H3C LS-3100-52P-OVS-H3 Operation Manual - page 1102
1-2
IPv6 multicast data delivery along the correct path. In addition, the RPF check mechanism also helps
avoid data loops caused by various reasons.
RPF Check process
The basis for an RPF check is an IPv6 unicast route or an IPv6 MBGP route.
z
An IPv6 unicast routing table contains the shortest path to each destination subnet;
z
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:
1) The router first chooses an optimal route from the IPv6 unicast routing table and IPv6 MBGP
routing table respectively:
z
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.
z
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.
2) Then, the router selects one from these two optimal routes as the RPF route. The selection process
is as follows:
z
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.
z
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.
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 Volume.