internet – The Lazy Networker

Power over Ethernet (PoE) allows network cables to carry both data and electrical power to devices like IP phones, wireless access points, and security cameras, eliminating the need for separate power adapters.

PoE Standards

Standard	Max Power per Port	Devices Supported
802.3af (PoE)	15.4W	Phones, small APs
802.3at (PoE+)	30W	High-power APs, cameras
802.3bt (PoE++)	60-100W	LED lights, laptops

How to Enable PoE on a Cisco Switch

Most Cisco switches support PoE by default, but you can manually enable or configure it.

1. Check if the Switch Supports PoE

Run:

Switch#show power inline

If you see available power and usage stats, the switch supports PoE.

2. Enable PoE on an Interface

Run:

Switch#conf t
interface <interface_id>
power inline auto
exit

<interface_id> → Example: GigabitEthernet1/0/1
auto → Enables PoE when a powered device (PD) is detected.

To disable PoE on a port:

Switch#conf t
interface <interface_id>
power inline never
exit

3. Set Power Limits for Devices

By default, the switch assigns power dynamically. You can manually set power limits:

Switch#conf t
interface <interface_id>
power inline static max 20000
exit

Max power in milliwatts (mW)
- 15000 for 15W (PoE)
- 30000 for 30W (PoE+)
- 60000 for 60W (PoE++)

To check power consumption:

Switch#show power inline interface <interface_id> detail

4. Troubleshoot PoE Issues

If a device is not powering up:

Check PoE status:bashCopyEditshow power inline interface <interface_id>
Reset PoE on the port:bashCopyEditconf t interface <interface_id> power inline never power inline auto exit
If the port is err-disabled, recover it:bashCopyEditconf t interface <interface_id> shutdown no shutdown exit
If power is exhausted, check:bashCopyEditshow power inline

Summary

Task	Command
Enable PoE	`power inline auto`
Disable PoE	`power inline never`
Set power limit	`power inline static max <mW>`
Check PoE status	`show power inline`
Check port power use	`show power inline interface <interface_id> detail`