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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter12 Configuring Interface Characteristics
Configuring Ethernet Interfaces
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 49-13. 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 actual power consumption of the devices, and the switch adjusts the power
budget according ly. The CDP protocol works with Cisco powered devices and does not apply to IEEE
third-party powered devices. For these devices, wh en 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 Class0
(class status unknown) or a Class 3, the switch budgets 15,400 milliwatts for the device, regardless of
the actual amount of power needed. If the powered device reports a higher class than its actual
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.
For example, if the switch budgets 15,400 milliwatts on each PoE port, you can connect only 24 Class0
powered devices. If your Class0 device power requirement is actually 5000 milliwatts, you can set the
consumption wattage to 5000 milliwatts and connect up to 48 devices. The total PoE output power
available on a 24-port or 48-port switch is 370,000 milliwatts.
Caution You should carefully plan your switch power budget and make certain not to oversubscribe the power
supply.
Note When you manually configure the power budget, you must also consider the power loss over the cable
between the switch and the powered device.
When you enter the power inline consumption default wattage or the no power inline consumption
default global configuration command, or the power inline consumption wattage or the no power
inline consumption interface configuration command this caution message appears:
%CAUTION: Interface interface-id: Misconfiguring the 'power inline consumption/allocation'
command may cause damage to the switch and void your warranty. Take precaution not to
oversubscribe the power supply.
Refer to documentation.
If the power supply is over-subscribed to by up to 20 percent, the switch continues to operate but its
reliability is reduced. If the power supply is subscribed to by more than 20 percent, the short-circuit
protection circuitry triggers and shuts the switch down.
Step5 show power inline [interface-id |
module switch-number]
Display PoE status for a switch or switch stack, for the specified
interface, or for a specified stack member.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose