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 security analyst discovers that users on the network are receiving ARP replies that map the default gateway IP address to an unknown MAC address. This is causing intermittent connectivity issues. Which type of attack is occurring, and what security feature should be implemented to prevent it?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ARP poisoning; Dynamic ARP Inspection (DAI)
This attack is ARP poisoning (also called ARP spoofing), where an attacker sends forged ARP replies to associate the default gateway's IP address with the attacker's MAC address. This allows the attacker to intercept, modify, or drop traffic intended for the gateway. Dynamic ARP Inspection (DAI) prevents this by validating ARP packets against a trusted DHCP snooping binding table, dropping any ARP reply that contains an IP-to-MAC mapping not present in the table.
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.
✗
MAC flooding; port security
Why it's wrong here
MAC flooding overwhelms the switch MAC table but does not involve forging ARP replies.
✓
ARP poisoning; Dynamic ARP Inspection (DAI)
Why this is correct
DAI trusts only ARP responses that match a valid IP-to-MAC binding, preventing ARP spoofing.
Related concept
Read the scenario before looking for a memorised answer.
✗
DHCP starvation; DHCP snooping
Why it's wrong here
DHCP starvation exhausts the DHCP server's address pool; DHCP snooping prevents rogue DHCP servers, not ARP attacks.
✗
DNS poisoning; DNSSEC
Why it's wrong here
DNS poisoning targets the DNS cache, not ARP messages.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between Layer 2 attacks (ARP poisoning, MAC flooding) and Layer 3/4 attacks (DHCP starvation, DNS poisoning), so candidates mistakenly choose DHCP starvation or DNS poisoning because they involve 'spoofing' or 'poisoning' without recognizing that the symptom—ARP replies mapping the gateway IP to an unknown MAC—is a direct indicator of ARP manipulation.
Detailed technical explanation
How to think about this question
ARP poisoning exploits the stateless nature of ARP—hosts accept unsolicited ARP replies (gratuitous ARPs) without verification. DAI relies on DHCP snooping to build a binding table of legitimate IP-MAC pairs; on untrusted ports, DAI intercepts all ARP packets and compares the sender MAC and IP against this table, dropping any mismatch. In a real-world scenario, an attacker on a guest VLAN could poison the default gateway ARP cache of all clients, performing a man-in-the-middle attack to capture credentials before forwarding traffic to the real gateway.
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.
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: ARP poisoning; Dynamic ARP Inspection (DAI) — This attack is ARP poisoning (also called ARP spoofing), where an attacker sends forged ARP replies to associate the default gateway's IP address with the attacker's MAC address. This allows the attacker to intercept, modify, or drop traffic intended for the gateway. Dynamic ARP Inspection (DAI) prevents this by validating ARP packets against a trusted DHCP snooping binding table, dropping any ARP reply that contains an IP-to-MAC mapping not present in the table.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.