CompTIA Network+ (N10-009)Network TroubleshootingHard
A pilot deployment of 5 GHz wireless access points experiences intermittent client disconnections every 10–15 minutes. A Wi-Fi analyzer shows the APs briefly disappearing from channel 116 before reappearing on a different channel moments later. No other wireless devices are detected causing interference. What is the most likely explanation?
- AThe APs are exceeding their maximum client association limit
- BChannel bonding is causing excessive co-channel interference
- CDynamic Frequency Selection (DFS) is forcing the APs to change channels after detecting radar signals
- DThe APs have a duplex mismatch with the wired switch ports
Show answer & explanationAnswer & explanation
Correct answer: C. Dynamic Frequency Selection (DFS) is forcing the APs to change channels after detecting radar signals
Channels like 116 fall within the DFS (Dynamic Frequency Selection) range of the 5 GHz band, which is shared with radar systems (e.g., weather, military). When an AP detects radar-like signals, regulations require it to vacate the channel and switch to another, causing the exact symptom of the AP disappearing and reappearing on a new channel.
Why the other options are wrong
- A. An association limit would cause new connections to be refused, not periodic channel changes.
- B. Channel bonding affects throughput/interference but doesn't cause an AP to vacate a channel entirely.
- D. Duplex mismatch is a wired-side issue and wouldn't cause wireless channel changes.
Dynamic Frequency Selection (DFS)
A regulatory requirement for certain 5 GHz channels that forces access points to detect and avoid radar signals by switching channels, sometimes causing brief service interruptions.
- DFS channels overlap with radar-used frequencies (e.g., weather radar).
- APs must vacate a DFS channel within seconds of detecting radar-like signals.
- Symptom: brief AP dropouts followed by channel changes, without visible RF interference.
Memory trick: 'When radar knocks, DFS channels must vacate.'