Using the commands described in this chapter, you can:
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Enable or disable PoE operation on individual ports.
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Monitor PoE status and performance.
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Configure a non-default power threshold for SNMP and Event Log reporting of PoE consumption on either all PoE ports on the switch or on all PoE ports.
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Specify the port priority you want to use for provisioning PoE power in the event that the PoE resources become oversubscribed.
A PSE detects the power needed by a connected PD before supplying that power via a phase referred to as "searching". If the PSE cannot supply the required amount of power, it does not supply any power. For PoE using a Type 1 device, a PSE will not supply any power to a PD unless the PSE has at least 17 watts available. For example, if a PSE has a maximum available power of 382 watts and is already supplying 378 watts, and is then connected to a PD requiring 10 watts, the PSE will not supply power to the PD.
For PoE+ using Type 2 devices, the PSE must have at least 33 watts available.
In the default configuration, all ports in a HP switch covered in this guide are configured to support PoE operation. You can:
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Disable or re-enable per-port PoE operation on individual ports to help control power usage and avoid oversubscribing PoE resources.
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Configure per-port priority for allocating power in case a PoE device becomes oversubscribed and must drop power for some lower-priority ports to support the demand on other, higher-priority ports.
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Manually allocate the amount of PoE power for a port by usage, value, or class.
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Allocate PoE power based on the link-partner’s capabilities via LLDP.
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![[NOTE: ]](images/note.gif) |
NOTE: The ports support standard networking links and PoE links. You can connect either a non-PoE device or a PD to a port enabled for PoE without reconfiguring the port. |
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To best utilize the allocated PoE power, spread your connected PoE devices as evenly as possible. Depending on the amount of power the power supply device delivers to a PoE switch, there may or may not always be enough power available to connect and support PoE operation on all the ports. When a new PD connects to a PoE switch and the switch does not have enough power left for that port:
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If the new PD connects to a port “X” having a higher PoE priority than another port “Y” that is already supporting another PD, then the power is removed from port “Y” and delivered to port “X”. In this case the PD on port “Y” loses power and the PD on port “X” receives power.
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If the new PD connects to a port “X” having a lower priority than all other PoE ports currently providing power to PDs, then power is not supplied to port “X” until one or more PDs using higher priority ports are removed.
In the default configuration (usage), when a PD connects to a PoE port and begins operating, the port retains only enough PoE power to support the PD's operation. Unused power becomes available for supporting other PD connections. However, if you configure the poe-allocate-by option to either value or class, all of the power configured is allocated to the port.
For PoE (not PoE+), while 17 watts must be available for a PoE module on the switch to begin supplying power to a port with a PD connected, 17 watts per port is not continually required if the connected PD requires less power. For example, with 20 watts of PoE power remaining available on a module, you can connect one new PD without losing power to any connected PDs on that module. If that PD draws only 3 watts, 17 watts remain available, and you can connect at least one more PD to that module without interrupting power to any other PoE devices connected to the same module. If the next PD you connect draws 5 watts, only 12 watts remain unused. With only 12 unused watts available, if you then connect yet another PD to a higher-priority PoE port, the lowest-priority port on the module loses PoE power and remains unpowered until the module once again has 17 or more watts available. (For information on power priority, see Power priority operation.)
For PoE+, there must be 33 watts available for the module to begin supplying power to a port with a PD connected.
Disconnecting a PD from a PoE port makes that power available to any other PoE ports with PDs waiting for power. If the PD demand for power becomes greater than the PoE power available, power is transferred from the lower-priority ports to the higher-priority ports. (Ports not currently providing power to PDs are not affected.)
If a PSE can provide power for all connected PD demand, it does not use its power priority settings to allocate power. However, if the PD power demand oversubscribes the available power, then the power allocation is prioritized to the ports that present a PD power demand. This causes the loss of power from one or more lower-priority ports to meet the power demand on other, higher-priority ports. This operation occurs regardless of the order in which PDs connect to the switch’s PoE-enabled ports.
There are two ways that PoE power is prioritized:
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Using a priority class method, a power priority of Low (the default), High, or Critical is assigned to each enabled PoE port.
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Using a port-number priority method, a lower-numbered port has priority over a higher-numbered port within the same configured priority class, For example, port A1 has priority over port A5 if both are configured with High priority.