Power over Ethernet (PoE)¶

PoE delivers electrical power to a connected device over the same cable as the data — no separate power supply needed for APs, cameras, and phones.

Standards¶

Standard	Common name	Max power at the port
802.3af	PoE	15.4W
802.3at	PoE+	30W
802.3bt Type 3	PoE++ (Cisco UPoE)	60W
802.3bt Type 4	PoE++ (Cisco UPoE+)	90W (71.3W assured at the device)

A 12-port PoE+ switch (e.g. Cisco's WS-C3560CX-12PD-S) provides up to 30W per port — comfortably enough for a Ruckus R650, which draws well under that.

Power delivered at the device is slightly less than what the port supplies, due to cable loss — long runs (near the 100m Ethernet limit) lose more than short ones. Rarely an issue in practice, but worth knowing if a device near its power ceiling behaves oddly only on a long cable run.

Configuration¶

! Current PoE allocation across all ports — see Cisco IOS CLI Reference
Switch# show power inline

Switch# configure terminal
Switch(config)# interface Gi0/1
! Enable PoE, negotiate power automatically with the connected device (default)
Switch(config-if)# power inline auto
! Disable PoE on this port entirely
Switch(config-if)# power inline never
! Reserve a fixed amount (mW) regardless of negotiation, for devices that don't negotiate properly
Switch(config-if)# power inline static max 15000

Two-Event Classification¶

A class-4 PD can negotiate 802.3at over LLDP and still be capped at 15.4W. Single-event classification caps the port in hardware at af, and the LLDP grant cannot exceed that cap — so the PSE answers a 25.5W request with 13.0W.

The signature, in show power inline Gi0/1 detail:

IEEE Class: 4
Power available to the device: 15.4
Power Negotiation Used: IEEE 802.3at LLDP
  Requested Power(W):  25.5                 25.5
  Allocated Power(W):  13.0                 25.5

Budget is not the cause — show power inline shows the switch with most of its capacity free.

Fix, per port:

Switch(config)# interface range Gi0/1-12
Switch(config-if-range)# power inline port 2-event
Switch(config-if-range)# shutdown
Switch(config-if-range)# no shutdown

The bounce is required: two-event classification only takes effect at the next PD detection, so an already-powered device keeps its old allocation until the link is re-made.

After it, the same port reads:

Power available to the device: 30.0
  Requested Power(W):  25.5                 25.5
  Allocated Power(W):  25.5                 25.5

Power Budget Planning¶

Every PoE switch has a total power budget, shared across all ports — it's not simply "30W × number of ports." Before connecting PoE devices, confirm the total draw fits within what the switch can actually supply:

Cisco IOS — privileged EXEC:

! Shows total available, allocated, and remaining budget
show power inline

Worked example:

Device	Typical draw
Ruckus R650 AP	~15–20W
Ruckus R650 AP (×2 total)	~30–40W

Two R650s comfortably fit within a 12-port PoE+ switch's budget even with headroom for future devices (cameras, VoIP phones) — but always check show power inline against the actual device count before an event, not just on paper.

Troubleshooting¶

Device not powering on: confirm the port is actually PoE-capable and not set to power inline never; confirm the cable is good (PoE won't negotiate reliably over a damaged run even if data still limps through)
Device powers on then drops: likely exceeding the port's or switch's power budget — check show power inline for a "power denied" or "faulty" status
AP powers on but coverage/throughput is poor: the AP may have negotiated only 802.3af power (bad cable, af-only injector, failed negotiation) and be running degraded while looking healthy — an R650 on 802.3af drops its 5GHz radio from 4×4 to 2×4 at reduced transmit power and disables its second Ethernet port, USB, and IoT radio. Check show power inline: an R650 should be allocated PoE+ (802.3at) power (it draws up to ~21.6W), not capped at 15.4W
Intermittent power: often a cable/connector issue rather than a switch config issue — see Common Issues