The initial allocation for Class 0, Class 3, and Class 4 powered devices is 15.4 W. When a device starts up and uses CDP or LLDP to send a request for more than 15.4 W, it can be allocated up to a maximum of 30 W.

The CDP-specific power consumption requirement is referred to as the actual power consumption requirement in the Cisco Catalyst Switches software configuration guides and command references.

You can connect a nonpowered device on a PoE port without damaging the device.

The Cisco intelligent power management method is backward-compatible with the CDP with power consumption method which means that the device responds according to the CDP message that it receives.

If the switch detects a fault caused by an undervoltage, overvoltage, overtemperature, oscillator fault, or short-circuit condition, it turns off power to the port, generates a syslog message, and updates the power budget and LEDs.

By default, IEEE 802.3bt mode is enabled on the Cisco UPOE switch.

If a specific wattage is not configured, the maximum value is configured by default.

If the maximum power level allowed for an IEEE class exceeds the configured maximum wattage, the PoE switch does not provide power to the port.

If a switch has multiple PoE ports and each PoE port has a powered device connected to it, then

• If enough power is available for all PoE ports, then all PoE ports are changed to the Up state and LEDs are updated.

• If all powered devices require power and enough power is available, then power is turned on for all devices.

• If enough PoE is not available, and

  • all powered devices remain connected, then all powered devices do not receive power.

  • a powered device is disconnected and reconnected while other devices are waiting for power, it is not possible to determine which devices are granted or denied power.

If a powered device requests additional power that exceeds the power budget, the device is denied power, power to the port is turned off, a syslog message is generated, and. LEDs are updated. The switch periodically rechecks the power budget and continues to attempt to grant the power request.

If a powered device, that is receiving power from a PoE-capable switch, is also connected to a power source, the PoE-capable switch continues to power the device. The switch continues to report that it is providing power to the device irrespective of whether the device is actually getting power from the PoE-capable switch or the power source.

If a powered device is removed from a PoE port, the PoE-capable switch detects the disconnect and removes power from the port.

If the device supplies power to a powered device, but the powered device later requests through CDP messages more than the configured maximum value, the device removes power to the port. The global power budget reclaims the power that was allocated to the powered device.

If a specific wattage is not configured, the maximum value is configured by default.

The PoE port is powered only if it discovers a powered device.

The port is not part of the first-come, first-served model.

The switch allocates the port-configured maximum wattage, and the power is not changed even if the powered device is assigned to an IEEE class or sends CDP messages.

If the PoE switch learns through CDP messages that the powered device is consuming more than the maximum wattage, the switch shuts down the powered device.