Question 165 of 1,819

Switching and Network Access →mediumMultiple SelectObjective-mapped

Quick Answer

The correct answer is to configure dynamic ARP inspection (DAI) to prevent ARP spoofing, along with disabling unused ports, enabling PortFast with BPDU guard, and implementing DHCP snooping. These four measures form the core of switch port security best practices at Layer 2 because they address the most common attack vectors: DAI validates ARP packets against DHCP snooping bindings to block spoofing, while disabling unused ports in a shutdown state prevents unauthorized physical access and VLAN hopping. On the CCNA 200-301 v2 exam, this question tests your ability to distinguish between true security controls and ineffective measures like MAC filtering alone or changing the native VLAN to a higher number—a common trap is confusing native VLAN changes with actual security. Remember the mnemonic “DADP” for DAI, Admin-down ports, DHCP snooping, and PortFast with BPDU guard to lock down your Layer 2 defenses.

CCNA Switching and Network Access Practice Question

This 200-301 practice question tests your understanding of switching and network access. 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.

Which four of the following are considered best practices for securing switch ports and preventing Layer 2 attacks? (Choose all that apply. There are four correct answers.)

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1mediummulti select

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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

✓

Disable unused ports and place them in a shutdown state.

Disabling unused ports and placing them in a shutdown state (A) prevents unauthorized physical access and stops Layer 2 attacks like rogue device connections or VLAN hopping. Enabling PortFast and BPDU guard on ports connecting to end devices (B) speeds up STP convergence and protects against rogue switch loops. DHCP snooping (D) prevents rogue DHCP server attacks by filtering untrusted DHCP messages. Dynamic ARP inspection (E) uses DHCP snooping bindings to validate ARP packets and prevent ARP spoofing. Setting the native VLAN to a higher number (F) is not a best practice; the recommended approach is to change the native VLAN to an unused VLAN on both ends of the trunk and explicitly tag it. MAC address filtering as the sole measure (C) is easily bypassed and must be combined with port security or 802.1X.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that MAC address filtering is a strong standalone security measure, when in reality it is trivial to bypass and must be combined with other features like 802.1X or port security with sticky MAC addresses to be effective.

Detailed technical explanation

How to think about this question

DHCP snooping works by building a DHCP snooping binding table that maps client MAC addresses to IP addresses, VLANs, and port information, and it filters DHCP messages based on trusted and untrusted ports, effectively blocking rogue DHCP servers. Dynamic ARP inspection (DAI) uses this same binding table to validate ARP packets, dropping any that have a mismatch between the MAC and IP addresses, which prevents man-in-the-middle attacks via ARP spoofing. PortFast and BPDU guard work together on access ports: PortFast immediately transitions the port to forwarding state to speed up host connectivity, while BPDU guard shuts down the port if any BPDU is received, preventing accidental or malicious bridge loops from end devices.

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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 200-301 question test?

Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Disable unused ports and place them in a shutdown state. — Disabling unused ports and placing them in a shutdown state (A) prevents unauthorized physical access and stops Layer 2 attacks like rogue device connections or VLAN hopping. Enabling PortFast and BPDU guard on ports connecting to end devices (B) speeds up STP convergence and protects against rogue switch loops. DHCP snooping (D) prevents rogue DHCP server attacks by filtering untrusted DHCP messages. Dynamic ARP inspection (E) uses DHCP snooping bindings to validate ARP packets and prevent ARP spoofing. Setting the native VLAN to a higher number (F) is not a best practice; the recommended approach is to change the native VLAN to an unused VLAN on both ends of the trunk and explicitly tag it. MAC address filtering as the sole measure (C) is easily bypassed and must be combined with port security or 802.1X.

What should I do if I get this 200-301 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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