R3303-HP HSR6800 Routers IP Multicast Configuration Guide

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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 on a router at the RP side, 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

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 94 DF election

As shown in Figure 94, without the DF election mechanism, both Router B and Router C can receive

multicast packets from Route A, and they might 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:

1. Router B and Router C multicast DF election messages to all PIM routers (224.0.0.13). The election

messages carry the RP's address, and the priority and metric of the unicast route, MBGP route, or

multicast static route to the RP.

2. The router with a route of the highest priority becomes the DF.

Ethernet

Router B Router C

Router A

IPv6 Multicast packets

DF election message

Source

Router DRouter E