Power over Ethernet (PoE) Switches
Access points can receive their power over Ethernet cables from Power over
Ethernet (PoE) switches, routers with PoE switch modules, or midspan
power injectors, thus alleviating the need for electrical outlets near them.
APs require up to 15W of power, so plan your power budget accordingly.
Two power standards are the Cisco Prestandard PoE and the IEEE’s 802.3af
standard. Both have a method for sensing that a powered device is connected
to the port. 802.3af specifies a method for determining the amount of power
needed by the device. Cisco devices, when connected to Cisco switches, can
additionally use CDP to send that information. Power can be supplied over
the data pairs—1, 2, 3, and 6—or over the unused pairs of 4, 5, 7, and 8.
Cisco PoE switches are configured by default to automatically detect and
provide power. To disable this function, or to re-enable it, use the interface
command power inline {never | auto}. To view interfaces and the power
allotted to each, use show power inline [interface].