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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 13 Configuring Interface Characteristics
Interface Types
• static—The switch pre-allocates power to the port (even when no powered device is connected) and
guarantees that power will be available for the port. The switch allocates the port configured
maximum wattage, and the amount is never adjusted through the IEEE class or by CDP messages
from the powered device. Because power is pre-allocated, any powered device that uses less than or
equal to the maximum wattage is guaranteed to be powered when it is connected to the static port.
The port no longer participates in the first-come, first-served model.
However, if the powered-device IEEE class is greater than the maximum wattage, the switch does
not supply power to it. If the switch learns through CDP messages that the powered device needs
more than the maximum wattage, the switch shuts down the powered device.
If you do not specify a wattage, the switch pre-allocates the maximum value. The switch powers the
port only if it discovers a powered device. Use the static setting on a high-priority interface.
• never—The switch disables powered-device detection and never powers the PoE port even if an
unpowered device is connected. Use this mode only when you want to make sure that power is never
applied to a PoE-capable port, making the port a data-only port.
For information on configuring a PoE port, see the “Configuring a Power Management Mode on a PoE
Port” section on page 13-32.
Power Monitoring and Power Policing
When policing of the real-time power consumption is enabled, the switch takes action when a powered
device consumes more power than the maximum amount allocated, also referred to as the cutoff-power
value.
When PoE is enabled, the switch senses the real-time power consumption of the powered device. The
switch monitors the real-time power consumption of the connected powered device; this is called power
monitoring or power sensing. The switch also polices the power usage with the power policing feature.
Power monitoring is backward-compatible with Cisco intelligent power management and CDP-based
power consumption. It works with these features to ensure that the PoE port can supply power to the
powered device. For more information about these PoE features, see the “Supported Protocols and
Standards” section on page 13-7.
The switch senses the real-time power consumption of the connected device as follows:
1. The switch monitors the real-time power consumption on individual ports.
2. The switch records the power consumption, including peak power usage. The switch reports the
information throu gh the CISCO-POWER-ETHERNET-EXT-MIB.
3. If power policing is enabled, the switch polices power usage by comparing the real-time power
consumption to the maximum power allocated to the device. For more information about the
maximum power consumption, also referred to as the cutoff power, on a PoE port, see the
“Maximum Power Allocation (Cutoff Power) on a PoE Port” section on page 13-11.
If the device uses more than the maximum power allocation on the port, the switch can either turn
off power to the port, or the switch can generate a syslog message and update the LEDs (the port
LED is now blinking amber) while still providing power to the device based on the switch
configuration. By default, power-usage policing is disabled on all PoE ports.
If error recovery from the PoE error-disabled state is enabled, the switch automatically takes the PoE
port out of the error-disabled state after the specified amount of time.
If error recovery is disabled, you can manually re-enable the PoE port by using the shutdown and
no shutdown interface configuration commands.
4. If policing is disabled, no action occurs when the powered device consumes more than the maximum
power allocation on the PoE port, which could adversely affect the switch.