104
. The IPv6 multicast forwarding table on Router C contains the (S, G) entry, with VLAN-interface
20 as the RPF interface.
Figure 104 RPF check process
If an IPv6 multicast packet arrives at Router C on VLAN-interface 20, Router C forwards the packet
to all outgoing interfaces.
If an IPv6 multicast packet arrives at Router C on VLAN-interface 10, Router C performs an RPF
check on the packet. Router C searches its IPv6 unicast routing table and finds that the outgoing
interface to 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 packet fails the RPF check, and Router C
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 forwarding across two IPv6 unicast subnets
by establishing a tunnel, for example, an IPv6 over IPv6, or a generic routing encapsulation (GRE)
tunnel between the routers at the edges of the two IPv6 unicast subnets.
For more information about tunneling and GRE, see
Layer 3—IP Services Configuration Guide
.
Figure 105 IPv6 multicast data transmission through a GRE tunnel
Receiver
Receiver
Source
2000::101/16
Router A
Router B
Router C
Vlan-int20
Vlan-int10
Vlan-int10
IPv6 Multicast packets
Destination/Prefix
IPv6 Routing Table on Router C
2000::/16
Interface
Vlan-int20
GRE tunnel
IPv6 unicast router
IPv6 multicast router
Router A
Source
Receiver
Router B
IPv6 multicast router
IPv6 unicast router
IPv6 unicast router
IPv6 unicast router
