Comprehensive and Detailed In-Depth Explanation:
BFD (Bidirectional Forwarding Detection) detects link failures faster than traditional mechanisms.
Session states during setup:
AdminDown → Initial state (session is administratively disabled).
Down → The session is being established but has not yet exchanged valid control packets.
Init → The session is partially established (one side has detected the peer).
Up → The session is fully operational (not part of the setup process).
Since AdminDown, Down, and Init are involved in session setup, the correct answers are B, C, D.
???? Reference: Huawei HCIA-Datacom Study Guide, BFD Session Establishment and States.
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