PoE - jibingl/CCNA-CCNP GitHub Wiki

Power over Ethernet

Name Standard Walts Powered Wire Pairs
Cisco Inline Power (ILP) not standard 7 2
PoE (Type 1) 802.3af 15 2
PoE+ (Type 2) 802.3at 30 2
UPoE (Type 3) 802.3bt 60 4
UPoE+ (Type 4) 802.3bt 100 4
            provide-power(DC)
  PD(Phone)-------ethernet---.
                  -           \       power-cable(AC)
  PD(IPcam)-------ethernet----- [=]-----------------------[outlet]
                   -          / PSE
  PD(AP)----------ethernet---`
  (Powered Device)              (Power Sourcing Equipment)

PoE has a process to determine if a connected device needs power, and how much power it needs:

  • When a device connects to a PoE-enabled port, the PSE (normally switch) sends low power signals, monitors the response, and determines how much power the PD needs.
  • If the device needs power, the PSE supplies the power to allow the PD to boot.
  • The PSE continues to monitor the PD and supply the required amount of power (but not too much).

Power Policing can be configured to prevent a PD from taking too much power.

  • power inline police configures power policing with the default settings: disable the port and send a Syslog message if a PD draws too much power.
  • power inline police action err-disable is equivalent to above.
  • power inline police action log doesn't shut down the interface instead to restart the interface and send a Syslog message.