Cisco IE 4000, Руководство по настройке программного обеспечения

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24
Configuring Interfaces
Understanding Interface Types
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 Maximum Power Allocation (Cutoff Power) on a PoE Port, page 24.
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.
Maximum Power Allocation (Cutoff Power) on a PoE Port
When power policing is enabled, the switch determines one of the these values as the cutoff power on the PoE port in
this order:
1. Manually when you set the user-defined power level that the switch budgets for the port by using the power inline
consumption default wattage global or interface configuration command
2. Manually when you set the user-defined power level that limits the power allowed on the port by using the power
inline auto max max-wattage or the power inline static max max-wattage interface configuration command
3. Automatically when the switch sets the power usage of the device by using CDP power negotiation or by the IEEE
classification
4. Automatically when the switch sets the power usage to be the default value of 15400 mW
Use the first or second method in the previous list to manually configure the cutoff-power value by entering the power
inline consumption default wattage or the power inline [ auto | static max ] max-wattage command. If you are not
manually configuring the cutoff-power value, the switch automatically determines the value by using CDP power
negotiation or the device IEEE classification, which is the third method in the previous list. If the switch cannot determine
the value by using one of these methods, it uses the default value of 15400 mW (the fourth method in the previous list).
Power Consumption Values
You can configure the initial power allocation and the maximum power allocation on a port. However, these values are
only the configured values that determine when the switch should turn on or turn off power on the PoE port. The maximum
power allocation is not the same as the actual power consumption of the powered device. The actual cutoff power value
that the switch uses for power policing is not equal to the configured power value.
When power policing is enabled, the switch polices the power usage at the switch port , which is greater than the power
consumption of the device. When you are manually set the maximum power allocation, you must consider the power loss
over the cable from the switch port to the powered device. The cutoff power is the sum of the rated power consumption
of the powered device and the worst-case power loss over the cable.
The actual amount of power consumed by a powered device on a PoE port is the cutoff-power value plus a calibration
factor of 500 mW (0.5 W). The actual cutoff value is approximate and varies from the configured value by a percentage
of the configured value. For example, if the configured cutoff power is 12 W, the actual cutoff-value is 11.4 W, which is
5% less than the configured value.
We recommend that you enable power policing when PoE is enabled on your switch. For example, if policing is disabled
and you set the cutoff-power value by using the
power inline auto max 6300 interface configuration command, the
configured maximum power allocation on the PoE port is 6.3 W (6300 mW). The switch provides power to the connected
devices on the port if the device needs up to 6.3 W. If the CDP-power negotiated value or the IEEE classification value
exceeds the configured cutoff value, the switch does not provide power to the connected device. After the switch turns