What are the TCP client states?

The TCP client states represent the different stages a TCP connection goes through on the client-side, from initiation to termination. Here's a breakdown:

TCP Client States Explained

The following table outlines the primary TCP client states, drawing on the information provided:

State	Description
CLOSED	Initial state. The client has no active TCP connection. This is where the client starts before initiating a connection.
SYN_SENT	Client request connection. After the client sends a connection request (SYN packet) to the server, it enters this state, waiting for a response.
ESTABLISHED	Done. The TCP connection is successfully established, and data can be transmitted between the client and the server.
FIN-WAIT-1	The client has sent a FIN packet to the server, indicating it wants to close the connection and is waiting for an ACK.
FIN-WAIT-2	The client has received an ACK for its FIN packet and is now waiting for a FIN packet from the server.
TIME-WAIT	The client is waiting for a sufficient time to pass to ensure the remote TCP received the acknowledgment of its connection termination request.
CLOSING	The client is waiting for an acknowledgment of the last ACK sent.
CLOSE-WAIT	The client has received a FIN packet from the server but hasn't yet sent its own FIN packet. This means the application is still running.
LAST-ACK	The client is waiting for the final ACK to its FIN packet that was sent to close the connection.

Note: Listen and SYN_Recv are states primarily associated with the server, not the client. The client initiates the connection by moving from CLOSED to SYN_SENT.

Practical Insights

• Troubleshooting: Understanding TCP states is crucial for diagnosing network issues. For example, a client stuck in SYN_SENT might indicate a firewall problem or a server that's not responding.
• Connection Management: Properly managing TCP connections, including closing them when they're no longer needed, is important for resource utilization and preventing issues like port exhaustion.