H3C S7500 Series Operation Manual page 434

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
In order to guarantee the transmission of multicast packets in the network, multicast
packets must be forwarded based on unicast routing tables or those specially provided
to multicast (such as MBGP multicast routing tables). In addition, to prevent the
interfaces from receiving the same information from different peers, routers must check
the receiving interfaces. This check mechanism is reverse path forwarding (RPF) check,
which is the basis of performing multicast forwarding for most multicast routing
protocols.
Based on the source address, a multicast router judges whether a multicast packet
comes from the specified interface, that is, RPF check determines whether the inbound
interface is correct by comparing the interface receiving the packet with the interface
that must receive the packet. If the router resides on a shortest path tree (SPT), the
interface that must receive the multicast packet points to the multicast source. If the
router resides on a rendezvous point tree (RPT), the interface that must receive the
multicast packet points to the rendezvous point (RP). When a multicast data packet
reaches the router, if RPF check passes, the router forwards the data packet based on
its multicast forwarding entry; otherwise, the data packet is dropped.
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Chapter 1 Multicast Overview