Lessons · Network switches · power over Ethernet
Power down the same cable
A PoE port supplies power as well as data, so a phone, a camera or an access point needs no socket at the far end.
Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.
What it is for
It is why a camera can go where there is no power, and the reason a switch has a power budget: the total it can supply is finite and the devices draw from it.
How to think about it
Count the budget before you plan the ports. A switch that can deliver 370 watts will not run twenty devices asking for 25 each, and finding that out by plugging things in is an expensive way to learn arithmetic.
Worked example
enableThe # prompt.
configure terminalInto configuration mode.
interface gi0/7The port with the camera on it.
description CCTV camera, loading baySay what is drawing the power, so the budget can be read from the descriptions.
switchport mode accessAccess.
switchport access vlan 45The camera VLAN. Cameras belong away from everything else.
spanning-tree portfastOne device on the end.
endOut.
show interfaces statusThe port and its description. On real hardware `show power inline` adds what each port is actually drawing.
Your turn
Put the camera in the camera VLAN.
switchport access vlan
Console into a switch
The trap
Treating the port count as the limit. Eight PoE ports does not mean eight devices at full power; the shared budget is the real limit and it is a number in the datasheet.