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Port Management: PoE
PoE on the Device
!
CAUTION
Cisco Small Business 300 Series Managed Switch Administration Guide
You can decide the following:
•
Maximum power a PSE is allowed to supply to a PD
•
During device operation, to change the mode from Class Power Limit to
Port Limit and vice versa. The power values per port that were configured
for the Port Limit mode are retained.
Changing the mode from Class Limit to Port limit and vice versa when
NOTE
the device is operational forces the Powered Device to reboot.
•
Maximum port limit allowed as a per-port numerical limit in mW (Port Limit
mode).
•
To generate a trap when a PD tries to consume too much and at what
percent of the maximum power this trap is generated.
The PoE-specific hardware automatically detects the PD class and its power limit
according to the class of the device connected to each specific port (Class Limit
mode).
If at any time during the connectivity an attached PD requires more power from the
device than the configured allocation allows (no matter if the device is in Class
Limit or Port Limit mode), the device does the following:
•
Maintains the up/down status of the PoE port link
•
Turns off power delivery to the PoE port
•
Logs the reason for turning off power
•
Generates an SNMP trap
Consider the following when connecting switches capable of supplying PoE:
The PoE models of the Sx200, Sx300, and Sx500 series switches are PSE (Power
Sourcing Equipment) that are capable of supplying DC power to attaching PD
(Powered Devices). These devices include VoIP phones, IP cameras, and wireless
access points. The PoE switches can detect and supply power to pre-standard
legacy PoE Powered Devices. Due to the support of legacy PoE, it is possible that
a PoE device acting as a PSE may mistakenly detect and supply power to an
attaching PSE, including other PoE switches, as a legacy PD.
Even though Sx200/300/500 PoE switches are PSE, and as such should be
powered by AC, they could be powered up as a legacy PD by another PSE due to
false detection. When this happens, the PoE device may not operate properly and
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