H3C Technologies H3C SecPath F1000-E - Manual (Page 155)

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An IPv6 MBGP routing table contains IPv6 multicast routing information.
When performing an RPF check, a router searches its IPv6 unicast routing table and IPv6 MBGP routing
table at the same time. The specific process is as follows:
The router first chooses an optimal route from the IPv6 unicast routing table and IPv6 MBGP routing table
respectively:
The router searches its IPv6 unicast routing table 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,
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.
Then, the router selects one from these two 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 the two;
if these two routes have the same prefix length, the router selects the route with a higher priority; if these
two 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 two routes have the same priority, the router selects the IPv6 MBGP route as the RPF route.
NOTE:
The above-mentioned “packet source” can mean different things in different situations:
• 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.
• 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.
• 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, RP and BSR, see IPv6 PIM Configuration in the IP
Multicast Volume.
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.