What is an RPF check？
正确答案:
Forwarding multicast traffic away from the source， rather than to the receiver， is called Reverse Path Forwarding （RPF）. RPF check helps to guarantee that the distribution tree will be loop-free.
RPF rules：
If a router receives a multicast packet on an interface that it uses to send unicast packets to the multicast source， then the multicast packet has arrived on the RPF interface. （定义RPF接口）
If the multicast packet arrives on the RPF interface， the router forwards the packet out the interfaces that are present in the outgoing interface list of a multicast routing table entry. （入接口是RPF接口的处理）
If the multicast packet does not arrive on the RPF interface， the packet is silently discarded（入接口不是RPF接口的处理）
RPF rules：
If a router receives a multicast packet on an interface that it uses to send unicast packets to the multicast source， then the multicast packet has arrived on the RPF interface. （定义RPF接口）
If the multicast packet arrives on the RPF interface， the router forwards the packet out the interfaces that are present in the outgoing interface list of a multicast routing table entry. （入接口是RPF接口的处理）
If the multicast packet does not arrive on the RPF interface， the packet is silently discarded（入接口不是RPF接口的处理）
答案解析:有
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