Understanding PoE on EX Series Switches

 

Power over Ethernet (PoE) enables electric power, along with data, to be passed over a copper Ethernet LAN cable. Powered devices—such as VoIP telephones, wireless access points, video cameras, and point-of-sale devices—that support PoE can receive power safely from the same access ports that are used to connect personal computers to the network. This reduces the amount of wiring in a network, and also eliminates the need to position a powered device near an AC power outlet, making network design more flexible and efficient.

Note

We recommend that you do not connect an enabled PoE port on one switch to an enabled PoE port on a second switch. If there is a large voltage difference between the power supplies of the two switches, the resulting negative current will trigger a fail-safe mechanism that prevents the power sourcing equipment (PSE) from delivering power to the other PoE ports on that switch.

This topic describes PoE on Juniper Networks EX Series Ethernet Switches.

PoE, PoE+, Enhanced, and Four-pair 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. A later standard, IEEE 802.3at, defined PoE+, which increases the amount of power to 30 W. The PoE+ standard provides support for legacy PoE devices—an IEEE 802.3af powered device can operate normally when connected to IEEE 802.3at (PoE+) power sourcing equipment.

Starting with Juniper Networks Junos OS Release 11.1, Juniper Networks provides enhanced PoE on EX3200 and EX4200 switches. Enhanced PoE is a Juniper Networks extension to the IEEE 802.3af standard that provides power of up to 18.6 W per PoE port.

On EX4300-48MP switches, starting in Junos OS Release 18.2R1, Juniper Networks supports an extension to the IEEE 802.3at PoE+ standard that provides up to 95 W of power switches by increasing the number of wires carrying the power, utilizing all four pairs of wire in a standard RJ-45 Ethernet cable. In addition to providing more power, utilizing all four pairs of wire improves energy efficiency, greatly reducing the amount of power lost during cable transmission. PoE+ operating in four-pair mode can deliver up to 60 W (high power PoE) or 95 W (ultra-high power PoE).

Table 1 lists EX Series switches and line cards and the version of PoE they support.

Table 1: PoE Version Support

Switch or Line Card

PoE Version

EX2200 switch

(EX2200-C-12P-2G, EX2200-24P-4G, EX2200-48P-4G models)

PoE+ (IEEE 802.3at)

Note: Starting with Junos OS Release 12.2R1, PoE commands are enabled on all non-PoE-capable EX2200 switch models. The PoE commands do not provide any meaningful configuration on standalone non-PoE-capable switch models. However, in an EX2200 Virtual Chassis, you can execute PoE commands from a non-PoE-capable master switch to configure PoE on PoE-capable Virtual Chassis members.

EX2300 switch

( EX2300-C-12P, EX2300-24P, EX2300-48P, EX2300-24MP, EX2300-48MP models)

PoE (IEEE 802.3af) and PoE+ (IEEE 802.3at)

Note: Starting with Junos OS Release 18.1R2, PoE is supported on EX2300-24MP and EX2300-48MP switch models, including multigigabit interfaces.

EX3200 switch

(EX3200-24P, EX3200-24T, EX3200-48P, EX3200-48T models)

Enhanced PoE

EX3300 switch

(EX3300-24P, EX3300-48P models)

PoE+ (IEEE 802.3at)

EX3400 switch

(EX3400-24T, EX3400-24P, EX3400-48T, EX3400-48T-AFI, EX3400-48P models)

PoE+ (IEEE 802.3at)

EX4200 switch—P models

(EX4200-24P and EX4200-48P)

Enhanced PoE

EX4200 switch—PX models

(EX4200-24PX and EX4200-48PX)

PoE+ (IEEE 802.3at)

EX4300 switch—P models

(EX4300-24P and EX4300-48P)

PoE+ (IEEE 802.3at)

EX4300 switch—MP model

(EX4300-48MP)

PoE+ (IEEE 802.3at) and PoE+ in four-pair mode (high power and ultra-high power PoE)

EX4600 switch

(EX4600-40F-AFO and EX4600-40F-AFI)

PoE+ (IEEE 802.3at)

Note: PoE is supported on EX4600 switches only when they are part of a mixed Virtual Chassis with EX4300 switches.

EX6200-48P (48-port PoE+) line card

PoE+ (IEEE 802.3at)

EX8200-2XS-40P (40-port PoE+ with 4-port SFP and 2-port SFP+) line card

EX8200-48PL (2-port SFP+ and 48-port PoE+ 20 Gbps) line card

PoE+ (IEEE 802.3at)—Ports 0 through 11, and PoE (IEEE 802.3af)—remaining PoE ports.

Note

This topic and its related topics use the term PoE as a generic term for PoE, PoE+, enhanced PoE, high power PoE and ultra-high power PoE.

PoE Power Allocation

A switch or line card that supports PoE has a PoE controller that keeps track of the PoE power consumption on the switch or line card, and allocates power to the PoE ports. The following factors determine how the PoE controller allocates power to the PoE ports:

Maximum PoE Power Consumption

The maximum PoE power consumption is the total amount of power available for the PoE controller to allocate to all of the PoE interfaces. In allocating power, the PoE controller cannot exceed the maximum PoE power consumption.

How the maximum PoE power consumption is determined depends on the switch model:

Maximum PoE Power Consumption on EX2200, EX2300, EX3200, EX3300, EX3400, EX4200, and EX4300 Switches

The maximum PoE power consumption on EX2200, EX2300, EX3200, EX3300, EX3400, EX4200, and EX4300 switches depends on the switch model and the capacities of the power supplies installed. To find the maximum PoE power consumption for each switch model, see Table 2 for EX2200 switch models, Table 3 for EX2300 switch models, Table 4 for EX3200 switch models, Table 5 for EX3300 switch models, see Table 6 for EX3400 switch models, Table 7 for EX4200 switch models, and Table 8 for EX4300 switch models.

The maximum PoE power consumption for a switch is displayed in the Maximum power field in the output of the show poe controller CLI command. The exception to this would be when LLDP power negotiation is in use.

If your switch supports power supplies of different capacities, keep the following points in mind:

  • If you change your existing power supply to a lower-capacity power supply, the maximum PoE power consumption 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 maximum PoE power consumption is based on the wattage of the lowest-capacity power supply.

  • You cannot increase the number of PoE-capable ports on a switch by installing a power supply that has a higher capacity.

Table 2 lists the EX2200 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 2: Maximum PoE Power Consumption for EX2200 Switches

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX2200-C-12T

30 W

EX2200-C-12P

12

180 W

100 W

EX2200-24T

75 W

 

EX2200-24P

24

550 W

405 W

EX2200-24T-DC

100 W

EX2200-48T

75 W

EX2200-48P

48

550 W

405 W

Table 3 lists the EX2300 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 3: Maximum PoE Power Consumption for EX2300 Switches

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX2300-24P

24

450 W

370 W

EX2300-24T

65 W

EX2300-48P

48

850 W

740 W

EX2300-48T

90 W

EX2300-C-12P

12

170 W

124 W

EX2300-C-12T

-

40 W

-

EX2300-24MP

24

535 W

380 W

EX2300-48MP

48

1005 W

740 W

Table 4 lists the EX3200 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 4: Maximum PoE Power Consumption for EX3200 Switch Models

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX3200-24T

8

320 W

130 W

EX3200-48T

8

320 W

130 W

EX3200-24P

24

600 W

410 W

EX3200-48P

48

930 W

740 W

EX3200-24T-DC

-

190 W

-

EX3200-48T-DC

-

190 W

-

Table 5 lists the EX3300 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 5: Maximum PoE Power Consumption EX3300 Switch Models

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX3300-24T

100 W

EX3300-24P

24

550 W

405 W

EX3300-24T-DC

100 W

EX3300-48T

100 W

EX3300-48T-BF

100 W

EX3300-48P

48

900 W

740 W

Table 6 lists the EX3400 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 6: Maximum PoE Power Consumption for EX3400 Switches

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX3400-48P

48

920 W

  • 1440 W with two 920 W power supplies installed

  • 740 W with one 920 W power supply installed

EX3400-48T

-

150 W

-

EX3400-48T-AFI

150 W

-

EX3400-24P

24

600 W

  • 720 W with two 600 W power supplies installed

  • 370 W with one 600 W power supply installed

EX3400-24T

150 W

EX3400-24T-DC

150 W

Table 7 lists the EX4200 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 7: Maximum PoE Power Consumption for EX4200 Switch Models

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX4200-24T

8

320 W

130 W

EX4200-48T

8

320 W

130 W

EX4200-24P

24

600 W

410 W

EX4200-48P

48

930 W

740 W

EX4200-24PX

24

930 W

740 W

EX4200-48PX

48

930 W

740 W

EX4200-24F

-

320 W

-

EX4200-24F-DC

-

190 W

-

EX4200-24T-DC

-

190 W

-

EX4200-48T-DC

-

190 W

-

Table 8 lists the EX4300 switch models, number of PoE-enabled ports, power supply ratings, and maximum PoE power consumption.

Table 8: Maximum PoE Power Consumption for EX4300 Switch Models

Switch Model Number

Number of PoE-Enabled Ports

Power Supply Rating

Maximum PoE Power Consumption

EX4300-48P

48

1100 W

  • 1440 W with two 1100 W power supplies installed

  • 925 W with one 1100 W power supply installed

EX4300-48T

0

350 W

-

EX4300-48T-AFI

0

350 W

-

EX4300-24P

24

715 W

  • 720 W with two 715 W power supplies installed

  • 565 W with one 715 W power supply installed

EX4300-24T

0

350 W

-

EX4300-48T-DC

0

550 W

-

EX4300-48T-DC-AFI

0

550 W

-

EX4300-48MP

48

1400 W

Note: 1400 W PSU behaves as a 1100 W PSU at low line input voltage (90-110V AC input).

  • 1700 W with two 1400 W power supplies installed

  • 1030 W with one 1400 W power supply installed

Note

EX4300 switches support power supply redundancy. For information on PoE power availability in N+N configurations and different PSU combinations, see AC Power Supply in EX4300 Switches.

Maximum PoE Power Consumption on EX6200 and EX8200 Switches

For EX6200 and EX8200 switches, each line card that supports PoE has its own PoE controller and maximum PoE power consumption. The maximum PoE power consumption is allocated to the line card by the switch’s power management, while PoE power is allocated to the ports on the line card by the PoE controller. Because EX6200 and EX8200 switches can differ in the number and capacity of power supplies installed and in the number and types of line cards installed, the amount of power available for PoE power can vary for switches of the same model.

Power management allocates PoE power to line cards that support PoE only after it has allocated base power to and powered on all line cards. It then allocates the remaining power to the line cards for PoE in order of line card power priority. (In a default configuration, power priority is determined by the line card slot number, with slot 0 having the highest priority.) If the remaining power is insufficient to provide PoE power to all PoE line cards, a low-priority line card might receive no PoE power or partial PoE power.

By default, power management allocates enough PoE power to a line card to power all PoE ports at their maximum supported power. If the powered devices connected to that line card require less power than that, you can configure a smaller maximum PoE power consumption for the line card. For example, power management normally allocates 915 W of PoE power to a 48-port PoE+ 20 Gbps (EX8200-48PL) line card. If the powered devices connected to that line card consume no more than a total of 250 W, you can set the maximum PoE power consumption for the line card to 250 W. Doing so frees 665 W, which then can be used to fulfill the PoE power needs of lower-priority line cards.

You can also configure the power priority of the PoE ports on a line card. If power management is unable to allocate enough power to a line card to meet its maximum PoE power consumption, the line card’s PoE controller turns off power to PoE ports in reverse priority order as required to meet the reduced power allocation.

Power management adjusts PoE power allocations as power availability and demand in a switch change. As a general rule, power management allocates power to power on line cards before it allocates PoE power. For example, if you add a line card and there is insufficient power available to power it on, power management reduces the PoE power it provides to line cards, starting with the lowest priority line card, until it frees enough power to power on the new line card. When power management reduces the maximum PoE power consumption for a line card because of insufficient power, it logs a message in the system log.

Note that the actual power consumed by the powered devices does not affect power management’s power allocation for a line card. If you have set the maximum PoE power consumption for a line card to 500 W, power management allocates 500 W even if the powered devices are consuming less power than that. Similarly, the maximum PoE power consumption is not increased if you add additional powered devices—if the powered devices require more than the 500 W maximum that you have configured, lower-priority devices do not receive power.

You can display the switch’s power budget maintained by power management, including its PoE power allocations, by using the show chassis power-budget-statistics command. You can also display the maximum PoE power consumption for each line card in a switch by using the show poe controller command.

For more information about how power management allocates power, including PoE power, see Understanding Power Management on EX Series Switches.

PoE Interface Power Allocation

The maximum power for a PoE interface is the maximum amount of power that can be provided by that interface. If the actual power consumption of a powered device connected to a PoE interface exceeds the maximum power allocated to that interface, the switch turns off power to the interface.

The maximum power for a PoE interface is allocated by the PoE controller. One of the three methods listed below is used, on a per interface basis, to determine maximum power. The methods are listed in order of priority.

Class PoE Management Mode

In the class PoE management mode, the maximum power for an interface is determined by the class of the connected powered device. The PoE standards IEEE 802.3af and IEEE 802.3at define classes of powered devices based on the levels of power that they require. Table 9 lists the classes of powered devices and associated power levels.

Table 9: 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

High power PoE (PoE+ in four-pair mode)

0

30.8 W

0.88 through 25.9 W

1

8.0 W

0.88 through 7.86 W

2

14.0 W

7.86 through 12.98 W

3

30.8 W

12.98 through 25.9 W

4

60.0 W

25.9 through 51 W

Ultra-high power PoE (PoE+ in four-pair mode)

0-4

95.0 W

71 W

Because of line loss, the power range of the powered device is less than the maximum power delivered at the PoE port for each class. Line loss is influenced by cable length, cable quality, and other factors and is typically less than 16 percent of the maximum power.

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 9). 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 by PoE ports that support only IEEE 802.3at (PoE+).

By default, when the management option is set to class and LLDP is enabled, LLDP power negotiation is also enabled on supported switches. See LLDP Power Negotiation for more information.

Static PoE Management Mode

In the static PoE management mode, you specify the maximum power for each PoE interface. The PoE controller then allocates this amount of power to the interface from the maximum PoE power consumption for the switch or line card. For example, if you specify a maximum value of 8.0 W for ge-0/0/3, the PoE controller allocates 8.0 W for this interface out of the maximum power consumption. This amount is allocated to the interface irrespective of whether a powered device is connected to the interface or the connected powered device uses less power than 8.0 W.

Because of line loss, the power received by the powered device can be less than the power available at the PoE port. Table 10 shows the maximum power available at a PoE port and the resulting power guaranteed to the powered device.

Table 10: Maximum Power per Port in Static Mode

Switch or Line Card

Maximum Power Delivered by PoE Port

Guaranteed Power to Powered Devices

EX2200 switches, EX3300 switches, EX4200 PX model switches, EX4300 P model switches, and EX4600 switches operating in a mixed Virtual Chassis

30 W

25.5 W

EX4300-48MP

30 W in two-pair mode

60 W in four-pair mode (high power)

95 W in four-pair mode (ultra-high power)

25.5 W

51 W

71 W

EX3200 switches and EX4200 P and T model switches running Junos OS Release 10.4 or earlier

15.4 W

12.95 W

EX3200 switches and EX4200 P and T model switches running Junos OS Release 11.1 or later

18.6 W

Note: Switches that are upgraded to Junos OS Release 11.1 from a previous release require an upgrade of the PoE controller software to obtain 18.6 W.

15.64 W

EX2300 and EX3400 switches

30 W

25.5 W

EX6200-48P line cards

30 W

25.5 W

EX8200-2XS-40P line cards and EX8200-48PL line cards

30 W (ports 0 through 11)

15.4 W (remaining PoE ports)

25.5 W

12.95 W

LLDP Power Negotiation

Link Layer Discovery Protocol (LLDP) power negotiation enables the PoE controller to dynamically allocate power to LLDP-enabled powered devices based on their power needs. The PoE controller allocates to an interface only the power currently required by the connected powered device, plus some additional power guard to accommodate cable length. This additional allocated power is approximately 15 percent of the requested value and it can allocate the power in small increments. For devices that use LLDP power negotiation, the power reserved for the interface is always greater than the LLDP-requested power value by the external POE device.

When the management option for PoE is set to class and LLDP is enabled (both are default settings), LLDP power negotiation is enabled by default. If you disable LLDP power negotiation or the powered device does not support it, the switch uses the class of the powered device to determine the maximum power for interfaces.

Note

Starting in Junos OS Release 18.1R1, on EX2300 and EX3400 switches, once power is allocated based on LLDP power negotiation, LLDP power negotiation remains in effect, even if the interface link status goes off and on, or if the LLDP configuration is changed.

Note

LLDP power negotiation is not supported on EX3200 and EX4200 (except EX4200 PX models) switches.

PoE Power Budget

The PoE power budget is the total amount of power that the PoE controller has available to allocate to its PoE ports. The PoE controller cannot exceed its PoE power budget and does not allocate power to a PoE port if the allocation would exceed the PoE power budget.

How the PoE power budget is determined depends how the PoE interface power allocation is determined.

In the class PoE management mode:

  • The power budget calculation for class 0 and class 4 powered devices, whose power allocation is based solely upon class, is based on actual power consumption. These values are displayed in the Power consumption field in the output of the show poe interface CLI command. The power budget is the sum of the power consumption values for all PoE-enabled interfaces.

    Note

    For Junos OS Releases 12.2R1 through 12.2R5 and 12.3R1 though 12.3R4, the PoE power budget for class 4 devices is based on maximum power.

  • The power budget calculation for class 1, class 2 and class 3 powered devices is based on the maximum power for the class. See Table 9 for the maximum power values by class. The maximum power for an interface is displayed in the Max power field in the output of the show poe interface CLI command. The power budget is the sum of the maximum power values for all PoE-enabled interfaces.

In static PoE management mode, the power budget calculation is based on maximum configured power. The maximum power for an interface is displayed in the Max power field in the output of the show poe interface CLI command. The power budget is the sum of the maximum power values for all PoE-enabled and statically configured interfaces.

In LLDP power negotiation mode, the power budget calculation is based on requested and negotiated power value, plus approximately 15 percent more. The maximum power for an interface is displayed in the Max power field in the output of the show poe interface CLI command. The power budget is the sum of the maximum power values for all PoE-enabled interfaces. In the case of LLDP power-negotiated devices, the total power consumption shown in the output of show poe controller is always less than the actual POE power budget.

PoE Interface Power Priority

You can configure a PoE interface to have a power priority. The power priority determines which interfaces receive power if PoE power demands are greater than the maximum PoE power consumption. If the total power allocated for all interfaces exceeds the maximum PoE power consumption, PoE power to lower-priority interfaces is turned off and the power allocated to those interfaces drops to 0. Thus you must set interfaces that connect to critical 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.

For EX6200 and EX8200 switches, interface power priority determines the relative priority of the interfaces on a line card, not on the switch as a whole. The relative priority of interfaces residing on different line cards is determined by line card priority. For example, if line card 1 has a higher power priority than line card 2 and a power shortage occurs, power is removed from the PoE interfaces in this order:

  • Low-priority interfaces on line card 2

  • High-priority interfaces on line card 2

  • Low-priority interfaces on line card 1

  • High-priority interfaces on line card 1

You can manually configure PoE interface power priority, or you can enable LLDP power priority, which assigns each interface the power priority provided by the connected LLDP-enabled powered device. Table 11 describes how the switch converts LLDP power priorities to switch power priorities.

Table 11: LLDP Power Priority Conversion to Switch Power Priority

LLDP Power Priority

Switch Power Priority

Critical, High

High

Low

Low

Note

LLDP power priority requires LLDP power negotiation to be enabled, which is enabled by default when the PoE management option is set to class.

Note

LLDP power priority is not supported on EX3200 and EX4200 (except EX4200 PX model) switches.

Release History Table
Release
Description
On EX4300-48MP switches, starting in Junos OS Release 18.2R1, Juniper Networks supports an extension to the IEEE 802.3at PoE+ standard that provides up to 95 W of power switches by increasing the number of wires carrying the power, utilizing all four pairs of wire in a standard RJ-45 Ethernet cable.
Starting in Junos OS Release 18.1R1, on EX2300 and EX3400 switches, once power is allocated based on LLDP power negotiation, LLDP power negotiation remains in effect, even if the interface link status goes off and on, or if the LLDP configuration is changed.
Starting with Junos OS Release 12.2R1, PoE commands are enabled on all non-PoE-capable EX2200 switch models.
Starting with Junos OS Release 18.1R2, PoE is supported on EX2300-24MP and EX2300-48MP switch models, including multigigabit interfaces.