This N10-009 practice question tests your understanding of network security. 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 network administrator reviews firewall logs and sees thousands of SYN packets coming from various source IP addresses to a single internal web server. No ACK or RST packets are observed from these sources. Which type of attack 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.
Why wrong: DNS amplification uses spoofed source IPs to send DNS queries that generate large responses to the victim; the logs would show DNS traffic, not SYN packets.
B
SYN flood attack
A SYN flood sends many SYN packets without completing the handshake, consuming server resources and causing denial of service.
C
ARP spoofing attack
Why wrong: ARP spoofing involves sending fake ARP replies; it would not generate SYN packets from many source IPs.
D
Man-in-the-middle attack
Why wrong: A man-in-the-middle attack intercepts and possibly modifies traffic; it does not typically involve a flood of SYN packets.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SYN flood attack
A SYN flood attack exploits the TCP three-way handshake by sending a high volume of SYN packets to a target server without completing the handshake (no ACK or RST). This exhausts the server's connection table resources, preventing legitimate connections. The observed pattern of many SYN packets from various sources with no subsequent ACK or RST is the hallmark of a SYN flood.
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.
✗
DNS amplification attack
Why it's wrong here
DNS amplification uses spoofed source IPs to send DNS queries that generate large responses to the victim; the logs would show DNS traffic, not SYN packets.
✓
SYN flood attack
Why this is correct
A SYN flood sends many SYN packets without completing the handshake, consuming server resources and causing denial of service.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
ARP spoofing attack
Why it's wrong here
ARP spoofing involves sending fake ARP replies; it would not generate SYN packets from many source IPs.
✗
Man-in-the-middle attack
Why it's wrong here
A man-in-the-middle attack intercepts and possibly modifies traffic; it does not typically involve a flood of SYN packets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between a SYN flood (which targets the TCP handshake) and a DNS amplification attack (which uses UDP reflection), so candidates may confuse the two because both involve high packet volumes and spoofed sources.
Trap categories for this question
Command / output trap
DNS amplification uses spoofed source IPs to send DNS queries that generate large responses to the victim; the logs would show DNS traffic, not SYN packets.
Detailed technical explanation
How to think about this question
In a SYN flood, the attacker sends SYN packets with spoofed source IP addresses, causing the server to allocate memory for half-open connections in its SYN backlog queue. Modern mitigations include SYN cookies (RFC 4987), which encode connection state in the SYN-ACK sequence number, allowing the server to avoid storing state until the handshake completes. Real-world SYN floods can overwhelm even large servers if not mitigated by rate limiting or dedicated DDoS protection appliances.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SYN flood attack — A SYN flood attack exploits the TCP three-way handshake by sending a high volume of SYN packets to a target server without completing the handshake (no ACK or RST). This exhausts the server's connection table resources, preventing legitimate connections. The observed pattern of many SYN packets from various sources with no subsequent ACK or RST is the hallmark of a SYN flood.
What should I do if I get this N10-009 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". 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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Question Discussion
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