The answer is DHCP Snooping, the correct security feature to prevent rogue DHCP servers on a network. This works by filtering untrusted DHCP messages on a per-port basis, where the switch treats all ports as untrusted by default and only allows DHCP server responses like DHCPOFFER and DHCPACK from manually designated trusted ports, typically the uplink to the legitimate DHCP server. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of Layer 2 security mechanisms and often appears in scenario-based questions about unauthorized devices handing out IP addresses, with a common trap being confusion with Dynamic ARP Inspection, which validates ARP packets rather than DHCP messages. To remember the distinction, think of DHCP Snooping as the gatekeeper that silences any server trying to speak from an access port. A useful memory tip: "Trust the uplink, block the rest" — only the port facing your real DHCP server should ever be trusted.
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.
A network administrator is experiencing issues where unauthorized devices are offering IP addresses to clients, causing connectivity problems. Which security feature should be enabled on switches to prevent this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DHCP Snooping
C is correct because DHCP Snooping is a security feature that filters untrusted DHCP messages on a per-port basis, preventing unauthorized DHCP servers from offering IP addresses to clients. By configuring trusted ports (typically uplinks to legitimate DHCP servers) and untrusted ports (access ports), the switch drops DHCPOFFER and DHCPACK messages received on untrusted ports, directly stopping rogue DHCP server 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.
✗
Dynamic ARP Inspection (DAI)
Why it's wrong here
DAI protects against ARP spoofing, not rogue DHCP servers.
✗
IP Source Guard
Why it's wrong here
IP Source Guard prevents IP spoofing by filtering traffic based on DHCP snooping bindings, but does not directly block rogue DHCP servers.
✓
DHCP Snooping
Why this is correct
DHCP Snooping allows only DHCP messages from trusted DHCP servers, blocking unauthorized DHCP offers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Port Security
Why it's wrong here
Port Security limits the number of MAC addresses on a port but does not filter DHCP messages.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the roles of DHCP Snooping, DAI, and IP Source Guard, often selecting DAI because they associate ARP with address assignment, but only DHCP Snooping directly filters unauthorized DHCP server messages.
Detailed technical explanation
How to think about this question
DHCP Snooping builds a binding database (DHCP snooping binding table) that maps client MAC addresses, IP addresses, VLAN, and port information, which is then used by DAI and IP Source Guard for additional security. In a real-world scenario, an attacker could plug a consumer router into an access port; DHCP Snooping would drop its DHCPOFFER messages because the port is untrusted, while DAI alone would not catch this attack.
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 — C is correct because DHCP Snooping is a security feature that filters untrusted DHCP messages on a per-port basis, preventing unauthorized DHCP servers from offering IP addresses to clients. By configuring trusted ports (typically uplinks to legitimate DHCP servers) and untrusted ports (access ports), the switch drops DHCPOFFER and DHCPACK messages received on untrusted ports, directly stopping rogue DHCP server 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.
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 →
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 network administrator wants to prevent rogue DHCP servers from offering IP addresses to clients on the network. Which security feature should be enabled on the switches?
easy
✓ A.DHCP snooping
B.Dynamic ARP Inspection (DAI)
C.Port Security
D.IP Source Guard
Why A: DHCP snooping is the correct security feature because it acts as a firewall between untrusted hosts and trusted DHCP servers. It validates DHCP messages by filtering out responses from unauthorized DHCP servers on untrusted ports, preventing rogue servers from offering IP addresses to clients. This is achieved by building and maintaining a DHCP snooping binding database that tracks valid IP-to-MAC address mappings.
Variation 2. A network administrator wants to prevent unauthorized DHCP servers from offering IP addresses to clients on a switch. Which security feature should be enabled?
easy
A.BPDU guard
✓ B.DHCP snooping
C.Dynamic ARP inspection
D.Port security
Why B: DHCP snooping is the correct answer because it is a security feature specifically designed to filter untrusted DHCP messages on a switch. By configuring trusted and untrusted ports, DHCP snooping drops DHCP server responses (OFFER, ACK) received on untrusted ports, effectively preventing rogue DHCP servers from assigning IP addresses to clients.
Last reviewed: Jun 11, 2026
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