Cisco Catalyst 3560-X Software Configuration Manual page 414
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Also See for Catalyst 3560-X:
- Command reference manual (1188 pages) ,
- Software configuration manual (1438 pages) ,
- Manual (276 pages)
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Interface Types
without CDP or LLDP, the switch does not allow devices to consume more than 15.4 W of power because
values from 15400 to 30000 mW are only allocated based on CDP or LLDP requests. If a powered device
consumes more than 15.4 W without CDP or LLDP negotiation, the device might be in violation of the
maximum current (Imax) limitation and might experience an Icut fault for drawing more current than the
maximum. The port remains in the fault state for a time before attempting to power on again. If the port
continuously draws more than 15.4 W, the cycle repeats.
When a powered device connected to a PoE+ port restarts and sends a CDP or LLDP packet with a power
Note
TLV, the switch locks to the power-negotiation protocol of that first packet and does not respond to
power requests from the other protocol. For example, if the switch is locked to CDP, it does not provide
power to devices that send LLDP requests. If CDP is disabled after the switch has locked on it, the switch
does not respond to LLDP power requests and can no longer power on any accessories. In this case, you
should restart the powered device.
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 0.05% 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 on power on the
PoE port, the switch does not police the real-time power consumption of the device, and the device can
consume more power than the maximum allocated amount, which could adversely affect the switch and
the devices connected to the other PoE ports.
Because a standalone switch supports internal power supplies, the total amount of power available for
the powered devices varies depending on the power supply configuration.
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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
1-12
If a power supply is removed and replaced by a new power supply with less power and the switch
does not have enough power for the powered devices, the switch denies power to the PoE ports in
auto mode in descending order of the port numbers. If the switch still does not have enough power,
the switch then denies power to the PoE ports in static mode in descending order of the port numbers.
If the new power supply supports more power than the previous one and the switch now has more
power available, the switch grants power to the PoE ports in static mode in ascending order of the
port numbers. If it still has power available, the switch then grants power to the PoE ports in auto
mode in ascending order of the port numbers.
Chapter 1
Configuring Interface Characteristics
OL-25303-03
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Troubleshooting
