The last keepalive is less than 3 times the negotiated holddown timer. -->established
The router has not received a response. The neighbor might be unreachable. -->active
The router is waiting for an initial response from the neighbor. -->connect
The router starts listening for a connection. -->idle
This question requires matching specific BGP connection states from the BGP Finite State Machine (FSM) to descriptions of the router's activity or condition in those states.
Idle:This is the starting state. The BGP process is administratively up but is not actively trying to connect. It refuses all incoming BGP connection attempts but listens for a start event (like configuration or operator initiation) or potentially listens for incoming connections if configured for passive peering.
Matches:"The router starts listening for a connection." (This describes the passive aspect of the Idle state before active attempts begin).
Connect:In this state, BGP is actively trying to establish a TCP connection with the peer. It has initiated the TCP three-way handshake and is waiting for it to complete, or it is waiting for a remote peer to initiate the TCP connection.
Matches:"The router is waiting for an initial response from the neighbor." (Specifically, waiting for the TCP handshake to complete).
Active:If the TCP connection attempt in the Connect state fails (e.g., timeout), the router transitions to the Active state. In this state, it will periodically retry establishing the TCP connection while also listening for an incoming connection from the peer. This state indicates repeated failures to establish TCP connectivity.
Matches:"The router has not received a response. The neighbor might be unreachable." (This reflects the condition in the Active state where connection attempts fail, suggesting the neighbor is unreachable at the TCP level).
Established:This is the final, operational state where the TCP connection is up, BGP session parameters have been successfully negotiated via OPEN messages, and KEEPALIVE messages are being exchanged. Routing information (UPDATEs) can be exchanged. The condition described implies the session is healthy and timers are being maintained.
Matches:"The last keepalive is less than 3 times the negotiated holddown timer." (While phrased slightly unusually, this indicates the holddown timer hasnotexpired because keepalives are being received within the expected window (Holddown Timer = ~3 * Keepalive Interval). This confirms the session is alive, which is true in the Established state).
