- A
Implement SYN cookies on the server.
SYN cookies encode connection information in the SYN-ACK response, enabling the server to remain stateless until the handshake completes. This prevents the connection table from filling up.
- B
Increase the server's TCP connection backlog.
Why wrong: Increasing the backlog provides more room for incomplete connections, but the server's resources are still finite. It is not a long-term mitigation for a large SYN flood.
- C
Enable bogon filtering on the perimeter firewall.
Why wrong: Bogon filtering blocks traffic from private or unallocated IP addresses. Attackers often use spoofed addresses, but this does not address the connection table exhaustion from a high volume of SYN packets.
- D
Deploy an intrusion prevention system (IPS) with signature detection.
Why wrong: An IPS can detect and block SYN floods, but it may not be as performant as server-side SYN cookies for handling high-rate attacks. SYN cookies are a more direct and often recommended mitigation.
N10-009 Network Security Practice Question
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 company's public web server is experiencing a flood of TCP SYN packets from multiple external IP addresses. The server's connection table is full, causing new legitimate connections to be dropped. Which of the following mitigation techniques should be implemented to protect the server while still allowing legitimate traffic?
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
Implement SYN cookies on the server.
SYN cookies allow the server to avoid storing connection state in the TCP backlog until the three-way handshake completes. When the SYN flood fills the connection table, the server encodes the initial sequence number (ISN) with cryptographic information about the connection, enabling it to verify the ACK from a legitimate client without consuming table entries. This technique preserves resources for legitimate traffic while dropping spoofed or incomplete handshakes.
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.
- ✓
Implement SYN cookies on the server.
Why this is correct
SYN cookies encode connection information in the SYN-ACK response, enabling the server to remain stateless until the handshake completes. This prevents the connection table from filling up.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the server's TCP connection backlog.
Why it's wrong here
Increasing the backlog provides more room for incomplete connections, but the server's resources are still finite. It is not a long-term mitigation for a large SYN flood.
When this WOULD be correct
This option would be correct in a scenario where the server is dropping legitimate connections due to a legitimate traffic spike (e.g., flash crowd) and the backlog is set too low, causing new connections to be rejected even though the server has capacity to handle them.
- ✗
Enable bogon filtering on the perimeter firewall.
Why it's wrong here
Bogon filtering blocks traffic from private or unallocated IP addresses. Attackers often use spoofed addresses, but this does not address the connection table exhaustion from a high volume of SYN packets.
- ✗
Deploy an intrusion prevention system (IPS) with signature detection.
Why it's wrong here
An IPS can detect and block SYN floods, but it may not be as performant as server-side SYN cookies for handling high-rate attacks. SYN cookies are a more direct and often recommended mitigation.
When this WOULD be correct
An IPS with signature detection would be correct for blocking application-layer attacks, such as SQL injection or cross-site scripting, where the attack payload is in the data stream and can be matched against signatures.
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.
✓Implement SYN cookies on the server.Correct answer▾
Why this is correct
SYN cookies encode connection information in the SYN-ACK response, enabling the server to remain stateless until the handshake completes. This prevents the connection table from filling up.
✗Increase the server's TCP connection backlog.Wrong answer — click to see why▾
Why this is wrong here
Increasing the TCP connection backlog only raises the limit of pending connections in the queue, but a SYN flood fills the connection table regardless of backlog size, so the server still exhausts resources and drops legitimate connections.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the server is dropping legitimate connections due to a legitimate traffic spike (e.g., flash crowd) and the backlog is set too low, causing new connections to be rejected even though the server has capacity to handle them.
Why candidates choose this
Candidates may think that a larger backlog can absorb more SYN packets, misunderstanding that SYN floods exhaust the connection table via half-open connections, not by exceeding the backlog limit.
✗Enable bogon filtering on the perimeter firewall.Wrong answer — click to see why▾
Why this is wrong here
Bogon filtering blocks traffic from invalid or unallocated IP addresses, but the SYN flood is coming from multiple external IPs that may be legitimate (spoofed or real). It does not prevent the connection table from filling up due to half-open connections.
★ When this WOULD be the correct answer
A company is receiving traffic from IP addresses that are known to be unallocated or reserved (e.g., private IPs on the internet). Enabling bogon filtering on the perimeter firewall would block this invalid traffic and protect the network.
Why candidates choose this
Candidates may think that blocking 'bad' IPs (bogons) is a general defense against any flood, but SYN floods often use spoofed or real distributed IPs that are not necessarily bogons.
✗Deploy an intrusion prevention system (IPS) with signature detection.Wrong answer — click to see why▾
Why this is wrong here
An IPS with signature detection can block known attack patterns, but it cannot prevent the connection table from filling up during a SYN flood because the attack traffic still reaches the server and consumes resources before the IPS can act.
★ When this WOULD be the correct answer
An IPS with signature detection would be correct for blocking application-layer attacks, such as SQL injection or cross-site scripting, where the attack payload is in the data stream and can be matched against signatures.
Why candidates choose this
Candidates may think an IPS can stop any type of attack, including SYN floods, because it is a general-purpose security device, but they overlook that SYN floods exploit TCP handshake mechanics that require endpoint-level mitigation.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The N10-009 exam often tests the misconception that increasing the TCP backlog (Option B) is a viable defense against SYN floods, but candidates must recognize that backlog tuning only delays exhaustion, whereas SYN cookies provide a stateless, scalable solution.
Detailed technical explanation
How to think about this question
SYN cookies are defined in RFC 4987 and work by encoding the MSS and a timestamp-based secret into the server's SYN-ACK sequence number. When the client responds with an ACK, the server reconstructs the connection without ever having stored a half-open entry. In high-rate floods, this stateless approach prevents the SYN backlog from filling, but it disables TCP options like window scaling and SACK, which can reduce throughput for legitimate connections.
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 N10-009 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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
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: Implement SYN cookies on the server. — SYN cookies allow the server to avoid storing connection state in the TCP backlog until the three-way handshake completes. When the SYN flood fills the connection table, the server encodes the initial sequence number (ISN) with cryptographic information about the connection, enabling it to verify the ACK from a legitimate client without consuming table entries. This technique preserves resources for legitimate traffic while dropping spoofed or incomplete handshakes.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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