The answer is Dynamic ARP Inspection (DAI). This security feature prevents an attacker from sending forged ARP messages to redirect traffic by validating every ARP packet against a trusted database, typically the DHCP snooping binding table, which contains legitimate MAC-to-IP address mappings. On the CompTIA Network+ N10-009 exam, DAI is tested as a Layer 2 security mechanism that operates on untrusted switch ports, intercepting and verifying ARP requests and replies to block ARP spoofing attacks. A common trap is confusing DAI with DHCP snooping; remember that DHCP snooping builds the trusted binding table, while DAI enforces it. For a memory tip, think of DAI as the “bouncer” checking IDs at the door—if the MAC-to-IP pair isn’t on the guest list, the ARP message gets denied entry.
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.
Which security feature on a switch can prevent an attacker from sending forged ARP messages to redirect traffic?
Why wrong: Port security limits the number of MAC addresses on a port, but does not validate ARP messages.
B
DHCP snooping
Why wrong: DHCP snooping filters DHCP messages and builds a binding table, but does not inspect ARP packets directly. However, DAI relies on DHCP snooping.
C
Dynamic ARP Inspection
DAI uses the DHCP snooping binding table to validate ARP packets and drop invalid ones, preventing ARP spoofing.
D
VLAN segmentation
Why wrong: VLAN segmentation limits broadcast domains but does not prevent ARP spoofing within the same VLAN.
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 against a trusted database (the DHCP snooping binding table) to ensure that the MAC-to-IP address mapping is legitimate. By intercepting and verifying all ARP requests and replies on untrusted ports, DAI prevents an attacker from sending forged ARP messages to redirect traffic (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 limits the number of MAC addresses on a port, but does not validate ARP messages.
✗
DHCP snooping
Why it's wrong here
DHCP snooping filters DHCP messages and builds a binding table, but does not inspect ARP packets directly. However, DAI relies on DHCP snooping.
✓
Dynamic ARP Inspection
Why this is correct
DAI uses the DHCP snooping binding table to validate ARP packets and drop invalid ones, preventing ARP spoofing.
Related concept
Read the scenario before looking for a memorised answer.
✗
VLAN segmentation
Why it's wrong here
VLAN segmentation limits broadcast domains but does not prevent ARP spoofing within the same VLAN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between DHCP snooping (which builds the trust database) and Dynamic ARP Inspection (which uses that database to validate ARP traffic), leading candidates to mistakenly choose DHCP snooping as the direct defense against ARP spoofing.
Detailed technical explanation
How to think about this question
DAI operates by comparing the sender MAC and sender IP in each ARP packet against entries in the DHCP snooping binding table; if no match is found, the packet is dropped. It also enforces rate limiting on ARP packets to prevent ARP flooding attacks. In a real-world scenario, an attacker on an untrusted port could send a gratuitous ARP claiming the gateway's IP, but DAI would drop it because the MAC address does not match the binding table entry.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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 against a trusted database (the DHCP snooping binding table) to ensure that the MAC-to-IP address mapping is legitimate. By intercepting and verifying all ARP requests and replies on untrusted ports, DAI prevents an attacker from sending forged ARP messages to redirect traffic (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.
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