- A
Enable Dynamic ARP Inspection on the VLAN.
Why wrong: Dynamic ARP Inspection validates ARP packets, not DHCP messages. It does not prevent a rogue DHCP server from offering addresses on a trusted port.
- B
Change the port connecting the unauthorized server to an untrusted port.
DHCP snooping treats trusted ports as authorized sources of DHCP offers. By making the port untrusted, the switch will drop any DHCP server messages received on that port.
- C
Configure port security on the unauthorized server's port to limit MAC addresses.
Why wrong: Port security restricts the number of MAC addresses on a port but does not filter DHCP messages. The rogue server could still issue DHCP offers.
- D
Increase the rate limit on the unauthorized server's port.
Why wrong: Rate limiting controls the amount of traffic, not the type of traffic. It would not prevent the rogue server from sending DHCP offers.
Quick Answer
The answer is to change the port connecting the unauthorized server to an untrusted port. This is correct because DHCP snooping enforces security by classifying switch ports as either trusted or untrusted; trusted ports are permitted to forward DHCP server messages like OFFER and ACK, while untrusted ports block them. Since the rogue server was connected to a trusted port, it could still hand out addresses, so reclassifying that port as untrusted forces the switch to drop all DHCP server traffic from that interface, effectively neutralizing the threat. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of DHCP snooping configuration and the common trap of misapplying trust settings—many candidates mistakenly think enabling snooping alone is enough, but the port-level trust assignment is the critical control. A helpful memory tip is "Trust the uplink, distrust the client": only ports connecting to legitimate DHCP servers (like the core switch or router) should ever be trusted; all client-facing ports must remain untrusted.
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has enabled DHCP snooping on all VLANs of the company's switches to mitigate the risk of rogue DHCP servers. After implementation, the analyst discovers that clients are still receiving IP addresses from an unauthorized DHCP server. The unauthorized server is connected to a switch port that is currently configured as a trusted port. What should the analyst do to stop the rogue DHCP server from offering addresses?
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
Change the port connecting the unauthorized server to an untrusted port.
DHCP snooping operates by designating switch ports as either trusted or untrusted. Trusted ports are allowed to send DHCP server messages (OFFER, ACK), while untrusted ports are blocked from sending such messages. Since the rogue server is connected to a trusted port, it can still offer IP addresses. Changing the port to untrusted will cause the switch to drop all DHCP server messages from that port, stopping the rogue server.
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.
- ✗
Enable Dynamic ARP Inspection on the VLAN.
Why it's wrong here
Dynamic ARP Inspection validates ARP packets, not DHCP messages. It does not prevent a rogue DHCP server from offering addresses on a trusted port.
- ✓
Change the port connecting the unauthorized server to an untrusted port.
Why this is correct
DHCP snooping treats trusted ports as authorized sources of DHCP offers. By making the port untrusted, the switch will drop any DHCP server messages received on that port.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Configure port security on the unauthorized server's port to limit MAC addresses.
Why it's wrong here
Port security restricts the number of MAC addresses on a port but does not filter DHCP messages. The rogue server could still issue DHCP offers.
- ✗
Increase the rate limit on the unauthorized server's port.
Why it's wrong here
Rate limiting controls the amount of traffic, not the type of traffic. It would not prevent the rogue server from sending DHCP offers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that DHCP snooping alone blocks all rogue servers, but the trap is that it only works if the rogue server's port is correctly classified as untrusted; candidates may forget that a trusted port bypasses all DHCP snooping filtering.
Detailed technical explanation
How to think about this question
DHCP snooping builds a DHCP snooping binding table by monitoring DHCPACK messages from trusted ports. When a DHCPOFFER arrives on an untrusted port, the switch drops it immediately, regardless of the source MAC or IP. In a real-world scenario, an attacker could connect a laptop running a DHCP server to an access port; if that port is mistakenly left as trusted, the attack succeeds. The fix is to ensure all access ports are untrusted by default and only uplinks to legitimate DHCP servers are trusted.
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.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
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: Change the port connecting the unauthorized server to an untrusted port. — DHCP snooping operates by designating switch ports as either trusted or untrusted. Trusted ports are allowed to send DHCP server messages (OFFER, ACK), while untrusted ports are blocked from sending such messages. Since the rogue server is connected to a trusted port, it can still offer IP addresses. Changing the port to untrusted will cause the switch to drop all DHCP server messages from that port, stopping the rogue server.
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 →
Same concept, more angles
1 more ways this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A security analyst notices that a network switch is receiving DHCP discover messages from a rogue device offering IP addresses. The rogue device is causing clients to obtain invalid IP addresses and lose network connectivity. Which security feature should be implemented on the switch to prevent this type of attack?
hard- A.Dynamic ARP inspection (DAI)
- ✓ B.DHCP snooping
- C.Port security
- D.802.1X authentication
Why B: B is correct because DHCP snooping is a security feature that filters untrusted DHCP messages on a switch. It distinguishes between trusted ports (connected to legitimate DHCP servers) and untrusted ports (connected to clients or rogue devices). When a rogue device sends DHCP discover messages offering IP addresses, DHCP snooping on untrusted ports drops those messages, preventing the rogue server from assigning invalid IP addresses.
Last reviewed: Jun 30, 2026
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.
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