The answer is DHCP snooping, the security feature that prevents rogue DHCP servers from distributing IP addresses by filtering untrusted DHCP messages on access switches. This works by designating all ports connected to end-user workstations as untrusted, which causes the switch to drop any DHCP server responses—such as OFFER and ACK packets—received on those ports. Only the authorized DHCP server in the server room, connected to a trusted port, is allowed to send these messages. On the CompTIA Network+ N10-009 exam, this question tests your understanding of Layer 2 security mechanisms, often appearing alongside ARP inspection or dynamic ARP inspection as a distractor. A common trap is confusing DHCP snooping with DHCP starvation attacks, but remember: snooping filters server replies, while starvation floods the server with fake requests. For a quick memory tip, think “snoop the server, starve the client”—DHCP snooping blocks unauthorized servers, not clients.
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 network administrator notices that several workstations on the network are receiving IP addresses from an unknown source, causing intermittent connectivity issues. The DHCP server is located in the server room and is the only authorized DHCP server. Which security feature should be implemented on the access switches to prevent rogue DHCP servers from distributing IP addresses?
DHCP Snooping filters DHCP messages and only allows DHCP offers from trusted ports, blocking rogue DHCP servers.
B
Dynamic ARP Inspection
Why wrong: DAI validates ARP packets to prevent ARP spoofing, not DHCP-related attacks.
C
IP Source Guard
Why wrong: IP Source Guard prevents IP spoofing by verifying source IP addresses against DHCP snooping bindings, but does not block rogue DHCP servers.
D
Port Security
Why wrong: Port Security restricts the number of MAC addresses per port, but does not prevent unauthorized DHCP servers.
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 security feature because it filters untrusted DHCP messages on access switches. By configuring ports connected to end-user workstations as untrusted, the switch drops DHCP server responses (OFFER, ACK) received on those ports, preventing rogue DHCP servers from distributing IP addresses. This ensures only the authorized DHCP server in the server room can provide IP configurations.
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.
✓
DHCP Snooping
Why this is correct
DHCP Snooping filters DHCP messages and only allows DHCP offers from trusted ports, blocking rogue DHCP servers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Dynamic ARP Inspection
Why it's wrong here
DAI validates ARP packets to prevent ARP spoofing, not DHCP-related attacks.
✗
IP Source Guard
Why it's wrong here
IP Source Guard prevents IP spoofing by verifying source IP addresses against DHCP snooping bindings, but does not block rogue DHCP servers.
✗
Port Security
Why it's wrong here
Port Security restricts the number of MAC addresses per port, but does not prevent unauthorized DHCP servers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between DHCP Snooping and Dynamic ARP Inspection, where candidates mistakenly choose DAI because they confuse DHCP spoofing with ARP spoofing, but DHCP Snooping is the specific mechanism to block rogue DHCP servers.
Detailed technical explanation
How to think about this question
DHCP Snooping operates by building a DHCP snooping binding table that maps client MAC addresses, IP addresses, VLAN, and port information. When a switch port is set to untrusted, the switch drops any DHCPOFFER, DHCPACK, or DHCPNAK messages received on that port, as these should only originate from the trusted uplink port connected to the authorized DHCP server. In a real-world scenario, a malicious user plugging a consumer router into an access port would be blocked from handing out IP addresses because the switch silently drops the DHCP server responses.
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 security feature because it filters untrusted DHCP messages on access switches. By configuring ports connected to end-user workstations as untrusted, the switch drops DHCP server responses (OFFER, ACK) received on those ports, preventing rogue DHCP servers from distributing IP addresses. This ensures only the authorized DHCP server in the server room can provide IP configurations.
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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