12-7
Catalyst 2928 Switch Software Configuration Guide
OL-23389-01
Chapter 12 Configuring Interface Characteristics
Understanding Interface Types
Power monitoring is backward-compatible with Cisco intelligent power management and CDP-based
power consumption. It works with these features to ensure that the PoE port can supply power to the
powered device. For more information about these PoE features, see the
Initial Power Allocation” section on page 12-5
.
The switch senses the power consumption of the connected device as follows:
1.
The switch monitors the real-time power consumption on individual ports.
2.
The switch records the power consumption, including peak power usage, and reports the information
through an SNMP MIB, CISCO-POWER-ETHERNET-EXT-MIB.
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 the
“Maximum Power Allocation (Cutoff Power) on a PoE Port” section on page 12-7.
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 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 and LLDP power negotiation.
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 do not manually configure the cutoff-power value, the switch
automatically determines the value by using CDP power negotiation. If the switch cannot determine the
value by using one of these methods, it uses the default value of 15.4 W.
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.
