N10-009 Networking Concepts Practice Question
A client and server are establishing a TCP connection. The client sends a SYN segment to the server. The server responds with a SYN-ACK segment. What is the next segment in the handshake?
⚠ Common exam trap
The N10-009 exam often tests the misconception that the handshake ends after the SYN-ACK, or that a FIN or RST could be used to complete the handshake, when in fact the final ACK is mandatory to transition the server's state from SYN-RECEIVED to ESTABLISHED.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ACK
The TCP three-way handshake requires the client to acknowledge the server's SYN-ACK by sending an ACK segment. This completes the handshake, establishing a full-duplex connection with synchronized sequence numbers. Without this final ACK, the server remains in a half-open state, unable to begin data transmission.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ACK
Why this is correct
This is the third and final step of the TCP three-way handshake. After the client sends a SYN and the server responds with a SYN-ACK, the client must send an ACK segment. This final acknowledgment confirms the server's SYN-ACK, successfully establishing a full-duplex connection and making it ready for reliable data transfer. The ACK segment carries no data but signifies the completion of the connection setup.
- ✗
RST
Why it's wrong here
A TCP RST (Reset) flag is used to immediately terminate a TCP connection, often due to an error, an unresponsive port, or an attempt to connect to a non-existent service. It signifies an abrupt closure, discarding any buffered data and not following the graceful shutdown procedure. Sending an RST during the handshake would prevent connection establishment, indicating a rejection rather than completion.
When this WOULD be correct
A question asks: 'After a client sends a SYN to a closed port, the server responds with an RST. What is the next segment?' In that case, the server sends RST, not SYN-ACK, and the client does not send anything further.
- ✗
FIN
Why it's wrong here
The TCP FIN (Finish) flag is part of the four-way handshake used to gracefully close an established TCP connection. When a host is ready to stop sending data, it sends a FIN segment to its peer. This allows both sides to acknowledge the end of data transmission independently, ensuring all buffered data is delivered before the connection is fully terminated. It plays no role in the initial connection establishment phase.
When this WOULD be correct
In a question about TCP connection termination, after the server sends a FIN segment, the client would respond with an ACK (or the server might send FIN after receiving a FIN from the client).
- ✗
SYN
Why it's wrong here
The TCP SYN (Synchronize) flag is used by the client to initiate a connection, proposing initial sequence numbers. In the context of a client and server establishing a connection, the client sends the *first* SYN. Sending a *second* SYN after receiving a SYN-ACK from the server would restart the handshake process entirely, indicating that the client did not properly receive or acknowledge the server's response, rather than completing the ongoing establishment.
When this WOULD be correct
A question asking about the first step of the TCP handshake: 'What does a client send to initiate a connection?' would have SYN as the correct answer.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓ACKCorrect answer▾
Why this is correct
This is the third and final step of the TCP three-way handshake. After the client sends a SYN and the server responds with a SYN-ACK, the client must send an ACK segment. This final acknowledgment confirms the server's SYN-ACK, successfully establishing a full-duplex connection and making it ready for reliable data transfer. The ACK segment carries no data but signifies the completion of the connection setup.
✗RSTWrong answer — click to see why▾
Why this is wrong here
In a TCP three-way handshake, after the server sends SYN-ACK, the client must send an ACK to complete the connection. RST is used to reset a connection, not to continue the handshake.
★ When this WOULD be the correct answer
A question asks: 'After a client sends a SYN to a closed port, the server responds with an RST. What is the next segment?' In that case, the server sends RST, not SYN-ACK, and the client does not send anything further.
Why candidates choose this
Candidates may confuse RST with ACK or think that a reset is part of the normal handshake, especially if they recall that RST can be used to reject a connection attempt.
✗FINWrong answer — click to see why▾
Why this is wrong here
The TCP three-way handshake requires an ACK from the client after receiving SYN-ACK; FIN is used to terminate a connection, not to establish it.
★ When this WOULD be the correct answer
In a question about TCP connection termination, after the server sends a FIN segment, the client would respond with an ACK (or the server might send FIN after receiving a FIN from the client).
Why candidates choose this
Candidates may confuse the connection establishment handshake with the termination handshake, where FIN is a key segment.
✗SYNWrong answer — click to see why▾
Why this is wrong here
In the TCP three-way handshake, after the server sends SYN-ACK, the client must send an ACK to complete the connection. Sending a SYN again would be redundant and violate the handshake sequence.
★ When this WOULD be the correct answer
A question asking about the first step of the TCP handshake: 'What does a client send to initiate a connection?' would have SYN as the correct answer.
Why candidates choose this
Candidates may confuse the handshake steps or think that the client needs to send another SYN to confirm, not realizing that the SYN-ACK already acknowledges the client's SYN.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Related to this question
Learn chapter
Spanning Tree Protocol Concepts
Key term
Segment
A segment is a division of a larger network, such as a collision domain, broadcast domain, or a portion of a TCP data stream, used to organize traffic and improve performance.
Key term
TCP
TCP (Transmission Control Protocol) is a core internet protocol that ensures data is sent reliably and in order between devices over a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.