- A
The WLC does not have a CAPWAP source interface configured.
Correct because the CAPWAP source interface must be configured on the WLC so that APs can discover and communicate with it. Without it, the WLC may not respond to CAPWAP discovery requests.
- B
The APs are not configured with DHCP option 43 to point to the WLC.
Why wrong: Incorrect because DHCP option 43 is used for APs in different subnets; since APs are in the same VLAN, they can use Layer 2 CAPWAP discovery and do not need option 43.
- C
The APs are running an incompatible IOS version that does not support CAPWAP.
Why wrong: Incorrect because CAPWAP is supported on most modern APs; version incompatibility would typically cause a different error, not a failure to join.
- D
The APs must be assigned a static IP address to join the WLC.
Why wrong: Incorrect because APs can use DHCP to obtain an IP address; static IP is not a requirement for CAPWAP discovery.
Quick Answer
The answer is that the WLC does not have a CAPWAP source interface configured. This is the most likely cause because, although the APs can ping the WLC’s management IP, CAPWAP discovery requires the WLC to respond from a consistent and explicitly defined source IP address. Without a CAPWAP source interface, the WLC may not properly advertise itself for AP join requests, even when both devices reside on the same VLAN. On the ENCOR 350-401 exam, this scenario tests your understanding of the CAPWAP discovery process and the common misconfiguration trap where engineers assume a reachable management IP is sufficient. A frequent distractor is DHCP option 43, but that is only needed when APs are in a different subnet. Remember the memory tip: “Ping is not join”—reachability does not guarantee CAPWAP discovery. Always verify the WLC’s CAPWAP source interface under the interface configuration to ensure the APs have a stable target for their discovery requests.
CCNP Wireless Infrastructure Practice Question
This 350-401 practice question tests your understanding of wireless infrastructure. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 deploying a new wireless LAN controller (WLC) in a campus network. The WLC must manage 200 access points across three buildings. The engineer configures the WLC with a management IP address and enables CAPWAP. However, the access points fail to join the WLC. The APs are in the same VLAN as the WLC and can ping the WLC's management IP. What is the most likely cause of the APs not joining?
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 WLC does not have a CAPWAP source interface configured.
The correct answer is that the APs are unable to discover the WLC via CAPWAP because the WLC's CAPWAP source interface is not configured or is misconfigured. Even though the APs can ping the management IP, CAPWAP discovery requires the WLC to respond from a consistent source IP. The other options are less likely: DHCP option 43 is not needed if APs are in the same subnet, APs do not need a specific IOS version to join, and APs do not need a static IP if they can obtain one via DHCP.
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 WLC does not have a CAPWAP source interface configured.
Why this is correct
Correct because the CAPWAP source interface must be configured on the WLC so that APs can discover and communicate with it. Without it, the WLC may not respond to CAPWAP discovery requests.
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 APs are not configured with DHCP option 43 to point to the WLC.
- ✗
The APs are running an incompatible IOS version that does not support CAPWAP.
Why it's wrong here
Incorrect because CAPWAP is supported on most modern APs; version incompatibility would typically cause a different error, not a failure to join.
- ✗
The APs must be assigned a static IP address to join the WLC.
Why it's wrong here
Incorrect because APs can use DHCP to obtain an IP address; static IP is not a requirement for CAPWAP discovery.
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.
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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Wireless Infrastructure — study guide chapter
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FAQ
Questions learners often ask
What does this 350-401 question test?
Wireless Infrastructure — This question tests Wireless Infrastructure — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The WLC does not have a CAPWAP source interface configured. — The correct answer is that the APs are unable to discover the WLC via CAPWAP because the WLC's CAPWAP source interface is not configured or is misconfigured. Even though the APs can ping the management IP, CAPWAP discovery requires the WLC to respond from a consistent source IP. The other options are less likely: DHCP option 43 is not needed if APs are in the same subnet, APs do not need a specific IOS version to join, and APs do not need a static IP if they can obtain one via DHCP.
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
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