RP discovery."
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.
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.
DF election
On a network segment with multiple multicast routers, the same multicast packets might 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.
NOTE:
DF election is not necessary for an RPL.
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