802.11ac Wave 2 AP Upgrade: Which Switch Limitation Matters?
An engineer is upgrading the legacy APs to 802.11ac Wave 2 capable APs. The existing gigabit uplinked switches provide 802.3at. Which switch limitation is a concern?
Community Votes
100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The question tests whether you can separate switch port bandwidth from PoE power budget; the trap is assuming 802.3at cannot power a Wave 2 AP.
Upgrading legacy APs to 802.11ac Wave 2 APs on gigabit PoE+ switches raises a wired throughput concern: Wave 2 APs can exceed 1 Gbps over the air. This page establishes that interface throughput (A) is the switch limitation, not 802.3at power.
Choosing D (output power) because 802.3at is older, but PoE+ delivers up to 30W, which is sufficient for typical 802.11ac Wave 2 APs.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
802.11ac Wave 2 APs support PHY rates well beyond 1 Gbps, especially with 4x4 MU-MIMO, 80+80 MHz channels, and multi-user transmissions. The existing gigabit Ethernet uplink on the switch becomes the bottleneck because the AP cannot push its full wireless capacity through a 1 Gbps wired port. As Jonycici explained, Wave 2 APs "can support higher data rates that exceed 1 Gbps" and this "can prevent the APs from achieving their full performance potential." The switch already provides 802.3at (PoE+), which supplies up to 30W and is adequate for typical Wave 2 APs, so the real limitation is interface throughput, making A the correct choice.Why the Other Options Are Wrong
B (high availability) is a design consideration for controller or AP redundancy, not a switch limitation tied to AP upgrade bandwidth. C (collision domains) is irrelevant in modern full-duplex switched networks where each port is its own collision domain and collisions are effectively eliminated. D (output power) is the strongest distractor: 802.3at delivers up to 30W at the PSE and 25.5W at the powered device, which is enough for most 802.11ac Wave 2 APs. Farhad123 correctly noted that "802.3at can support up to 30w and for 802.11ac this amount should be enough," so D does not represent the concern in this scenario.Community Comment Notes
The community overwhelmingly selected A. Jonycici reasoned that the gigabit interface creates a bottleneck when Wave 2 APs exceed 1 Gbps. Farhad123 agreed with A and pointed out that 802.3at's 30W power is sufficient for 802.11ac. NightmareCreature initially leaned toward D due to PoE concerns, but acknowledged that "the switch is already gigabit capable," which actually reinforces the throughput limitation. The comments collectively show that power is a common trap while wired bandwidth is the actual design issue.Exam Strategy
In 300-425 design questions, always separate power budget from uplink bandwidth. 802.3at (PoE+) provides enough power for most Wave 2 APs, so when the switch is already gigabit, look for wired throughput exceeding 1 Gbps as the bottleneck. Verify switch port speed and PoE standard independently.
Frequently Asked Questions
Why is output power not the switch limitation for 802.11ac Wave 2 APs?
802.3at (PoE+) provides up to 30W at the switch port, which is enough for typical Wave 2 APs; the bottleneck is the 1 Gbps wired uplink.
Can a gigabit uplink support 802.11ac Wave 2 APs?
It can power them and pass traffic, but it may not carry the full wireless throughput since Wave 2 APs can exceed 1 Gbps over the air.