- A
The DHCP pool is not associated with the correct VLAN interface using the network command.
Correct because if the network command in the DHCP pool does not match the subnet of the VLAN, the DHCP server may assign addresses but not apply the pool-specific options like DNS.
- B
The DNS server is unreachable from the DHCP server.
Why wrong: Incorrect because the DHCP server does not need to reach the DNS server to include its address in the DHCP offer; it only needs to provide the IP.
- C
The ip dhcp excluded-address command is blocking the DNS server IP.
Why wrong: Incorrect because the excluded-address command prevents the DHCP server from assigning an IP address; it does not affect option delivery.
- D
The DHCP client is configured with a static DNS server address.
Why wrong: Incorrect because if the client had a static DNS, it would ignore the DHCP option, but the scenario implies the client is using DHCP for all settings.
Quick Answer
The answer is that the DHCP pool is not associated with the correct VLAN interface using the network command. Even though the dns-server command is correctly configured, the router’s DHCP server binds address pools to specific subnets via the network statement, and if that statement does not match the subnet of the VLAN interface receiving client requests, the server will assign addresses from a default or mismatched pool—ignoring the intended DNS configuration. On the ENCOR 350-401 exam, this scenario tests your understanding of how Cisco IOS DHCP server logic selects pools based on the incoming interface’s IP subnet, not just the pool name or DNS settings. A common trap is to focus on relay agents or missing options, but the root cause is often a missing or incorrect network command. Memory tip: “Pool picks by network, not by name—match the interface subnet or clients play a different game.”
CCNP NAT and DHCP Practice Question
This 350-401 practice question tests your understanding of nat and dhcp. 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.
A network engineer is troubleshooting a DHCP issue on a Cisco router configured as a DHCP server for a VLAN. Clients in the VLAN are able to obtain IP addresses from the DHCP server, but they are not receiving the correct DNS server address. The engineer checks the DHCP pool configuration and sees the dns-server command is configured with the correct IP address. What is the most likely cause of the problem?
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
The DHCP pool is not associated with the correct VLAN interface using the network command.
The DHCP server configuration appears correct, but the clients are not receiving the DNS server address. This often happens when the DHCP server is not the default gateway and DHCP relay is involved, or when the DHCP pool is not bound to the correct interface.
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 pool is not associated with the correct VLAN interface using the network command.
Why this is correct
Correct because if the network command in the DHCP pool does not match the subnet of the VLAN, the DHCP server may assign addresses but not apply the pool-specific options like DNS.
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 DNS server is unreachable from the DHCP server.
- ✗
The ip dhcp excluded-address command is blocking the DNS server IP.
Why it's wrong here
Incorrect because the excluded-address command prevents the DHCP server from assigning an IP address; it does not affect option delivery.
- ✗
The DHCP client is configured with a static DNS server address.
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
Command / output trap
Incorrect because the excluded-address command prevents the DHCP server from assigning an IP address; it does not affect option delivery.
Scenario analysis trap
Incorrect because if the client had a static DNS, it would ignore the DHCP option, but the scenario implies the client is using DHCP for all settings.
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 350-401 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 350-401 question test?
NAT and DHCP — This question tests NAT and DHCP — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The DHCP pool is not associated with the correct VLAN interface using the network command. — The DHCP server configuration appears correct, but the clients are not receiving the DNS server address. This often happens when the DHCP server is not the default gateway and DHCP relay is involved, or when the DHCP pool is not bound to the correct interface.
What should I do if I get this 350-401 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 350-401 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 18, 2026
This 350-401 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 350-401 exam.
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