Describe the TCP four-way termination handshake and what each step accomplishes.

• A. One side sends FIN to close its send channel; the other side ACKs; the other side then sends FIN; the first side ACKs to complete the close.
• B. SYN is used to close the connection.
• C. FIN is sent by both sides at the same time.
• D. ACK closes the connection automatically without any FIN.

Answer: (A)

Closing a TCP connection is a coordinated four-step process that lets both sides finish sending data and confirms the shutdown has been received. It starts with one side sending a FIN, signaling it has no more data to transmit. The other side responds with an ACK to acknowledge that FIN, while still potentially sending data in the opposite direction. When that peer is ready to finish its own transmission, it sends its own FIN. The original sender then replies with a final ACK, completing the close. This back-and-forth ensures both sides agree on the shutdown, allows any in-flight data to be acknowledged, and typically places the initiator into a short TIME_WAIT period to guard against late-arriving packets.