H3C Technologies H3C S10500 Series Switches - Manual (Page 334)

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1. The router chooses an optimal route from the IPv6 unicast routing table and the IPv6 MBGP routing
table, respectively:
○ The router searches its IPv6 unicast routing table by using the IPv6 address of the packet source
as the destination address and automatically selects the optimal route as the RPF route. The
outgoing interface in the corresponding routing entry is the RPF interface and the next hop is the
RPF neighbor. The router considers the path along which the IPv6 multicast packet from the RPF
neighbor arrived on the RPF interface to be the shortest path that leads back to the source.
○ 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 destination 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 match principle, the router selects the longest match route from
these optimal routes. 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 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.
NOTE:
The term packet source can mean different things in different situations:
• For a packet that 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.
• For a packet that traveling along the rendezvous point tree (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 bootstrap router (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 the chapter “IPv6
PIM configuration.”
Implementation of the RPF check 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 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.