Open state description: which statement is accurate?

• A. An open message was sent with the parameters for the BGP session.
• B. The router found a route to the neighbor and has completed the three-way handshake.
• C. The router received agreement on the parameters for establishing a session.
• D. Peering is established and routing begins.

Answer: (A)

Open state is the phase where BGP begins negotiating the session itself after the TCP connection is up. The key action is sending an OPEN message that carries the session parameters: your AS number, the hold time, the BGP identifier, and any capabilities. This is what marks the transition into the OpenSent/Open state—as soon as that OPEN is sent, the router is signaling its intent to establish a BGP session and negotiate how they will talk. The TCP three-way handshake is a separate, earlier layer event that must complete before BGP can proceed, so describing the open state as tied to the TCP handshake isn’t accurate. Peering isn’t fully established until later, after the OPEN exchange and subsequent KEEPALIVE processing, and routing updates begin only in the Established state. Agreement on parameters does happen in concert with exchanging OPEN messages, but the defining moment of the Open state is sending the OPEN with the session parameters.