R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

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Figure 39 RPF check process
As shown in Figure 39, assume that IPv6 unicast routes are available in the network, and IPv6 multicast
packets travel along the SPT from the multicast source to the receivers. The IPv6 multicast forwarding table
on Switch C contains the (S, G) entry, with Vlan-interface 20 as the RPF interface.
• When Vlan-interface 20 of Switch C receives an IPv6 multicast packet, because the interface is the
incoming interface of the (S, G) entry, the switch forwards the packet out of all outgoing interfaces.
• When Vlan-interface 10 of Switch C receives an IPv6 multicast packet, because the interface is not
the incoming interface of the (S, G) entry, the switch performs an RPF check on the packet. The
switch searches its IPv6 unicast routing table and finds that the outgoing interface to the source (the
RPF interface) is Vlan-interface 20. This means that the (S, G) entry is correct but the packet traveled
along a wrong path. The RPF check fails and the switch discards the packet.
IPv6 multicast forwarding across IPv6 unicast subnets
Routers forward the IPv6 multicast data from an IPv6 multicast source hop by hop along the forwarding
tree, but some routers might not support IPv6 multicast protocols in a network. When the IPv6 multicast
data is forwarded to a router that does not support IPv6 multicast, the forwarding path is blocked. In this
case, you can enable IPv6 multicast data forwarding across the IPv6 unicast subnets by establishing a
tunnel between the routers at both ends of the IPv6 unicast subnets.
Receiver
Receiver
Source
2000::101/16
Switch A
Switch B
Switch C
Vlan-int20
Vlan-int10
Vlan-int10
IPv6 Multicast packets
Destination/Prefix
IPv6 Routing Table on Switch C
2000::/16
Interface
Vlan-int20