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incoming interface of the (S, G) entry with the interface that received the packet and forwards
the packet out of all the outgoing interfaces.
CAUTION:
You can configure special processing of packets that have failed an RPF check instead of simply dropping
them. For more information, see "
Configuring RPF check failure processing
Assume that IPv6 unicast routes are available in the network, IPv6 MBGP is not enabled, as shown
. IPv6 multicast packets travel along the SPT from the multicast source to the receiver hosts.
The IPv6 multicast forwarding table on Router C contains the (S, G) entry, with POS 2/1/2 as the RPF
interface.
Figure 90
RPF check process
•
When a multicast packet arrives on POS 2/1/2 of Router C, as the interface is the incoming
interface of the (S, G) entry, the router forwards the packet out of all outgoing interfaces.
•
When a multicast packet arrives on POS 2/1/1 of Router C, as the interface is not the incoming
interface of the (S, G) entry, the router performs an RPF check on the packet: The router searches its
IPv6 unicast routing table and finds that the outgoing interface to the source (the RPF interface) is
POS 2/1/2. This means the (S, G) entry is correct and packet arrived along a wrong path. The RPF
check fails and the packet is discarded.
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
generic routing encapsulation (GRE) tunnel between the routers at both ends of the IPv6 unicast subnets.
For more information about GRE, see
Layer 3—IP Services Configuration Guide
.
Receiver
Receiver
Source
2000::101/16
Router A
Router B
Router C
POS2/1/2
POS2/1/1
POS2/1/1
IPv6 Multicast packets
Destination/Prefix
IPv6 Routing Table on Router C
2000::/16
Interface
POS2/1/2