- 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.
Quick Answer
The answer is to implement SYN cookies on the server. This technique mitigates a SYN flood by encoding connection details into the initial sequence number (ISN) sent in the SYN-ACK, allowing the server to avoid storing any state in its connection table until the three-way handshake completes. When the table is full from spoofed or incomplete handshakes, SYN cookies let the server cryptographically verify a legitimate client’s ACK without consuming a backlog entry, preserving resources for real traffic. On the CompTIA Network+ N10-009 exam, this tests your understanding of TCP handshake mechanics and resource exhaustion attacks; a common trap is confusing SYN cookies with rate limiting or firewalls, which block traffic rather than offload state. Remember the memory tip: “Cookies are baked after the ACK, not before the SYN,” meaning the server only commits memory once the client proves it’s real.
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.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco 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 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.
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
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.
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