H3C LS-3100-52P-OVS-H3 Operation Manual page 1103

Implementation of the RPF check in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast data packet would bring a big burden to
the router. The use of an IPv6 multicast forwarding table is the solution to this issue. When creating an
IPv6 multicast routing entry and an IPv6 multicast forwarding entry for an IPv6 multicast packet, the
router sets the RPF interface of the packet as the incoming interface of the (S, G) entry. Upon receiving
an (S, G) IPv6 multicast packet, the router first searches its IPv6 multicast forwarding table:
1) If the corresponding (S, G) entry does not exist in the IPv6 multicast forwarding table, the packet is
subject to 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 on which the packet actually arrived is the RPF interface, the RPF check succeeds
and the router forwards the packet to all the outgoing interfaces.
If the interface on which the packet actually arrived 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 on which the packet actually arrived 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 on which the packet actually arrived is not
the incoming interface in the IPv6 multicast forwarding table, the IPv6 multicast packet is subject to
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 is to be discarded.
If the RPF interface is not the incoming interface, this means the (S, G) entry has expired, and
router replaces the incoming interface with the RPF interface. If the interface on which the packet
arrived in 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
1-1. The IPv6 multicast forwarding table on Router C contains the (S, G) entry, with Vlan-interface 20 as
the RPF interface.
Figure 1-1 RPF check process
When an IPv6 multicast packet arrives on Vlan-interface 20 of Router C, as the interface is the
incoming interface of the (S, G) entry, the router forwards the packet to all outgoing interfaces.
1-3
Figure