CCNA Network Services and Security Practice Question
Which switch security feature uses DHCP snooping bindings to validate ARP packets and help stop ARP spoofing?
⚠ Common exam trap
A common exam trap is selecting PortFast, UDLD, or HSRP preemption as the answer because these features are well-known switch security or stability mechanisms. However, PortFast only speeds up STP port transitions and does not inspect ARP packets. UDLD focuses on detecting unidirectional links and does not validate ARP traffic. HSRP preemption deals with gateway redundancy and has no role in ARP security. The key to avoiding this trap is recognizing that only Dynamic ARP Inspection uses DHCP snooping bindings to validate ARP packets and stop ARP spoofing.
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
✓
Dynamic ARP Inspection
Dynamic ARP Inspection compares ARP information to trusted bindings, often learned through DHCP snooping, to block forged ARP packets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
PortFast
Why it's wrong here
PortFast is a Spanning Tree Protocol (STP) feature that immediately transitions a switch port to the forwarding state to accommodate edge devices such as workstations or servers, bypassing the STP listening and learning delays. It does not inspect or validate ARP traffic and has no connection to DHCP snooping bindings, because its sole purpose is to accelerate network convergence for edge connectivity. Thus, PortFast is unrelated to the security function described in the question.
When this WOULD be correct
If the question asked about features that enhance the speed of port activation or reduce network downtime during link changes, PortFast would be the correct answer. For example, a question might ask which feature enables faster connectivity for end devices in a network.
- ✓
Dynamic ARP Inspection
Why this is correct
Dynamic ARP Inspection (DAI) validates ARP packets in a VLAN by cross-referencing the sender IP and MAC address against the DHCP snooping binding table, which is built from DHCP message exchanges. DAI intercepts all ARP requests and replies on untrusted interfaces and drops any packet whose IP-to-MAC mapping is not present or valid in that table. This direct reliance on DHCP snooping bindings is the precise mechanism that mitigates ARP spoofing, making DAI the correct answer.
- ✗
UDLD
Why it's wrong here
Unidirectional Link Detection (UDLD) is a Layer 2 protocol that detects anomalous conditions where a fiber link is transmitting frames in one direction but not receiving anything in return, typically due to misconfigured transceivers or physical faults. UDLD sends periodic protocol frames (similar to BPDUs) and eventually shuts down the interface to prevent routing loops, but it does not analyze ARP content or use DHCP snooping bindings. Therefore, UDLD addresses physical and data-link layer link integrity, not ARP spoofing.
When this WOULD be correct
If the question asked about a feature that detects and mitigates unidirectional links or loops in a network, such as 'Which feature helps identify unidirectional links to prevent network issues?', then UDLD would be the correct answer.
- ✗
HSRP preemption
Why it's wrong here
HSRP preemption is a feature in the Hot Standby Router Protocol that allows a standby router to become the active router when its configured priority is higher than that of the current active router, ensuring deterministic failover in a first-hop redundancy environment. This process operates at the IP routing layer and deals exclusively with forwarding of traffic to the default gateway, not with validating ARP frames. Since preemption depends on priority values and state transitions rather than DHCP snooping bindings, it is not the correct choice.
When this WOULD be correct
If the question asked about features related to router redundancy and failover mechanisms, specifically in the context of HSRP, then HSRP preemption would be the correct answer. For example, a question could ask which feature allows a backup router to regain active status when it becomes the highest priority router.
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 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Dynamic ARP InspectionCorrect answer▾
Why this is correct
Dynamic ARP Inspection (DAI) validates ARP packets in a VLAN by cross-referencing the sender IP and MAC address against the DHCP snooping binding table, which is built from DHCP message exchanges. DAI intercepts all ARP requests and replies on untrusted interfaces and drops any packet whose IP-to-MAC mapping is not present or valid in that table. This direct reliance on DHCP snooping bindings is the precise mechanism that mitigates ARP spoofing, making DAI the correct answer.
✗PortFastWrong answer — click to see why▾
Why this is wrong here
PortFast is a spanning-tree feature that immediately transitions a port to forwarding state, bypassing the listening and learning states. It does not inspect ARP packets or use DHCP snooping bindings, so it cannot prevent ARP spoofing.
★ When this WOULD be the correct answer
If the question asked about features that enhance the speed of port activation or reduce network downtime during link changes, PortFast would be the correct answer. For example, a question might ask which feature enables faster connectivity for end devices in a network.
Why candidates choose this
Students might confuse PortFast with security features because it is often enabled on access ports for faster connectivity, but its purpose is unrelated to ARP validation.
✗UDLDWrong answer — click to see why▾
Why this is wrong here
UDLD (Unidirectional Link Detection) is a protocol that detects and disables unidirectional links, which occur when traffic flows in one direction only. It does not inspect ARP packets or use DHCP snooping bindings, so it is not designed to stop ARP spoofing.
★ When this WOULD be the correct answer
If the question asked about a feature that detects and mitigates unidirectional links or loops in a network, such as 'Which feature helps identify unidirectional links to prevent network issues?', then UDLD would be the correct answer.
Why candidates choose this
UDLD sounds like a security feature because it detects link issues, but its focus is on physical layer problems, not ARP validation.
✗HSRP preemptionWrong answer — click to see why▾
Why this is wrong here
HSRP preemption is a feature of the Hot Standby Router Protocol that allows a higher-priority router to take over as the active router. It does not inspect ARP packets or use DHCP snooping bindings, so it cannot prevent ARP spoofing.
★ When this WOULD be the correct answer
If the question asked about features related to router redundancy and failover mechanisms, specifically in the context of HSRP, then HSRP preemption would be the correct answer. For example, a question could ask which feature allows a backup router to regain active status when it becomes the highest priority router.
Why candidates choose this
Students might associate HSRP with security because it provides redundancy, but preemption is about router role assignment, not ARP validation.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
RA Guard — IPv6 First-Hop Security
Key term
DHCP
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and network settings to devices on a network, so they can communicate without manual configuration.
Key term
DHCP snooping
DHCP snooping is a network security feature that filters untrusted DHCP messages to prevent rogue DHCP servers from giving out false IP addresses.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco 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 200-301 exam.