What occurs in the idle state for BGP?

• A. The router is searching the IP routing table to see whether a route exists to reach the neighbor
• B. The router is establishing a TCP session with the neighbor
• C. The router exchanges keepalive messages
• D. The router processes BGP updates

Answer: (A)

In the idle state, BGP isn’t yet talking to the neighbor. The router is essentially waiting and checking whether it has a reachable path to the neighbor by looking up the neighbor’s IP in its IP routing table. If a route to reach the neighbor exists, the BGP FSM will move toward establishing a TCP session to that neighbor; if not, it stays idle until a route becomes available. No TCP session is started, no updates are exchanged, and no keepalive messages are sent in this state. Those actions occur once the session starts and the state progresses to the connect/established phases.