- A
Co-channel interference from neighboring access points using the same channel.
Correct because multiple APs on the same channel cause co-channel interference, leading to collisions and poor performance.
- B
Adjacent channel interference from access points using channels 10 and 12.
Why wrong: Incorrect because adjacent channel interference would occur if channels overlapped, but the scenario states other APs are using channel 11, not adjacent channels.
- C
Non-WiFi interference from devices like microwaves or cordless phones.
Why wrong: Incorrect because the spectrum analyzer showed high utilization on channel 11, but non-WiFi interference would likely affect multiple channels or be intermittent.
- D
The access point is overloaded with too many clients.
Why wrong: Incorrect because client overload would cause high utilization but not necessarily the specific pattern of disconnections; co-channel interference is more likely given neighboring APs.
Quick Answer
The answer is co-channel interference from neighboring access points using the same channel. This occurs because multiple APs operating on channel 11 in the 2.4 GHz band create contention and collisions, forcing clients to wait for clear airtime, which directly causes slow speeds and frequent disconnections. On the ENCOR 350-401 exam, this scenario tests your ability to differentiate co-channel interference from adjacent-channel interference—a common trap where students confuse overlapping channels (e.g., channels 10 and 11) with the same-channel contention described here. The key distinction is that co-channel interference stems from APs sharing an identical channel, not merely overlapping ones, and it degrades performance through increased backoff and retransmissions. A helpful memory tip: think “same channel, same fight” to recall that co-channel interference is about APs competing on the same frequency, not adjacent spillover.
350-401 Wireless Infrastructure Practice Question
This 350-401 practice question tests your understanding of wireless infrastructure. 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 wireless network where clients in a specific area report slow speeds and frequent disconnections. The engineer uses a spectrum analyzer and finds high utilization on channel 11 in the 2.4 GHz band. The engineer also notices that several neighboring access points are using channel 11. What is the most likely cause of the issue?
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
Co-channel interference from neighboring access points using the same channel.
The correct answer is co-channel interference from neighboring APs using the same channel. This causes contention and collisions, degrading performance. Adjacent channel interference would occur if channels overlapped (e.g., channels 10 and 11), but the scenario specifies same channel. Non-WiFi interference is possible but not indicated. Client load on a single AP would cause high utilization but not necessarily disconnections.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Co-channel interference from neighboring access points using the same channel.
Why this is correct
Correct because multiple APs on the same channel cause co-channel interference, leading to collisions and poor performance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Adjacent channel interference from access points using channels 10 and 12.
Why it's wrong here
Incorrect because adjacent channel interference would occur if channels overlapped, but the scenario states other APs are using channel 11, not adjacent channels.
- ✗
Non-WiFi interference from devices like microwaves or cordless phones.
Why it's wrong here
Incorrect because the spectrum analyzer showed high utilization on channel 11, but non-WiFi interference would likely affect multiple channels or be intermittent.
- ✗
The access point is overloaded with too many clients.
Why it's wrong here
Incorrect because client overload would cause high utilization but not necessarily the specific pattern of disconnections; co-channel interference is more likely given neighboring APs.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
Incorrect because the spectrum analyzer showed high utilization on channel 11, but non-WiFi interference would likely affect multiple channels or be intermittent.
Scenario analysis trap
Incorrect because adjacent channel interference would occur if channels overlapped, but the scenario states other APs are using channel 11, not adjacent channels.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 350-401 question test?
Wireless Infrastructure — This question tests Wireless Infrastructure — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Co-channel interference from neighboring access points using the same channel. — The correct answer is co-channel interference from neighboring APs using the same channel. This causes contention and collisions, degrading performance. Adjacent channel interference would occur if channels overlapped (e.g., channels 10 and 11), but the scenario specifies same channel. Non-WiFi interference is possible but not indicated. Client load on a single AP would cause high utilization but not necessarily disconnections.
What should I do if I get this 350-401 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
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?
OSPF neighbours must agree on key parameters.
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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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