N10-009 DAI inspects ARP packets on a switch. 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. A key principle to apply: dAI inspects ARP packets on a switch.. 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 an unauthorized device is sending forged ARP replies, causing other devices to map the default gateway IP address to the attacker's MAC address. Which security feature should be implemented on the switches to prevent this attack?
Why wrong: Port security limits the number of MAC addresses per port but does not validate ARP packets.
B
DHCP snooping
Why wrong: DHCP snooping helps prevent rogue DHCP servers but is not the direct mitigation for ARP spoofing (though it is often used together with DAI).
C
Dynamic ARP Inspection
DAI specifically inspects ARP messages and blocks invalid ones, directly countering ARP spoofing.
D
BPDU guard
Why wrong: BPDU guard is used to prevent loops in spanning tree by disabling ports that receive BPDUs, unrelated to ARP security.
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 choice because it validates ARP packets on a per-port basis, ensuring that only legitimate ARP replies with correct IP-to-MAC bindings are forwarded. DAI uses a DHCP snooping binding table (or static ARP ACLs) to intercept and verify ARP packets, dropping forged replies that attempt to poison the ARP cache of other devices.
Key principle: DAI inspects ARP packets on a switch.
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 per port but does not validate ARP packets.
✗
DHCP snooping
Why it's wrong here
DHCP snooping helps prevent rogue DHCP servers but is not the direct mitigation for ARP spoofing (though it is often used together with DAI).
✓
Dynamic ARP Inspection
Why this is correct
DAI specifically inspects ARP messages and blocks invalid ones, directly countering ARP spoofing.
BPDU guard is used to prevent loops in spanning tree by disabling ports that receive BPDUs, unrelated to ARP security.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between DHCP snooping (which builds the binding table) and Dynamic ARP Inspection (which uses that table to filter ARP), 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 intercepting all ARP packets on untrusted ports and comparing the sender MAC and IP addresses against the DHCP snooping binding table; if no match is found, the packet is dropped. In environments without DHCP (e.g., static IPs), DAI can be configured with static ARP ACLs to define valid bindings. A subtle behavior is that DAI also validates ARP requests (gratuitous ARP) and can rate-limit ARP traffic to prevent DoS attacks on the switch CPU.
KKey Concepts to Remember
DAI inspects ARP packets on a switch.
DAI validates ARP packets against a trusted database (often built by DHCP snooping).
DAI drops invalid or forged ARP packets.
DAI prevents ARP spoofing/poisoning attacks.
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
DAI inspects ARP packets on a switch.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 — DAI inspects ARP packets on a switch..
What is the correct answer to this question?
The correct answer is: Dynamic ARP Inspection — Dynamic ARP Inspection (DAI) is the correct choice because it validates ARP packets on a per-port basis, ensuring that only legitimate ARP replies with correct IP-to-MAC bindings are forwarded. DAI uses a DHCP snooping binding table (or static ARP ACLs) to intercept and verify ARP packets, dropping forged replies that attempt to poison the ARP cache of other devices.
What should I do if I get this N10-009 question wrong?
Review dAI inspects ARP packets on a switch., then practise related N10-009 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
DAI inspects ARP packets on a switch.
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