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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
With PoE+, powered devices use IEEE 802.3at and LLDP power with media dependent interface (MDI)
type, length, and value descriptions (TLVs), Power-via-MDA TLVs, for negotiating power up to 30 W.
Cisco pre-standard devices and Cisco IEEE powered devices can use CDP or the IEEE 802.3at
power-via-MDI power negotiation mechanism to request power levels up to 30 W.
Note The intitial 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 the maximum
of 30 W.
Note The CDP-specific power consumption requirement is referred to as the actual power consumption
requirement in the Catalyst 3750 and 3560 software configuration guides and command references.
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.
The Catalyst 3750-X stackable switch also supports StackPower, which allows the power supplies to
share the load across multiple systems in a stack when you connect the switches with power stack cables.
You can manage the power supplies of up to four stack members as a one large power supply For more
information about StackPower, see Chapter 9, “Configuring Catalyst 3750-X StackPower.”
Power Management Modes
The switch supports these PoE modes:
• auto—The switch automatically detects if the connected device requires power. If the switch
discovers a powered device connected to the port and if the switch has enough power, it grants
power, updates the power budget, turns on power to the port on a first-come, first-served basis, and
updates the LEDs. For LED information, see the hardware installation guide.
If the switch has enough power for all the powered devices, they all come up. If enough power is
available for all powered devices connected to the switch, power is turned on to all devices. If there
is not enough available PoE, or if a device is disconnected and reconnected while other devices are
waiting for power, it cannot be determined which devices are granted or are denied power.
If granting power would exceed the system power budget, the switch denies power, ensures that
power to the port is turned off, generates a syslog message, and updates the LEDs. After power has
been denied, the switch periodically rechecks the power budget and continues to attempt to grant the
request for power.
If a device being powered by the switch is then connected to wall power, the switch might continue
to power the device. The switch might continue to report that it is still powering the device whether
the device is being powered by the switch or receiving power from an AC power source.
If a powered device is removed, the switch automatically detects the disconnect and removes power
from the port. You can connect a nonpowered device without damaging it.
You can specify the maximum wattage that is allowed on the port. If the IEEE class maximum
wattage of the powered device is greater than the configured maximum value, the switch does not
provide power to the port. If the switch powers a powered device, but the powered device later
requests through CDP messages more than the configured maximum value, the switch removes
power to the port. The power that was allocated to the powered device is reclaimed into the global
power budget. If you do not specify a wattage, the switch delivers the maximum value. Use the auto
setting on any PoE port. The auto mode is the default setting.