What does the 'Established' neighbor state indicate?

• A. Initial TCP connection attempt
• B. The BGP session is closing
• C. Update, Keepalive and Notification messages are exchanged
• D. Session is idle

Answer: (C)

Established means the BGP session has completed the TCP connection and the BGP OPEN negotiation, so the neighbor relationship is fully formed and routing information can be exchanged. In this state, peers send Update messages to advertise new routes or withdraw existing ones, Keepalive messages to confirm the session is still alive within the configured hold time, and Notification messages only when an error occurs. This combination of message types is what allows the routers to share routing information and maintain the session. Earlier phases involve establishing the TCP connection and negotiating OPEN, while the idle state or a closing state are not used for regular route exchanges.