H3C Technologies H3C S7500E Series Switches - Manual (Page 86)

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on the configured multicast routing and forwarding policy and adds the route entry into its
multicast forwarding table.
RPF Check Mechanism
A multicast routing protocol relies on the existing unicast routing information, MBGP routes, or
multicast static routes in creating multicast routing entries. When creating multicast routing
table entries, a multicast routing protocol uses the reverse path forwarding (RPF) check
mechanism to ensure 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 a unicast route, an MBGP route, or a multicast static route.
z A unicast routing table contains the shortest path to each destination subnet,
z An MBGP routing table contains multicast routing information, and
z A multicast static routing table contains the RPF routing information defined by the user
through static configuration.
When performing an RPF check, a router searches its unicast routing table and multicast static
routing table at the same time. The specific process is as follows:
1) The router first chooses an optimal route from the unicast routing table, MBGP routing table,
and multicast static routing table:
z The router automatically chooses an optimal unicast route by searching its unicast routing
table, using the IP 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. The router considers the path along which the 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 MBGP route by searching its MBGP routing
table, using the IP 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.
z The router automatically chooses an optimal multicast static route by searching its
multicast static routing table, using the IP address of the “packet source” as the destination
address. The corresponding routing entry explicitly defines the RPF interface and the RPF
neighbor.
2) Then, the router selects one from these three 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 three; if these three routes have the same mask, the router selects the route with
the highest priority; if the three routes have the same priority, the router selects the RPF
route according to the sequence of multicast static route, MBGP route, and unicast route.
z If not configured to use the longest match principle, the router selects the route with the
highest priority; if the three routes have the same priority, the router selects the RPF route
according to the sequence of multicast static route, MBGP route, and unicast route.