Switch Stack PoE Exhaustion Causing AP Reboots
A distribution center uses a Mist-managed Juniper EX Series stack with two 48-port PoE+ switches, each with a 740 W PoE budget. The stack powers 38 Wi-Fi 6 APs, 12 PTZ cameras, and 6 access-control readers. The APs are configured with a 30 W PoE+ draw; cameras draw 12 W during the day and 22 W when IR turns on at night; readers draw 5 W. At 02:00, the night shift reports APs rebooting in waves, and Mist Wired Assurance shows AP flapping, PoE port power-denied events, and LLDP neighbor loss on the affected ports. The switch uplink is 10 Gbps and shows no errors. The customer recently added the cameras and changed the AP port profile to 'PoE+ always on.' Marvis recommends checking PoE budget. The team asks whether the issue is wireless, switch hardware, or power budgeting, and what to change before the next night shift.
1. Calculate the PoE load and determine whether the issue is a power budget problem. Explain why per-switch distribution matters.
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Calculate per switch, not stack aggregate. Each switch has 740 W. If one switch has 28 APs at 30 W = 840 W, it is already over budget before cameras. Total load is 38 x 30 + 12 x 22 + 6 x 5 = 1,140 + 264 + 30 = 1,434 W, close to the 1,480 W combined budget, but the per-switch and per-port distribution matters. The 02:00 timing matches cameras turning on IR and drawing 22 W. PoE power-denied and AP flapping are consistent with budget exhaustion, not wireless. Check the PoE budget per switch, port allocation, and whether 'PoE+ always on' reserves max power.
2. How would you use Mist Wired Assurance and Marvis to confirm the root cause and rule out other causes?
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Use Wired Assurance to confirm: switch PoE budget utilization, per-port power draw, power-denied events, and AP flapping correlated with camera IR schedule. Marvis recommending PoE budget is a strong signal, but verify LLDP neighbor loss and port errors. Rule out STP loops and uplink congestion; the 10 Gbps uplink has no errors. Check whether APs are on one switch and cameras on the other; if one switch carries most APs, it will exhaust first. Also check PoE+ versus PoE and cable length/quality.
3. Recommend remediation and validation steps before the next night shift.
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Rebalance ports so no switch exceeds about 80% of 740 W; move cameras to a separate PoE switch or add a PSU/switch. Reduce AP power draw where possible by using the correct PoE class and disabling unused features; do not set 'always on' max unless needed. Schedule camera IR or use lower-power cameras if possible. Add a second PoE switch for cameras, or upgrade to a higher PoE budget. After changes, monitor Wired Assurance for 48 hours: no power-denied events, stable AP uptime, and normal LLDP. Verify APs do not reboot at 02:00.