H3C Technologies H3C S12500 Series Switches - Manual (Page 348)

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{
The router automatically chooses an optimal IPv6 MBGP route by searching its MBGP routing
table, and using the IPv6 address of the packet source as the source address. The outgoing
interface in the corresponding routing entry is the RPF interface and the next hop is the RPF
neighbor.
2. The router selects one of these optimal routes as the RPF route. The selection process is as follows:
{
If configured to use the longest prefix match principle, the router selects the longest prefix match
route from the two. If these routes have the same prefix length, the router selects the route with
a higher priority. If these routes have the same priority, the router selects the IPv6 MBGP route
as the RPF route.
{
If not configured to use the longest prefix match principle, the router selects the route with a
higher priority. If these routes have the same priority, the router selects the IPv6 MBGP route as
the RPF route.
The term "packet source" means different things in different situations:
• For a packet that travels along the SPT from the multicast source to the receivers or the rendezvous
point (RP), the packet source for RPF check is the multicast source.
• For a packet that travels along the RPT from the RP to the receivers, or along the source-side RPT from
the multicast source to the RP, the packet source for RPF check is the RP.
• For a bootstrap message from the BSR, the packet source for RPF check is the BSR.
For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see "Configuring IPv6
PIM."
RPF check implementation in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast data packet would heavily burden 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. After 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
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 on which the packet arrived is the RPF interface, the RPF check succeeds and the
router forwards the packet out of all the outgoing interfaces.
{
If the interface on which the packet 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 out of 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 undergoes
an RPF check.
{
If the RPF interface is the incoming interface of the (S, G) entry, it means that 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, it means that the (S, G) entry has expired, and
router replaces the incoming interface with the RPF interface. If the interface on which the