H3C S5500-EI Series Operation Manual page 201

Operation Manual – Multicast
H3C S5500-EI Series Ethernet Switches
unicast route; instead, it relies on the existing unicast routing information or multicast
static routes in creating multicast routing entries.
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 and
multicast static routing table:
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.
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 two optimal routes as the RPF route. The
selection 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 mask, the route
selects the route with a higher priority; if the two routes have the same priority, the
router selects the multicast static route.
If not configured to use the longest match principle, the router selects the route
with a higher priority; if the two routes have the same priority, the router selects the
multicast static 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 source-based tree from the multicast source to the
rendezvous point (RP), "packet source" means the multicast source.
For a packet traveling along the rendezvous point tree (RPT) from the RP to the
receivers, "packet source" means the RP.
For a bootstrap message from the bootstrap router (BSR), "packet source" means
the BSR.
For details about the concepts of SPT, RPT and BSR, refer to
Assume that unicast routes exist in the network and no multicast static routes have
been configured on Switch C, as shown in
SPT from the multicast source to the receivers.
Figure 9-1. Multicast packets travel along the
9-3
Chapter 9 Multicast Routing and
Forwarding Configuration
PIM Configuration.