H3C Technologies H3C S7500E Series Switches - Manual (Page 312)

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routing table based on the configured multicast routing and forwarding policy and installs the
route entry into its IPv6 multicast forwarding table.
RPF Check Mechanism
An IPv6 multicast routing protocol relies on the existing IPv6 unicast routing information or IPv6
MBGP routes in creating IPv6 multicast routing entries. When creating IPv6 multicast routing
table entries, an IPv6 multicast routing protocol uses the reverse path forwarding (RPF) check
mechanism to ensure 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.