Description

This article describes PoE (Power over Ethernet) on an SRX device.

Symptoms

The problem is that power is not being supplied by some interfaces to the devices connected to the interfaces.

The goal is for the interfaces to supply power to the devices connected to the interfaces.

Solution

The cause of the power problem is revealed in the scenario below.

An SRX240H-POE device, by default, can supply a maximum 150W of power to each interface.

This is verified by the command and output below:

admin@POE# run show poe controller
Controller Maximum Power Guard band Management
index power consumption
0 150.0 W 27.5 W 0 W Static

Each interface, in turn, supplies power to the devices connected to it.

As shown in the example below, 15 devices are connected to an SRX240H-POE, but only nine are able to get power:

admin@POE# run show poe interface
Interface Admin status Oper status Max power Priority Power consumption Class
ge-0/0/0 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/1 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/2 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/3 Enabled Powered-up 15.4W Low 5.0W 2
ge-0/0/4 Enabled Powered-up 15.4W Low 2.2W 1
ge-0/0/5 Enabled Powered-up 15.4W Low 1.8W 1
ge-0/0/6 Enabled Powered-up 15.4W Low 2.1W 1
ge-0/0/7 Enabled Powered-up 15.4W Low 2.1W 1
ge-0/0/8 Enabled Powered-up 15.4W Low 5.6W 2
ge-0/0/9 Enabled Powered-up 15.4W Low 5.1W 2
ge-0/0/10 Enabled Powered-up 15.4W Low 2.1W 1
ge-0/0/11 Enabled Powered-up 15.4W Low 1.8W 1
ge-0/0/12 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/13 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/14 Enabled Searching 15.4W Low 0.0W 0
ge-0/0/15 Enabled Searching 15.4W Low 0.0W 0

The interfaces that have a Powered-up status (ge-0/0/3 through ge-0/0/11) are able to supply power to the devices connected to them. The interfaces that have a Searching status (ge-0/0/0 through ge-0/0/02, and ge-0/0/12 through ge-0/0/15) are unable to supply power to devices connected to them.

The ge-0/0/4 interface, for example, is given 15.4W of power by the SRX, but the interface is providing only 2.2W of power to the device connected to it.

As nine ports have powered on the devices connected to them, the SRX is already providing 15.4W*9 = 138.6W of power to its interfaces. That means the SRX is left with just 150-138.6 = 11.4W of power, which is less than the power called for by the default behavior (15.4W to an interface). This shortfall leaves the other six ports searching for the required power

The solution is to override the default behavior.

There are two ways to override the behavior: static or dynamic allocation of Max power to an interface.

Static allocation of Max power to an interface:

# set poe interface ge-0/0/12 maximum-power 10


Dynamic allocation of Max power to an interface:

This is dependant on the consumption class of the connected device. Based on the class of the connected device, SRX automatically determines the maximum amount of power given to an interface.

You can also set the maximum amount of power given to an interface using the command below:

# set poe management class

The table below shows the class of powered devices and their required power levels.

Power Consumption Table

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