Dynamic ARP Inspection (DAI) is the correct choice because it actively validates ARP packets against a trusted binding table built by DHCP snooping, dropping any spoofed replies that attempt to associate an attacker’s MAC address with a legitimate host’s IP. This directly prevents man-in-the-middle attacks on a switched network by ensuring only authorized ARP responses are forwarded. On the CompTIA Network+ N10-009 exam, this scenario often appears as a high-volume ARP request alert, testing your ability to distinguish DAI from other mitigations like port security or MAC filtering—both of which fail to inspect ARP content. A common trap is choosing "static ARP entries," but DAI dynamically enforces trust. Memory tip: DAI = "Drop ARP Imposters" by checking the DHCP snooping database.
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 receives an alert that an internal user's workstation is sending a high volume of ARP requests for multiple IP addresses on the local subnet. The analyst suspects a man-in-the-middle attack. Which security mechanism is most effective at mitigating this type of attack on a switched network?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Dynamic ARP Inspection
Dynamic ARP Inspection (DAI) is the correct answer because it validates ARP packets on a switched network, ensuring that only legitimate ARP replies are forwarded. In a man-in-the-middle attack, an attacker sends spoofed ARP replies to associate their MAC address with the IP address of a legitimate host. DAI intercepts all ARP packets and compares them against a trusted binding table (built by DHCP snooping), dropping any that are invalid, thus preventing ARP spoofing.
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.
✗
Port security
Why it's wrong here
Port security restricts the number of MAC addresses per port but does not inspect ARP packets.
✗
DHCP snooping
Why it's wrong here
DHCP snooping filters rogue DHCP servers and builds a binding table, but does not directly validate ARP traffic.
✓
Dynamic ARP Inspection
Why this is correct
DAI uses the DHCP snooping binding table to validate ARP packets and block spoofed ARP messages.
Related concept
Read the scenario before looking for a memorised answer.
✗
MAC address filtering
Why it's wrong here
MAC filtering controls which MAC addresses are allowed, but does not prevent ARP spoofing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between DHCP snooping and DAI, where candidates mistakenly choose DHCP snooping because it builds the binding table, but DAI is the actual mechanism that validates ARP packets to prevent man-in-the-middle attacks.
Detailed technical explanation
How to think about this question
DAI operates by intercepting all ARP requests and replies on untrusted ports and verifying each packet's sender MAC and sender IP against the DHCP snooping binding table. If no entry exists or the information mismatches, the packet is dropped. In a real-world scenario, an attacker could use a tool like arpspoof to send gratuitous ARP replies; DAI would drop these because the attacker's MAC is not bound to the target IP in the binding table. DAI also supports rate limiting to prevent ARP flooding attacks.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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: Dynamic ARP Inspection — Dynamic ARP Inspection (DAI) is the correct answer because it validates ARP packets on a switched network, ensuring that only legitimate ARP replies are forwarded. In a man-in-the-middle attack, an attacker sends spoofed ARP replies to associate their MAC address with the IP address of a legitimate host. DAI intercepts all ARP packets and compares them against a trusted binding table (built by DHCP snooping), dropping any that are invalid, thus preventing ARP spoofing.
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
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Variation 1. A security analyst detects that an attacker is sending forged ARP replies to associate the attacker's MAC address with the IP address of the default gateway. What is this attack called?
hard
✓ A.ARP poisoning
B.MAC flooding
C.DHCP snooping
D.DNS spoofing
Why A: ARP poisoning (also known as ARP spoofing) is the correct answer because the attacker sends forged ARP replies to associate their MAC address with the IP address of the default gateway. This causes the victim's switch to update its ARP cache with the attacker's MAC for the gateway's IP, enabling man-in-the-middle attacks where the attacker intercepts traffic destined for the gateway.
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Question Discussion
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