Cisco Systems 3750E manual Budgeting Power for Devices Connected to a PoE Port, 11-27

Chapter 11 Configuring Interface Characteristics

Configuring Ethernet Interfaces

	Command	Purpose
Step 3
	power inline {auto [max max-wattage]	Configure the PoE mode on the port. The keywords have these meanings:
	never static [max max-wattage]}	• auto—Enable powered-device detection. If enough power is
		available, automatically allocate power to the PoE port after device
		detection. This is the default setting.
		• (Optional) max max-wattage—Limit the power allowed on the port.
		The range is 4000 to 15400 mW. If no value is specified, the
		maximum is allowed (15400 mW).
		• never—Disable device detection, and disable power to the port.
		Note If a port has a Cisco powered device connected to it, do not use
		the power inline never command to configure the port. A false
		link-up can occur, placing the port into the error-disabled state.
		• static—Enable powered-device detection. Pre-allocate (reserve)
		power for a port before the switch discovers the powered device. The
		switch reserves power for this port even when no device is connected
		and guarantees that power will be provided upon device detection.
		The switch allocates power to a port configured in static mode before it
		allocates power to a port configured in auto mode.
Step 4
	end	Return to privileged EXEC mode.
Step 5
	show power inline [interface-id	Display PoE status for a switch or a switch stack, for the specified
	module switch-number]	interface, or for a specified stack member.
		The module switch-numberkeywords are supported only on
		Catalyst 3750-E switches.
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

For information about the output of the show power inline user EXEC command, see the command reference for this release. For more information about PoE-related commands, see the “Troubleshooting Power over Ethernet Switch Ports” section on page 45-13. For information about configuring voice VLAN, see Chapter 15, “Configuring Voice VLAN.”

Budgeting Power for Devices Connected to a PoE Port

When Cisco powered devices are connected to PoE ports, the switch uses Cisco Discovery Protocol (CDP) to determine the CDP-specificpower consumption of the devices, and the switch adjusts the power budget accordingly. This does not apply to IEEE third-party powered devices. For these devices, when the switch grants a power request, the switch adjusts the power budget according to the powered-device IEEE classification. If the powered device is a class 0 (class status unknown) or a class 3, the switch budgets 15,400 mW for the device, regardless of the CDP-specific amount of power needed. If the powered device reports a higher class than its CDP-specific consumption or does not support power classification (defaults to class 0), the switch can power fewer devices because it uses the IEEE class information to track the global power budget.

By using the power inline consumption wattage configuration command, you can override the default power requirement specified by the IEEE classification. The difference between what is mandated by the IEEE classification and what is actually needed by the device is reclaimed into the global power budget for use by additional devices. You can then extend the switch power budget and use it more effectively.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		11-27