Hands-On Lab: Power over Ethernet (PoE) Basics

Lab Objective

Verify PoE status and power consumption on a switch port connected to a powered device, and configure power priority so a critical device is protected if the switch's total power budget is exceeded.

Lab Purpose

PoE eliminates the need for separate electrical wiring to devices like IP phones, wireless access points, and security cameras, but every switch has a finite total power budget shared across all its ports. Engineers must know how to verify actual power draw and how to prioritize critical devices when that budget is tight.

Lab Topology

Switch1 ---- Gi1/0/1 ---- IP Phone
Switch1 ---- Gi1/0/2 ---- Wireless Access Point

Both devices are PoE-powered by Switch1

Task 1: Verify PoE Is Enabled on the Switch Ports

Confirm PoE is active (the default) on both Gi1/0/1 and Gi1/0/2.

Task 2: Check Power Consumption Per Port

Display how much power each connected device is actually drawing.

Task 3: Check Total Switch Power Budget

Display the switch's total available and currently used power budget.

Task 4: Configure Power Priority

Configure the IP phone's port with a higher power priority than the access point's port, so the phone remains powered first if the total budget becomes insufficient.

Task 5: Simulate a Power Shortage Response

Explain what happens if a newly connected high-power device would exceed the switch's remaining budget, given the priority configured above.

Solution and Verification

Switch1# show power inline gigabitethernet1/0/1

Interface  Admin  Oper       Power(Watts)  Device
Gi1/0/1    auto   on         6.3           IP Phone

Switch1# show power inline gigabitethernet1/0/2

Interface  Admin  Oper       Power(Watts)  Device
Gi1/0/2    auto   on         12.9          AIR-AP

Switch1# show power inline

Available:370.0(w)  Used:19.2(w)  Remaining:350.8(w)

Switch1(config)# interface gigabitethernet1/0/1
Switch1(config-if)# power inline priority high

Switch1(config)# interface gigabitethernet1/0/2
Switch1(config-if)# power inline priority low

Switch1# show power inline gigabitethernet1/0/1 | include Priority

Priority: high

-- With this priority set, if the switch's total
-- power budget were ever exceeded by a newly
-- connected device, the switch would deny power
-- to the LOWER-priority access point port first,
-- before ever removing power from the HIGH-priority
-- IP phone port -- protecting voice service
-- specifically during a power-constrained situation

Key Takeaway

show power inline is the essential command for confirming both individual port draw and the switch's overall remaining budget — and configuring power priority ensures that if the budget is ever exceeded, the switch makes a deliberate choice about which devices lose power rather than an arbitrary one, protecting genuinely critical devices like IP phones over less critical ones.