330
1.
If the corresponding (S, G) entry does not exist in the IPv6 multicast forwarding table, the packet
undergoes an RPF check. The router creates an IPv6 multicast routing entry based on the relevant
routing information and installs the entry into the IPv6 multicast forwarding table, with the RPF
interface as the incoming interface.
{ If the interface that received the packet is the RPF interface, the RPF check succeeds and the
router forwards the packet to all the outgoing interfaces.
{ If the interface that received the packet is not the RPF interface, the RPF check fails and the
router discards the packet.
2. If the corresponding (S, G) entry exists, and the interface that received the packet is the incoming
interface, the router forwards the packet to all the outgoing interfaces.
3. If the corresponding (S, G) entry exists, but the interface that received the packet is not the
incoming interface in the IPv6 multicast forwarding table, the IPv6 multicast packet undergoes an
RPF check.
{ If the RPF interface is the incoming interface of the (S, G) entry, this means the (S, G) entry is
correct but the packet arrived from a wrong path. The packet will be discarded.
{ If the RPF interface is not the incoming interface, this means that the (S, G) entry has expired,
and the router replaces the incoming interface with the RPF interface. If the interface on which
the packet arrived is the RPF interface, the router forwards the packet to all the outgoing
interfaces. Otherwise it discards the packet.
Assume that IPv6 unicast routes are available in the network, IPv6 MBGP is not configured, and IPv6
multicast packets travel along the SPT from the multicast source to the receivers, as shown in Figure 82.
T
he IPv6 multicast forwarding table on Router C contains the (S, G) entry, with VLAN-interface 20 as the
RPF interface.
Figure 82 RPF check process
• When an IPv6 multicast packet arrives on VLAN-interface 20 of Router C, because the interface is
the incoming interface of the (S, G) entry, the router forwards the packet to all outgoing interfaces.
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
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