H3C Technologies H3C S7500E Series Switches - Manual (Page 313)

11-3
The above-mentioned “packet source” can mean different things in different situations:
z For a packet traveling along the shortest path tree (SPT) from the multicast source to the
receivers or the rendezvous point (RP), the “packet source” for RPF check is the multicast
source.
z For a packet traveling along the rendezvous point tree (RPT) from the RP to the receivers,
the “packet source” for RPF check is the RP.
z For a bootstrap message from the bootstrap router (BSR), the “packet source” for RPF
check is the BSR.
For details about the concepts of SPT, RPT, RP and BSR, refer to IPv6 PIM Configuration in
the IP Multicast Configuration Guide.
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.
z 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.
z 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.
z 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.
z 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