The correct choice is that an attacker is spoofing the client IP to send forged RST packets. This is because the TCP reset attack detection hinges on recognizing spoofed RST segments that arrive immediately after the SYN-ACK, before any data exchange, which forces the external server to abort the three-way handshake prematurely. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your ability to distinguish between a legitimate reset and a malicious spoofed RST attack, often appearing in IDS alert analysis questions. A common trap is assuming the internal host is compromised, but the key clue is the timing—the RSTs hit right after the SYN-ACK, not after data transfer, indicating the attacker is forging the source IP of 10.10.10.25 to disrupt connections. Memory tip: think "RST right after SYN-ACK equals spoofed attack."
200-201 Network Intrusion Analysis Practice Question
This 200-201 practice question tests your understanding of network intrusion analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security analyst is reviewing IDS alerts and notices multiple TCP resets sent from an internal host with IP 10.10.10.25 to various external IPs on port 443. The alerts indicate that these resets occur immediately after the corresponding SYN-ACK from the external server, before any data exchange. The analyst suspects a TCP reset attack. Which action is most likely occurring?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An attacker is spoofing the client IP to send forged RST packets.
The described behavior—TCP RST packets sent immediately after the SYN-ACK, before any data exchange, from an internal host to multiple external IPs on port 443—is characteristic of a TCP reset attack. In this attack, an adversary spoofs the source IP of the legitimate client (10.10.10.25) and sends forged RST segments to the external servers, causing them to abort the TCP handshake prematurely. This prevents the completion of the three-way handshake and disrupts the connection before any application data can be exchanged.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
A firewall is sending RST packets to block outbound traffic.
Why it's wrong here
A firewall would typically send RST with its own IP, not the client's IP.
✗
A client is properly closing a session after receiving data.
Why it's wrong here
Normal closure would occur after data exchange, not immediately after SYN-ACK.
✗
The client is retransmitting lost TCP segments.
Why it's wrong here
Retransmissions are data packets, not reset packets.
✓
An attacker is spoofing the client IP to send forged RST packets.
Why this is correct
This is a classic TCP reset attack where the attacker spoofs the client's IP to terminate a connection.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between a legitimate RST (sent by a host to abort a connection due to an error or policy) and a spoofed RST (sent by an attacker to disrupt a connection), and the trap here is that candidates may assume the RST is from a firewall or a normal closure without considering the timing and source IP spoofing.
Detailed technical explanation
How to think about this question
In a TCP reset attack, the attacker must guess or predict the correct sequence number to make the forged RST packet acceptable to the receiver. If the sequence number falls within the receiver's window, the connection is abruptly terminated. This attack is often mitigated by TCP timestamps (RFC 1323) or by using encrypted protocols like TLS, which make it harder for an off-path attacker to craft valid RST segments. In a real-world scenario, this could be part of a denial-of-service attempt against web servers, where the attacker aims to prevent legitimate clients from establishing HTTPS sessions.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An attacker is spoofing the client IP to send forged RST packets. — The described behavior—TCP RST packets sent immediately after the SYN-ACK, before any data exchange, from an internal host to multiple external IPs on port 443—is characteristic of a TCP reset attack. In this attack, an adversary spoofs the source IP of the legitimate client (10.10.10.25) and sends forged RST segments to the external servers, causing them to abort the TCP handshake prematurely. This prevents the completion of the three-way handshake and disrupts the connection before any application data can be exchanged.
What should I do if I get this 200-201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "immediately / without restart". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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