The multicast BFD session uses multicast packets and is not affected by the protocol status on an interface. When the BFD session goes Down and the protocol status on the interface changes to BFD Status Down, multicast BFD packets can still be sent. After the link recovers, the multicast BFD session can become Up through negotiation. As a result, the interface is unlocked and becomes Up. Unicast packets, however, cannot be sent or received after the protocol status on the interface goes Down, which causes deadlock.
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