101 · Question #595

101 Question #595: Real Exam Question with Answer & Explanation

The correct answer is D: send an ACK Packet. In TCP's four-way connection termination, receiving a FIN triggers an ACK - not a reset or new connection initiation.

Question

A client receives all of the expected data from a server and sends a FIN packet signaling the end of communication. What will the server do when it receives the FIN Packet from the client?

Options

Asend a SYN packet
Bsend an RST packet
CSend both FIN and RST packets
Dsend an ACK Packet

Explanation

In TCP's four-way connection termination, receiving a FIN triggers an ACK - not a reset or new connection initiation.

Common mistakes.

A. SYN packets initiate new TCP connections and have no role in connection termination.
B. RST packets abruptly terminate a connection due to an error condition, not as a normal graceful response to a FIN.
C. Sending both FIN and RST simultaneously is not standard TCP behavior; the FIN and ACK are sent in separate steps of the termination sequence.

Concept tested. TCP four-way connection termination sequence

Reference. https://datatracker.ietf.org/doc/html/rfc793

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