Which BGP state is the one where BGP initiates the TCP connection and sends an Open message to the sender?

The Connect state in BGP (Border Gateway Protocol) is a bit earlier in the process of establishing a BGP session than the OpenSent state. In the Connect state, the router is attempting to establish a TCP connection with its BGP peer. If the TCP connection attempt is successful, the BGP state machine moves to the OpenSent state, where the router sends an Open message to the BGP peer to initiate the BGP session.

Here’s a simplified sequence of the BGP states leading to a session establishment:

1. Idle: The initial state where BGP waits to start the peering process.
2. Connect: The router is attempting to establish a TCP connection with the peer. If successful, it moves to OpenSent; if unsuccessful, it may retry the connection attempt or fall back to the Idle state.
3. OpenSent: Once the TCP connection is established, the router sends an Open message to the peer, moving the process to the next stage.

So, while the OpenSent state is where the Open message is sent following a successful TCP connection, the Connect state is specifically focused on establishing that TCP connection itself before any BGP messages are exchanged.