N10-009 DAI inspects ARP packets on a switch. Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
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 enhances network access control by limiting the number of MAC addresses that can be learned on a switch port. It can be configured to statically assign MAC addresses or dynamically learn and "stick" them to a port, taking action like shutting down the port if the MAC address limit is exceeded. However, port security does not inspect the content of ARP packets or validate the IP-to-MAC address association within those packets, making it ineffective against an attacker who spoofs an existing, legitimate MAC address with a different IP.
When this WOULD be correct
Port security would be correct when the question asks how to prevent MAC flooding attacks or unauthorized devices from connecting by limiting the number of MAC addresses on a switch port.
- ✗
DHCP snooping
Why it's wrong here
DHCP snooping is primarily designed to prevent rogue DHCP servers from issuing IP addresses and to build a trusted database of IP-to-MAC address bindings. It inspects DHCP messages, allowing only trusted ports to respond to DHCP requests and dropping malformed or unauthorized DHCP traffic. While crucial for establishing the trust foundation that Dynamic ARP Inspection (DAI) relies upon, DHCP snooping itself does not directly validate ARP packets or prevent an attacker from sending forged ARP replies once an IP address is obtained.
- ✓
Dynamic ARP Inspection
Why this is correct
Dynamic ARP Inspection (DAI) directly mitigates ARP spoofing by validating ARP packets against a trusted database of IP-to-MAC address bindings. It intercepts all ARP requests and replies on untrusted ports, dropping any packets with invalid MAC-to-IP mappings or those that do not match entries learned from DHCP snooping. This proactive inspection ensures that only legitimate ARP traffic is forwarded, effectively preventing attackers from poisoning ARP caches and performing man-in-the-middle attacks.
- ✗
BPDU guard
Why it's wrong here
BPDU guard is a Spanning Tree Protocol (STP) feature designed to protect the integrity of the STP topology by disabling switch ports that unexpectedly receive Bridge Protocol Data Units (BPDUs). It is typically enabled on edge ports connected to end devices, preventing unauthorized switches from being introduced into the network and disrupting the STP calculation. This mechanism is entirely unrelated to the Address Resolution Protocol (ARP) or the validation of ARP messages, offering no defense against ARP spoofing attacks.
When this WOULD be correct
BPDU guard would be correct in a scenario where an unauthorized switch is connected to an access port, causing a spanning tree loop. The question would ask for a feature to protect against rogue switches sending BPDUs.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Dynamic ARP InspectionCorrect answer▾
Why this is correct
Dynamic ARP Inspection (DAI) directly mitigates ARP spoofing by validating ARP packets against a trusted database of IP-to-MAC address bindings. It intercepts all ARP requests and replies on untrusted ports, dropping any packets with invalid MAC-to-IP mappings or those that do not match entries learned from DHCP snooping. This proactive inspection ensures that only legitimate ARP traffic is forwarded, effectively preventing attackers from poisoning ARP caches and performing man-in-the-middle attacks.
✗Port securityWrong answer — click to see why▾
Why this is wrong here
Port security limits MAC addresses per port but does not inspect ARP packets, so it cannot prevent forged ARP replies that map the gateway IP to an attacker's MAC.
★ When this WOULD be the correct answer
Port security would be correct when the question asks how to prevent MAC flooding attacks or unauthorized devices from connecting by limiting the number of MAC addresses on a switch port.
Why candidates choose this
Candidates may think port security prevents all MAC-based attacks, confusing MAC address filtering with ARP inspection.
✗BPDU guardWrong answer — click to see why▾
Why this is wrong here
BPDU guard is used to prevent bridge loops by disabling ports that receive BPDUs, not to validate ARP packets or prevent ARP spoofing attacks.
★ When this WOULD be the correct answer
BPDU guard would be correct in a scenario where an unauthorized switch is connected to an access port, causing a spanning tree loop. The question would ask for a feature to protect against rogue switches sending BPDUs.
Why candidates choose this
Candidates may confuse BPDU guard with other security features like Dynamic ARP Inspection, or think it can prevent any type of spoofing attack due to its name containing 'guard'.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
Network Device Hardening
Key term
IP address
An IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
Key term
DHCP snooping
DHCP snooping is a network security feature that filters untrusted DHCP messages to prevent rogue DHCP servers from giving out false IP addresses.
About these practice questions
Courseiva writes every N10-009 question from scratch — 464 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.