- 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.
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.
When this WOULD be correct
Dynamic ARP Inspection would be correct in a scenario where a rogue device is performing ARP spoofing or man-in-the-middle attacks by sending fake ARP replies, and the goal is to validate ARP packets against the DHCP snooping binding table.
- ✓
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.
When this WOULD be correct
Port security would be correct in a scenario where an attacker is performing MAC flooding or a CAM table overflow attack to intercept traffic, and the goal is to restrict the number of MAC addresses per port.
- ✗
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.
When this WOULD be correct
This option would be correct in a scenario where a legitimate DHCP server is being overwhelmed by excessive DHCP requests (e.g., due to a DoS attack), and the goal is to protect the server by limiting the rate of incoming DHCP packets.
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.
✓Change the port connecting the unauthorized server to an untrusted port.Correct answer▾
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.
✗Enable Dynamic ARP Inspection on the VLAN.Wrong answer — click to see why▾
Why this is wrong here
DHCP snooping already filters unauthorized DHCP servers by trusting only specific ports; Dynamic ARP Inspection (DAI) validates ARP packets, not DHCP offers, so it wouldn't stop the rogue DHCP server from assigning IP addresses.
★ When this WOULD be the correct answer
Dynamic ARP Inspection would be correct in a scenario where a rogue device is performing ARP spoofing or man-in-the-middle attacks by sending fake ARP replies, and the goal is to validate ARP packets against the DHCP snooping binding table.
Why candidates choose this
Candidates may confuse DHCP snooping with Dynamic ARP Inspection, thinking both are needed to fully secure DHCP, or they might believe DAI can block rogue DHCP servers since it relies on DHCP snooping bindings.
✗Configure port security on the unauthorized server's port to limit MAC addresses.Wrong answer — click to see why▾
Why this is wrong here
Port security limits the number of MAC addresses on a port but does not prevent a rogue DHCP server from offering addresses. The issue is DHCP snooping trust, not MAC flooding.
★ When this WOULD be the correct answer
Port security would be correct in a scenario where an attacker is performing MAC flooding or a CAM table overflow attack to intercept traffic, and the goal is to restrict the number of MAC addresses per port.
Why candidates choose this
Candidates may confuse port security with DHCP snooping, thinking that limiting MAC addresses can block unauthorized servers, but port security does not filter DHCP server messages.
✗Increase the rate limit on the unauthorized server's port.Wrong answer — click to see why▾
Why this is wrong here
Increasing the rate limit on the unauthorized server's port would allow more DHCP traffic, not block it. The issue is that the port is trusted, so DHCP snooping does not filter DHCP server messages from that port.
★ When this WOULD be the correct answer
This option would be correct in a scenario where a legitimate DHCP server is being overwhelmed by excessive DHCP requests (e.g., due to a DoS attack), and the goal is to protect the server by limiting the rate of incoming DHCP packets.
Why candidates choose this
Candidates may confuse rate limiting with security controls, thinking that limiting traffic can stop rogue servers, or they may misapply rate limiting as a general mitigation for unauthorized devices.
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?”
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.
Visual reference
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.
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Last reviewed: Jun 30, 2026
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