Which sequence correctly describes the basic message flow that leads to a successful BGP peering...

RFC 4271 defines the BGP finite state machine as a strict, ordered progression of six states that a session must move through to successfully establish. A newly configured or reset session always begins in Idle, where BGP initializes resources and refuses connections until the ConnectRetry timer fires. From Idle, the router transitions to Connect and attempts to establish the underlying TCP transport session to the configured peer address on port 179. If that TCP attempt does not immediately succeed, the session falls back to the Active state, where the router continues retrying the TCP connection in the background; once the TCP handshake finally completes (from either Connect or Active), the session advances to OpenSent, during which the router transmits its own BGP OPEN message advertising its AS number, hold time, BGP identifier, and capabilities. Upon receiving and validating a compatible OPEN message from the peer, the session moves to OpenConfirm, where both sides exchange KEEPALIVE messages to confirm the parameters negotiated in the OPEN exchange are mutually acceptable. Only after this confirmation does the session reach Established, the final state in which UPDATE messages carrying actual routing information begin to flow between the peers. Any deviation from this Idle → Connect → Active → OpenSent → OpenConfirm → Established ordering, as presented in the other answer choices, does not reflect the standardized BGP state machine. Reference topics: Junos Enterprise Routing – BGP, The BGP Finite State Machine.