CCNA Network Infrastructure and Connectivity Practice Question
Which TWO statements correctly compare 802.11ac and 802.11ax features?
⚠ Common exam trap
Cisco often tests the misconception that higher QAM values (like 1024-QAM) are backward-compatible across Wi-Fi generations, but 802.11ac is limited to 256-QAM, and 802.11ax is the first to support 1024-QAM.
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
✓
802.11ax uses OFDMA, while 802.11ac uses OFDM.
802.11ax (Wi‑Fi 6) introduces Orthogonal Frequency Division Multiple Access (OFDMA), which allows multiple users to share subcarriers simultaneously, improving efficiency in dense environments. In contrast, 802.11ac (Wi‑Fi 5) uses Orthogonal Frequency Division Multiplexing (OFDM), where each transmission occupies the entire channel for a single user, leading to less efficient channel utilization. Option C is correct: WPA3 is mandatory for Wi‑Fi 6 (802.11ax) certification, while for 802.11ac it is optional—devices can still obtain Wi‑Fi 5 certification with WPA2 only. Option B is incorrect because 802.11ac supports a maximum of 256‑QAM; 1024‑QAM is first introduced with 802.11ax. Option D is wrong: 802.11ac operates exclusively in the 5 GHz band, but 802.11ax operates in both 2.4 GHz and 5 GHz. Option E is false: both standards support 20, 40, 80, and 160 MHz channel widths; 802.11ac does not exclusively use 80 MHz, and 802.11ax does not use 160 MHz exclusively.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
802.11ax uses OFDMA, while 802.11ac uses OFDM.
Why this is correct
Orthogonal Frequency-Division Multiple Access (OFDMA) is a key 802.11ax feature that subdivides the channel into smaller resource units, allowing multiple clients to transmit concurrently in the same frame. In contrast, 802.11ac relies on Orthogonal Frequency-Division Multiplexing (OFDM), where a single client can use the entire set of subcarriers during its transmission slot. OFDMA reduces contention and overhead in dense networks, and this is the central PHY-layer difference between the two standards.
- ✗
Both 802.11ac and 802.11ax support 1024-QAM modulation.
Why it's wrong here
802.11ac supports modulation up to 256-QAM, whereas 802.11ax introduces 1024-QAM to increase peak data rates when signal-to-noise ratio is high. Although 802.11ac Wave 2 products may claim high efficiency, 1024-QAM is not part of the 802.11ac specification and remains a distinguishing feature of Wi-Fi 6. Therefore, saying both standards support 1024-QAM is false; the higher-order modulation is unique to 802.11ax among these two.
- ✓
WPA3 is mandatory for 802.11ax and optional for 802.11ac.
Why this is correct
The Wi-Fi 6 (802.11ax) certification program mandates WPA3 as a baseline security requirement for all devices, ensuring stronger encryption and more robust authentication. For 802.11ac (Wi-Fi 5), WPA3 is not mandatory because the standard was finalized before WPA3 existed; some vendors add it via firmware updates, but it remains an optional enhancement. This distinction is about certification compliance and supported security features, not an inherent PHY or MAC requirement.
- ✗
Both standards use only the 5 GHz band.
Why it's wrong here
802.11ac is specified to operate only in the 5 GHz band, but 802.11ax (Wi-Fi 6) is designed to support both 2.4 GHz and 5 GHz bands, with Wi-Fi 6E adding 6 GHz. Therefore, saying both standards use only 5 GHz is false. The dual-band support in 802.11ax is critical for backward compatibility and in congested 2.4 GHz environments where many legacy devices still operate.
- ✗
802.11ac uses 80 MHz channels, while 802.11ax uses 160 MHz channels exclusively.
Why it's wrong here
The claim that 802.11ac uses 80 MHz channels and 802.11ax uses 160 MHz exclusively misrepresents the channelization. Both standards support 20, 40, 80, and 160 MHz channel widths, with 160 MHz support introduced in 802.11ac Wave 2 and carried forward into 802.11ax. In the 2.4 GHz band, 802.11ax typically uses only 20 or 40 MHz because of regulatory constraints and narrow channel availability, so 160 MHz is definitely not exclusive to 802.11ax.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓802.11ax uses OFDMA, while 802.11ac uses OFDM.Correct answer▾
Why this is correct
Orthogonal Frequency-Division Multiple Access (OFDMA) is a key 802.11ax feature that subdivides the channel into smaller resource units, allowing multiple clients to transmit concurrently in the same frame. In contrast, 802.11ac relies on Orthogonal Frequency-Division Multiplexing (OFDM), where a single client can use the entire set of subcarriers during its transmission slot. OFDMA reduces contention and overhead in dense networks, and this is the central PHY-layer difference between the two standards.
✗Both 802.11ac and 802.11ax support 1024-QAM modulation.Wrong answer — click to see why▾
Why this is wrong here
802.11ac supports up to 256-QAM, not 1024-QAM. 1024-QAM is introduced in 802.11ax to achieve higher data rates by encoding more bits per symbol. Stating that both support 1024-QAM is factually incorrect.
Why candidates choose this
Students may confuse the modulation advancements in Wi-Fi generations, assuming that 1024-QAM is available in both since 802.11ac Wave 2 introduced some enhancements. However, 1024-QAM is exclusive to 802.11ax.
✗Both standards use only the 5 GHz band.Wrong answer — click to see why▾
Why this is wrong here
802.11ac operates exclusively in the 5 GHz band, while 802.11ax supports both 2.4 GHz and 5 GHz bands. The statement incorrectly claims both use only 5 GHz, ignoring 802.11ax's backward compatibility with 2.4 GHz.
Why candidates choose this
Since 802.11ac is known for 5 GHz operation, students might assume 802.11ax also only uses 5 GHz, especially because early marketing focused on 5 GHz improvements. However, 802.11ax includes 2.4 GHz for better range and compatibility.
✗802.11ac uses 80 MHz channels, while 802.11ax uses 160 MHz channels exclusively.Wrong answer — click to see why▾
Why this is wrong here
Both 802.11ac and 802.11ax support multiple channel widths: 20, 40, 80, and 160 MHz. 802.11ac Wave 2 introduced 160 MHz, and 802.11ax also supports it. The statement incorrectly claims 802.11ac uses only 80 MHz and 802.11ax uses only 160 MHz.
Why candidates choose this
Students may recall that 802.11ac commonly uses 80 MHz channels and that 160 MHz is a newer feature, leading them to think 802.11ac is limited to 80 MHz. However, both standards support a range of channel widths.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
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Senior Network & Security Engineer · founder of Courseiva
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