The answer is RF interference from the cordless phone base. This is correct because cordless phones commonly operate in the 2.4 GHz ISM band, the same frequency range used by Wi-Fi, creating co-channel interference that degrades signal quality and throughput. Since the 5 GHz band operates on a different frequency, it remains unaffected, which is why the technician sees the problem isolated to the 2.4 GHz band. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of how non-Wi-Fi devices can cause cordless phone interference on 2.4 GHz Wi-Fi, often appearing as a troubleshooting question where you must identify the source of intermittent drops or slow speeds. A common trap is assuming the issue is distance or obstructions, but the key clue is the router’s proximity to the phone base station. For a memory tip, think “2.4 GHz is the crowded band—phones, microwaves, and Bluetooth all share the space, so if 5 GHz is fine, suspect a 2.4 GHz neighbor.”
220-1101 Wireless Networking Technologies Practice Question
This 220-1201 practice question tests your understanding of wireless networking technologies. 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 technician is troubleshooting a home network where the 5 GHz band works fine, but the 2.4 GHz band is extremely slow and drops connections. The router is placed near a cordless phone base station. Which type of interference is most likely occurring?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
RF interference from the cordless phone base
Cordless phones often operate in the 2.4 GHz ISM band, causing co-channel interference with Wi-Fi. This degrades 2.4 GHz performance while leaving 5 GHz unaffected.
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.
✗
Bluetooth interference
Why it's wrong here
Bluetooth also uses 2.4 GHz but typically causes less sustained disruption than a cordless phone base station.
✗
Microwave oven interference
Why it's wrong here
Microwaves cause intermittent interference when in use, not constant; the issue is persistent.
✗
Co-channel interference from a neighboring Wi-Fi network
Why it's wrong here
This could affect both bands, but the 5 GHz band is fine, pointing to a specific 2.4 GHz interferer.
✓
RF interference from the cordless phone base
Why this is correct
Cordless phones operating at 2.4 GHz cause continuous interference, explaining the poor performance on that band.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
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 220-1201 OSPF questions on adjacency and route selection.
Wireless Networking Technologies — This question tests Wireless Networking Technologies — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: RF interference from the cordless phone base — Cordless phones often operate in the 2.4 GHz ISM band, causing co-channel interference with Wi-Fi. This degrades 2.4 GHz performance while leaving 5 GHz unaffected.
What should I do if I get this 220-1201 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 220-1201 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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