N10-009 Network Security Practice Question
A network administrator discovers that client workstations are receiving IP addresses from an unknown device, causing network connectivity issues. Which security feature should be configured on switches to prevent rogue DHCP servers from assigning IP addresses?
⚠ Common exam trap
It's easy for candidates to confuse DHCP snooping with Dynamic ARP Inspection (DAI) because both rely on the DHCP snooping binding table, but DAI only validates ARP packets, not DHCP server messages.
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
✓
DHCP snooping
DHCP snooping is the correct security feature because it acts as a firewall between untrusted hosts and trusted DHCP servers. By configuring ports as trusted (where legitimate DHCP servers are connected) and untrusted (client-facing ports), the switch drops all DHCP server messages (OFFER, ACK, NAK) received on untrusted ports, effectively blocking rogue DHCP servers from assigning IP addresses.
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 is a Layer 2 security feature designed to prevent unauthorized DHCP servers from providing IP addresses and configuration to clients. It operates by classifying switch ports as either trusted, where legitimate DHCP server messages are allowed, or untrusted, where incoming DHCP server responses are blocked. This mechanism ensures that only approved DHCP servers can respond to client requests, effectively mitigating the risk of IP address conflicts and network misconfigurations caused by rogue devices.
- ✗
Dynamic ARP Inspection
Why it's wrong here
Dynamic ARP Inspection (DAI) is a security feature that validates ARP packets on a network, protecting against ARP spoofing and man-in-the-middle attacks. DAI inspects ARP requests and replies, dropping invalid packets based on information stored in the DHCP snooping binding table, which maps IP-to-MAC address bindings. Although it leverages DHCP snooping data for its validation process, DAI's primary function is to secure ARP traffic, not to prevent rogue DHCP servers from distributing IP addresses.
When this WOULD be correct
Dynamic ARP Inspection would be the correct answer in a scenario where a network administrator needs to prevent man-in-the-middle attacks caused by an attacker sending fake ARP replies to associate their MAC address with the IP address of a legitimate device (e.g., the default gateway).
- ✗
Port security
Why it's wrong here
Port security is a Layer 2 control mechanism that restricts the number of valid MAC addresses allowed on a specific switch port. It can be configured to learn MAC addresses dynamically, statically assign them, or use sticky MAC addresses, and then define an action if the configured limit is exceeded. While effective at preventing unauthorized devices from connecting or controlling MAC address flooding, it does not directly prevent a rogue DHCP server from responding to DHCP requests. A rogue DHCP server's activity is not primarily about exceeding MAC address limits but rather about distributing incorrect IP configuration.
When this WOULD be correct
Port security would be correct in a question about preventing unauthorized devices from connecting to the network by limiting the number of MAC addresses allowed on a port, e.g., 'A network administrator wants to prevent users from connecting personal switches to the network. Which feature should be enabled on switch ports?'
- ✗
BPDU guard
Why it's wrong here
BPDU guard is a Spanning Tree Protocol (STP) security feature designed to protect the integrity of the STP topology. It automatically disables a switch port if it receives a Bridge Protocol Data Unit (BPDU) from an unauthorized device, preventing rogue switches from manipulating the STP root bridge election or creating bridging loops. While crucial for network stability against misconfigured or malicious switches, it does not address the issue of unauthorized DHCP servers assigning IP addresses.
When this WOULD be correct
A network administrator wants to prevent unauthorized switches from being connected to access ports and causing spanning tree loops. BPDU guard would be the correct feature to configure on switch ports to disable them if a BPDU is received.
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.
✓DHCP snoopingCorrect answer▾
Why this is correct
DHCP snooping is a Layer 2 security feature designed to prevent unauthorized DHCP servers from providing IP addresses and configuration to clients. It operates by classifying switch ports as either trusted, where legitimate DHCP server messages are allowed, or untrusted, where incoming DHCP server responses are blocked. This mechanism ensures that only approved DHCP servers can respond to client requests, effectively mitigating the risk of IP address conflicts and network misconfigurations caused by rogue devices.
✗Dynamic ARP InspectionWrong answer — click to see why▾
Why this is wrong here
Dynamic ARP Inspection (DAI) is used to prevent ARP spoofing attacks by validating ARP packets, not to block rogue DHCP servers. The question specifically asks about preventing unauthorized DHCP server activity, which is addressed by DHCP snooping.
★ When this WOULD be the correct answer
Dynamic ARP Inspection would be the correct answer in a scenario where a network administrator needs to prevent man-in-the-middle attacks caused by an attacker sending fake ARP replies to associate their MAC address with the IP address of a legitimate device (e.g., the default gateway).
Why candidates choose this
Candidates may confuse DAI with DHCP snooping because both are security features that rely on a trusted database (DHCP snooping binding table) and are often implemented together. They might think DAI can also filter DHCP traffic, but its role is limited to ARP validation.
✗Port securityWrong answer — click to see why▾
Why this is wrong here
Port security limits the number of MAC addresses per switch port but does not inspect DHCP messages or block unauthorized DHCP servers. It cannot prevent rogue DHCP servers from assigning IP addresses.
★ When this WOULD be the correct answer
Port security would be correct in a question about preventing unauthorized devices from connecting to the network by limiting the number of MAC addresses allowed on a port, e.g., 'A network administrator wants to prevent users from connecting personal switches to the network. Which feature should be enabled on switch ports?'
Why candidates choose this
Candidates may confuse port security with DHCP snooping because both are switch security features, and they might think that restricting MAC addresses can block rogue DHCP servers, not realizing that DHCP snooping specifically validates DHCP messages.
✗BPDU guardWrong answer — click to see why▾
Why this is wrong here
BPDU guard is used to prevent loops by disabling ports that receive Bridge Protocol Data Units (BPDUs) from unauthorized switches, not to block rogue DHCP servers.
★ When this WOULD be the correct answer
A network administrator wants to prevent unauthorized switches from being connected to access ports and causing spanning tree loops. BPDU guard would be the correct feature to configure on switch ports to disable them if a BPDU is received.
Why candidates choose this
Candidates may confuse BPDU guard with DHCP snooping because both are security features that protect against unauthorized network devices, but they address different threats.
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?”
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Related to this question
Learn chapter
Network Device Hardening
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
Key term
DHCP server
A DHCP server is a network device or service that automatically assigns IP addresses and other network configuration parameters to devices on a network, eliminating the need for manual configuration.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.