Which sequence represents the TCP four-way handshake for connection termination?

• A. FIN, ACK, FIN
• B. ACK, FIN, ACK
• C. SYN, FIN, ACK
• D. FIN, ACK, FIN, ACK

Answer: (D)

Closing a TCP connection uses a four-way handshake with FIN and ACK. The process starts when one side wants to end its outgoing data: it sends a FIN to indicate it has finished sending. The other side replies with an ACK to confirm it received that FIN. When the peer is ready to close its side as well, it sends its own FIN. Finally, the original sender acknowledges that FIN with an ACK. This sequence—FIN, ACK, FIN, ACK—ensures both sides have completed their data transfer and can shut down cleanly.

Options that omit the final ACK, start with an unexpected ACK, or mix in a SYN (which is used to establish a connection) don’t fit the termination process.