HP FlexNetwork 7500 Series Configuration Manual page 285

The router checks whether the packet arrived at the RPF interface. If yes, the RPF check
3.
succeeds and the packet is forwarded. If not, the RPF check fails and the packet is discarded.
RPF check implementation in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast packet would heavily burden the router.
The use of an IPv6 multicast forwarding table is the solution to this issue. When the router creates an
IPv6 multicast forwarding entry for an IPv6 (S, G) packet, it sets the RPF interface of the packet as
the incoming interface of the (S, G) entry. After the router receives another (S, G) packet, it looks up
its IPv6 multicast forwarding table for a matching (S, G) entry:
•
If no match is found, the router first determines the RPF route back to the packet source. Then,
it creates a forwarding entry with the RPF interface as the incoming interface and performs one
of the following tasks:
If the receiving interface is the RPF interface, the RPF check succeeds and the router
forwards the packet out of all outgoing interfaces.
If the receiving interface is not the RPF interface, the RPF check fails and the router
discards the packet.
•
If a match is found and the matching forwarding entry contains the receiving interface, the
router forwards the packet out of all outgoing interfaces.
•
If a match is found but the matching forwarding entry does not contain the receiving interface,
the router determines the RPF route back to the packet source. Then, the router performs one
of the following tasks:
If the RPF interface is the incoming interface, it means that the forwarding entry is correct
but the packet traveled along a wrong path. The packet fails the RPF check, and the router
discards the packet.
If the RPF interface is not the incoming interface, it means that the forwarding entry has
expired. The router replaces the incoming interface with the RPF interface and matches the
receiving interface against the RPF interface. If the receiving interface is the RPF interface,
the router forwards the packet out of all outgoing interfaces. Otherwise, it discards the
packet.
Figure 85 RPF check process
IPv6 Routing Table on Router C
Destination/Prefix
2000::/16
Source
2000::101/16
As shown in
not configured. IPv6 multicast packets travel along the SPT from the multicast source to the
receivers. The IPv6 multicast forwarding table on Router C contains the (S, G) entry, with
GigabitEthernet 1/0/2 as the RPF interface.
Interface
GE1/0/2
Router A
IPv6 Multicast packets
Figure 85, assume that IPv6 unicast routes are available on the network. IPv6 MBGP is
Router B
GE1/0/1
GE1/0/1
GE1/0/2
Router C
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Receiver
Receiver