• Supported Platforms
• EX Series

• Related Topics
• Example: Configuring PoE Interfaces on an EX Series Switch
• Example: Configuring PoE Interfaces with Different Priorities on an EX Series Switch

PoE and EX Series Switches Overview

PoE and PoE+

PoE was first defined in the IEEE 802.3af standard. In this standard, the amount of power that can be supplied to a powered device is limited to 15.4 W. PoE+, which was defined in the later IEEE 802.3at standard, increases the amount of power to 30 W. The PoE+ standard provides support for legacy PoE devices—an IEEE 802.3af (PoE) powered device can operate normally when connected to IEEE 802.3at (PoE+) power sourcing equipment.

Whether an EX Series switch supports PoE, PoE+, or neither depends on the switch model. Consult your switch hardware guide for information on PoE or PoE+ support.

Note: This topic and its related topics hereafter use the term PoE to refer to both PoE and PoE+. When it is necessary to distinguish between the two PoE standards, the terms IEEE 802.3af (PoE) and IEEE 802.at (PoE+) are used.

PoE Power Management

Switches that have PoE ports have a PoE controller that keeps track of the PoE power consumption on the switch and allocates power to the PoE ports. The following factors determine how the PoE controller allocates power to the PoE ports:

• PoE Power Budget
• Power Management Mode
• PoE Interface Power Priority

PoE Power Budget

The PoE controller allocates power to the PoE ports from a set PoE power budget. The PoE power budget varies according to switch model and, for switches that support power supplies of different capacities, the capacity of the installed power supply. For example, a Juniper Networks EX3200 Ethernet Switch with a 320 W power supply has a PoE power budget of 130 W, while with a 600 W power supply it has a PoE power budget of 410 W.

In switches that support power supplies of different capacities, if you change your existing power supply to a lower-capacity power supply, the PoE power budget might no longer be sufficient to power all the PoE ports on the switch. If your switch supports redundant power supplies and you have installed power supplies of different capacities, the PoE power budget is based on the wattage of the lower-capacity power supply. The number of PoE ports on the switch cannot be increased by installing a larger power supply.

You can display the PoE power budget for your switch by using the show poe controller command.

Power Management Mode

EX Series switches support two power management modes: class and static. The mode you configure for your switch determines how the maximum power for a PoE interface is derived and how power is allocated to the PoE interfaces:

• Class mode—In this mode, the maximum power for an interface is determined by the class of connected powered device. Table 1 lists the classes of powered devices and associated power levels.

  Table 1: Class of Powered Device and Power Levels

  Standard	Class	Maximum Power Delivered by PoE Port	Power Range of Powered Device
  IEEE 802.3af (PoE) and IEEE 802.3at (PoE+)	0	15.4 W	0.44 through 12.95 W
  	1	4.0 W	0.44 through 3.84 W
  	2	7.0 W	3.84 through 6.49 W
  	3	15.4 W	6.49 through 12.95 W
  IEEE 802.3at (PoE+)	4	30.0 W	12.95 through 25.5 W

  The powered device communicates to the PoE controller which class it belongs to when it is connected. The PoE controller then allocates to the interface the maximum power required by the class (see Table 1). It does not allocate power to an interface until a powered device is connected. Class 0 is the default class for powered devices that do not provide class information. Class 4 powered devices are supported only by switches that support IEEE 802.3at (PoE+).

• Static mode—In this mode, you specify the maximum power for each PoE interface. The PoE controller then allocates this amount of power to the interface from its total budget. For example, if you specify a maximum value of 8.0 W for ge-/0/0/3, the PoE controller allocates 8.0 W out of its total power budget for the interface. This amount is allocated to the interface whether or not a powered device is connected to the interface or whether the connected powered device uses less power than 8.0 W.

  For switches that support IEEE 802.3af (PoE), the maximum power permitted on any interface is 15.4 W. This wattage guarantees that, after line loss, the powered device receives 12.95 W, which is the maximum required by 802.3af-compliant powered devices.

  For switches that support IEEE 802.3at (PoE+), the maximum power permitted on any interface is 30.0 W. This wattage guarantees that, after line loss, the powered device receives 25.5 W, which is the maximum required by 802.3at-compliant powered devices.

In both class and static mode, if the power consumption of a powered device exceeds the maximum power allocated to the interface, power to the interface is turned off.

PoE Interface Power Priority

You can configure a PoE interface to have either a high or low power priority. The power priority determines which interfaces receive power if PoE power demands are greater than the PoE power budget. If the total power allocated for all interfaces exceeds the switch budget, the lower priority interfaces are turned off and the power allocated to those interfaces drops to 0. Thus you should set interfaces that connect powered devices such as security cameras and emergency phones to high priority.

Among PoE interfaces that have the same assigned priority, power priority is determined by the port number, with lower-numbered ports having higher priority.

PoE Configuration and Monitoring

The factory default configuration enables PoE on switches that support PoE. By default, the power management mode is class, and the power priority of all interfaces is low.

If the default configuration meets your needs, you do not need to configure PoE before you connect powered devices to the switch.

To monitor the powered devices and to manage PoE power consumption, you can use the CLI or J-Web interface to display the current power consumption of the PoE ports. You can also enable the monitoring of power consumption on a port over time and then view the collected records using the CLI or the J-Web interface.