Power Over Ethernet (PoE/PoE+) Operation > Configuring PoE operation

  

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Configuring PoE operation

In the default configuration, PoE support is enabled on the ports in a PoE switch. The default priority for all ports is Low and the default power notification threshold is 80 (%).

Using the CLI, you can:

  • Disable or re-enable PoE operation on individual PoE ports

  • Enable support for pre-standard devices

  • Change the PoE priority level on individual PoE ports

  • Change the threshold for generating a power level notice

  • Manually allocate the amount of PoE power for a port by usage, value, or class

  • Allocate PoE power based on the link-partner’s capabilities via LLDP

Disabling or re-enabling PoE port operation

Syntax:

[no] interface <port-list> power-over-ethernet

Re-enables PoE operation on <port-list> and restores the priority setting in effect when PoE was disabled on <port-list>.

The no form of the command disables PoE operation on <port-list>.

Default: All PoE ports are initially enabled for PoE operation at Low priority. If you configure a higher priority, this priority is retained until you change it.

Enabling support for pre-standard devices

The HP switches covered in this guide also support some pre-802.3af devices. For a list of the supported devices, see the FAQ for your switch model.

Syntax:

[no] power-over-ethernet pre-std-detect

Detects and powers pre-802.3af standard devices.
[NOTE: ]

NOTE: The default setting for the pre-std-detect PoE parameter changed. In earlier software the default setting is “on”. The default setting is “off”.

Configuring the PoE port priority

Syntax:

interface <port-list> power-over-ethernet [ critical | high | low ]

Reconfigures the PoE priority level on <port-list>. For a given level, ports are prioritized by port number in ascending order. For example, if ports A1-A24 have a priority level of critical, port A1 has priority over ports A2-A24.

If there is not enough power available to provision all active PoE ports at a given priority level, the lowest-numbered port at that level is provisioned first. PoE priorities are invoked only when all active PoE ports cannot be provisioned (supplied with PoE power)

Critical Specifies the highest-priority PoE support for <port-list>. The active PoE ports at this level are provisioned before the PoE ports at any other level are provisioned.
High Specifies the second priority PoE support for <port-list>. The active PoE ports at this level are provisioned before the Low priority PoE ports are provisioned.
Low (Default) Specifies the third priority PoE support for <port-list>. The active PoE ports at this level are provisioned only if there is power available after provisioning any active PoE ports at the higher priority levels.

Controlling PoE allocation

The default option for PoE allocation is usage, which is what a PD attached to the port is allocated. You can override this value by specifying the amount of power allocated to a port by using the class or value options.

Syntax:

[no] int <port-list> poe-allocate-by [ usage | class | value ]

Allows you to manually allocate the amount of PoE power for a port by either its class or a defined value.

usage The automatic allocation by a PD
class Uses the power ramp-up signature of the PD to identify which power class the device will be in. Classes and their ranges are shown in Power classes and their values.
value A user-defined level of PoE power allocated for that port.
[NOTE: ]

NOTE: The allowable PD requirements are lower than those specified for PSEs to allow for power losses along the Cat-5 cable.

Power classes and their values

Power class Value
0

Depends on cable type and PoE architecture. Maximum power level output of 15.4 watts at the PSE.

This is the default class; if there is not enough information about the load for a specific classification, the PSE classifies the load as class 0 (zero).
1 Requires at least 4 watts at the PSE.
2 Requires at least 7 watts at the PSE.
3 15.4 watts
4

For PoE+

Maximum power level output of 30 watts at the PSE.

Example:

To allocate by class for ports 6 to 8:

HP Switch(config)# int 6-8 PoE-allocate-by class

Manually configuring PoE power levels

You can specify a power level (in watts) allocated for a port by using the value option. This is the maximum amount of power that will be delivered.

To configure a port by value:

  1. Set the PoE allocation by entering the poe-allocate-by value command:

    HP Switch(config) # int A6 poe-allocate-by value

    or in interface context:

    HP Switch(eth-A6) # poe-allocate-by value

  2. Select a value:

    HP Switch(config) # int A6 poe-value 15

    or in interface context:

    HP Switch(eth-A6) # poe-value 15

To view the settings, enter the show power-over-ethernet command, shown in PoE allocation by value and the maximum power delivered.

PoE allocation by value and the maximum power delivered

HP Switch(config)# show power-over-ethernet A6

 Status and Counters - Port Power Status for port A6

  Power Enable     : Yes
                                       LLDP Detect     : enabled
  Priority         : low               Configured Type :
  AllocateBy       : value             Value           : 15 W 1


  Detection Status : Delivering        Power Class     : 2

  Over Current Cnt : 0                 MPS Absent Cnt  : 0
  Power Denied Cnt : 0                 Short Cnt       : 0

  Voltage          : 55.1 V            Current         : 154 mA
  Power            : 8.4 W

1

Maximum power delivered.

If you set the PoE maximum value to less than what the PD requires, a fault occurs, as shown in PoE power value set too low for the PD.

PoE power value set too low for the PD

HP Switch(config)# int A7 poe-value 4

HP Switch(config)# show power-over-ethernet A7

 Status and Counters - Port Power Status for port A7

  Power Enable     : Yes
                                       LLDP Detect     : enabled
  Priority         : low               Configured Type :
  AllocateBy       : value             Value           : 4 W
  Detection Status : fault 1

             Power Class     : 2

  Over Current Cnt : 1                 MPS Absent Cnt  : 0
  Power Denied Cnt : 2                 Short Cnt       : 0

  Voltage          : 55.1 V            Current         : 154 mA
  Power            : 8.4 W

1

‘Fault’ appears when the PoE power value is set too low.

Configuring PoE redundancy

When PoE redundancy is enabled, PoE redundancy occurs automatically. The switch keeps track of power use and will not supply PoE power to additional PoE devices trying to connect if that results in the switch not having enough power in reserve for redundancy if one of the power supplies should fail.

Syntax:

[no] power-over-ethernet redundancy [ n+1 | full ]

Allows you to set the amount of power held in reserve for redundancy.

no

Means that all available power can be allocated to PDs.

Default: No PoE redundancy enforced.
n+1

One of the power supplies is held in reserve for redundancy. If a single power supply fails, no powered devices are shut down.

If power supplies with different ratings are used, the highest-rated power supply is held in reserve to ensure full redundancy.
full Half of the available power supply is held in reserve for redundancy. If power supplies with different ratings are used, the highest-rated power supply is held in reserve to ensure full redundancy.

For more information about PoE redundancy and power supplies, see the PoE/PoE+ Planning and Implementation Guide, available on the HP website at www.hp.com/networking. Auto search the model number for your switch, For example, “HP Switch 2920”, then select the device from the list, and click on Product manuals. Click on the “Setup and install — general” link under Manuals.

Changing the threshold for generating a power notice

You can configure one of the following thresholds:

  • A global power threshold that applies to all ports on the switch. This setting acts as a trigger for sending a notice when the PoE power consumption on any PoE port installed in the switch crosses the configured global threshold level. (Crossing the threshold level in either direction—PoE power usage either increasing or decreasing— triggers the notice.) The default setting is 80%.

  • A per-slot power threshold that applies to an individual PoE module installed in the designated slot. This setting acts as a trigger for sending a notice when the module in the specified slot exceeds or goes below a specific level of PoE power consumption.

Syntax:

power-over-ethernet [ slot <slot-id-range> ] threshold <1-99>

This command specifies the PoE usage level (as a percentage of the PoE power available on a module) at which the switch generates a power usage notice. This notice appears as an SNMP trap and a corresponding Event Log message and occurs when a PoE module's power consumption crosses the configured threshold value. That is, the switch generates a notice whenever the power consumption on a module either exceeds or drops below the specified percentage of the total PoE power available on the module.

This command configures the notification threshold for PoE power usage on either a global or per-module (slot) basis.

Without the [slot PoE <slot-id-range>] option, the switch applies one power threshold setting on all PoE modules installed in the switch.

Example:

Suppose slots A, B, and C each have a PoE module installed. In this case, executing the following command sets the global notification threshold to 70% of available PoE power:

HP Switch(config)# power-over-ethernet threshold 70

With this setting, if module B is allocated 100 watts of PoE power and is using 68 watts, and then another PD is connected to the module in slot B that uses 8 watts, the 70% threshold of 70 watts is exceeded. The switch sends an SNMP trap and generates this Event Log message:

Slot B POE usage has exceeded threshold of 70%.

If the switch is configured for debug logging, it also sends the Event Log message to the configured debug destination(s).

On any PoE module, if an increasing PoE power load (1) exceeds the configured power threshold (which triggers the log message and SNMP trap), and then (2) later decreases and drops below the threshold again, the switch generates another SNMP trap, plus a message to the Event Log and any configured Debug destinations.

To continue the preceding Example:, if the PoE power usage on the PoE module in slot B drops below 70%, another SNMP trap is generated and you will see this message in the Event Log:

Slot B POE usage is below threshold of 70%.

For a message listing, please see the Event Log Message Reference Guide for your switch. Go to www.hp.com/networking; auto search the model number for your switch, for Example: “HP Switch 2920”, then select the device from the list and click on Product manuals. Click on the “User guide” link under Manuals.

(Default Global PoE Power Threshold: 80). By using the [slot <slot-id-range>]option, you can specify different notification thresholds for different PoE modules installed in the switch. For example, you could set the power threshold for a PoE module in slot “A” to 75% and the threshold for the module in slot “B” to 68% by executing the following two commands:

HP Switch(config)# power-over-ethernet slot a threshold 75

HP Switch(config)# power-over-ethernet slot b threshold 68
[NOTE: ]

NOTE: The last threshold command affecting a given slot supersedes the previous threshold command affecting the same slot. Thus, executing the following two commands in the order shown sets the threshold for the PoE module in slot “D” to 75%, but leaves the thresholds for any PoE modules in the other slots at 90%.

HP Switch(config)# power-over-ethernet threshold 90

HP Switch(config)# power-over-ethernet slot d threshold 75

If you reverse the order of the above two commands, all PoE modules in the switch will have a threshold of 90%.

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