Information About Poe - Cisco Catalyst 2960 series Configuration Manual

Information about PoE

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 PoE feature operates the same whether or not the switch is a stack member. The power budget is per
switch and independent of any other switch in the stack. Election of a new active switch does not affect PoE
operation. The active switch keeps track of the PoE status for all switches and ports in the stack and includes
the status in output displays.
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.
• 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 is consuming
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.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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