The answer is DHCP snooping. This security feature mitigates a DHCP starvation attack by filtering untrusted DHCP messages on access ports, where it rate-limits the number of DHCP discover packets and drops any DHCP server responses—such as OFFER or ACK—received on those ports, only allowing them on trusted uplink ports connected to the legitimate server. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of switch-based DHCP security; a common trap is confusing DHCP snooping with Dynamic ARP Inspection (DAI) or IP Source Guard, but remember that DHCP snooping directly prevents pool exhaustion by building a binding table of valid MAC-to-IP mappings and throttling spoofed discover floods. For a memory tip, think “Snooping stops the spoofing”—DHCP snooping snoops on the port to stop the starvation.
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.
An attacker is launching a DHCP starvation attack by sending a large number of DHCP discover messages with spoofed MAC addresses. This exhausts the DHCP pool and causes legitimate clients to fail to obtain IP addresses. Which security feature should be implemented on the switch to mitigate this attack?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DHCP snooping
DHCP snooping is the correct mitigation because it filters untrusted DHCP messages on access ports. By default, it only allows DHCP server responses (OFFER, ACK, etc.) on trusted ports (typically uplinks to the legitimate DHCP server) and drops them on untrusted ports, preventing a rogue or spoofed server from replying. Additionally, DHCP snooping builds a DHCP snooping binding table that tracks valid MAC-to-IP address mappings, which can be used to rate-limit DHCP discover messages and detect starvation attacks.
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 throttle DHCP requests or prevent DHCP starvation.
✓
DHCP snooping
Why this is correct
DHCP snooping includes rate limiting and filters DHCP messages on untrusted ports, effectively preventing DHCP starvation and rogue DHCP servers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Dynamic ARP Inspection (DAI)
Why it's wrong here
DAI validates ARP packets to prevent man-in-the-middle attacks but does not address DHCP starvation.
✗
802.1X
Why it's wrong here
802.1X provides network access control based on authentication, but it does not prevent DHCP starvation attacks.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests DHCP snooping as the answer for DHCP starvation attacks, but candidates confuse it with DAI because both rely on the DHCP snooping binding table, forgetting that DAI only validates ARP packets, not DHCP messages.
Detailed technical explanation
How to think about this question
DHCP snooping operates by classifying switch ports as trusted or untrusted; by default, all ports are untrusted. On untrusted ports, DHCP snooping drops all DHCP server messages (OFFER, ACK, NAK) and enforces a rate limit on DHCP client messages (DISCOVER, REQUEST, DECLINE, RELEASE) to prevent starvation. The DHCP snooping binding table also records the client MAC address, IP address, lease time, and port/VLAN, which can be used by DAI and IP Source Guard for additional security. In a real-world scenario, an attacker could use a tool like Yersinia to send thousands of DHCP discovers per second; without rate-limiting, the DHCP server's pool would be exhausted within seconds.
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 practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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: DHCP snooping — DHCP snooping is the correct mitigation because it filters untrusted DHCP messages on access ports. By default, it only allows DHCP server responses (OFFER, ACK, etc.) on trusted ports (typically uplinks to the legitimate DHCP server) and drops them on untrusted ports, preventing a rogue or spoofed server from replying. Additionally, DHCP snooping builds a DHCP snooping binding table that tracks valid MAC-to-IP address mappings, which can be used to rate-limit DHCP discover messages and detect starvation attacks.
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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Question Discussion
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