- A
The DHCP snooping binding table is exhausted and cannot accept new bindings for the static hosts.
Why wrong: Static hosts do not attempt to obtain a DHCP address and thus never generate DHCP bindings. They do not consume entries in the DHCP snooping binding table, so exhaustion is not the cause.
- B
IP Source Guard is also enabled on VLAN 20 and is blocking traffic from hosts that have no DHCP snooping binding.
Why wrong: IP Source Guard relies on the DHCP snooping binding table to filter IP traffic, but the symptom is ARP resolution failure after DAI was enabled. While IP Source Guard could block traffic if enabled, it is not mentioned and DAI alone explains the observed drop of ARP packets.
- C
DAI is dropping ARP packets from the static hosts because they do not have a corresponding entry in the DHCP snooping binding table.
When DAI is enabled, it checks every ARP packet on untrusted ports against the DHCP snooping binding table. Since the static hosts have no DHCP lease, no binding exists, and DAI drops their ARP packets, preventing them from learning the gateway MAC address and causing loss of connectivity.
- D
The switch is detecting ARP spoofing from the static hosts and has shut down their switchport interfaces for security.
Why wrong: By default, DAI does not shut down interfaces; it simply drops invalid ARP packets. While ARP rate-limiting can cause a port to be err-disabled, that is not the default behavior, and the scenario does not mention interface status changes, only connectivity loss.
Quick Answer
The answer is that Dynamic ARP Inspection is dropping ARP packets from the static hosts because they lack a corresponding entry in the DHCP snooping binding table. DAI validates every ARP packet on a trusted VLAN by cross-referencing the sender’s IP and MAC against this binding table, which is built exclusively from DHCP lease information. Since statically configured hosts never generate a DHCP binding, DAI treats their ARP replies as invalid and silently drops them, breaking the ARP resolution needed to reach the default gateway. On the CCNA 200-301 v2 exam, this scenario tests your understanding that DAI and DHCP snooping are tightly coupled; a common trap is assuming static hosts work fine if their IP and MAC are correct. Remember the key dependency: no DHCP binding means no DAI validation. A useful memory tip is “Static = No Binding = No ARP,” so always configure a static DAI ACL or a trusted port for non-DHCP hosts.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
After enabling Dynamic ARP Inspection on VLAN 20, a network engineer notices that some hosts lose connectivity. The affected hosts have correct IP addresses and MAC addresses, but they cannot ping the default gateway. All other hosts on the same VLAN work fine. Further investigation reveals that the non-functioning hosts are using static IP configurations, while the working hosts are DHCP clients. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
DAI is dropping ARP packets from the static hosts because they do not have a corresponding entry in the DHCP snooping binding table.
Dynamic ARP Inspection (DAI) uses the DHCP snooping binding table to validate ARP packets. Hosts with statically assigned IP addresses have no DHCP binding entry, so DAI considers their ARP packets invalid and drops them, preventing these hosts from resolving MAC addresses and thus causing loss of connectivity.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The DHCP snooping binding table is exhausted and cannot accept new bindings for the static hosts.
Why it's wrong here
Static hosts do not attempt to obtain a DHCP address and thus never generate DHCP bindings. They do not consume entries in the DHCP snooping binding table, so exhaustion is not the cause.
- ✗
IP Source Guard is also enabled on VLAN 20 and is blocking traffic from hosts that have no DHCP snooping binding.
Why it's wrong here
IP Source Guard relies on the DHCP snooping binding table to filter IP traffic, but the symptom is ARP resolution failure after DAI was enabled. While IP Source Guard could block traffic if enabled, it is not mentioned and DAI alone explains the observed drop of ARP packets.
- ✓
DAI is dropping ARP packets from the static hosts because they do not have a corresponding entry in the DHCP snooping binding table.
Why this is correct
When DAI is enabled, it checks every ARP packet on untrusted ports against the DHCP snooping binding table. Since the static hosts have no DHCP lease, no binding exists, and DAI drops their ARP packets, preventing them from learning the gateway MAC address and causing loss of connectivity.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The switch is detecting ARP spoofing from the static hosts and has shut down their switchport interfaces for security.
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.
✓DAI is dropping ARP packets from the static hosts because they do not have a corresponding entry in the DHCP snooping binding table.Correct answer▾
Why this is correct
When DAI is enabled, it checks every ARP packet on untrusted ports against the DHCP snooping binding table. Since the static hosts have no DHCP lease, no binding exists, and DAI drops their ARP packets, preventing them from learning the gateway MAC address and causing loss of connectivity.
✗The DHCP snooping binding table is exhausted and cannot accept new bindings for the static hosts.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think that a large number of untrusted hosts could overwhelm the binding table, but static hosts do not interact with DHCP and would not fill the table or be rejected.
✗IP Source Guard is also enabled on VLAN 20 and is blocking traffic from hosts that have no DHCP snooping binding.Wrong answer — click to see why▾
Why this is wrong here
Candidates often confuse DAI and IP Source Guard since both use DHCP snooping; however, DAI specifically validates ARP packets, which matches the symptom of connectivity loss due to ARP resolution failure.
✗The switch is detecting ARP spoofing from the static hosts and has shut down their switchport interfaces for security.Wrong answer — click to see why▾
Why this is wrong here
Some candidates might associate ARP security features with port shutdown, but standard DAI operation does not disable ports, and the symptom does not indicate interface down events.
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?”
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Scenario analysis trap
By default, DAI does not shut down interfaces; it simply drops invalid ARP packets. While ARP rate-limiting can cause a port to be err-disabled, that is not the default behavior, and the scenario does not mention interface status changes, only connectivity loss.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: DAI is dropping ARP packets from the static hosts because they do not have a corresponding entry in the DHCP snooping binding table. — Dynamic ARP Inspection (DAI) uses the DHCP snooping binding table to validate ARP packets. Hosts with statically assigned IP addresses have no DHCP binding entry, so DAI considers their ARP packets invalid and drops them, preventing these hosts from resolving MAC addresses and thus causing loss of connectivity.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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Last reviewed: Jun 14, 2026
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