[EX] LLDP-POE negotiation fails when POE device requests 25.5W through LLDP

Summary:

This article explains the behavior of EX Series devices when a Power over Ethernet (PoE) device requests 25.5W through Link Layer Data Protocol (LLDP). It clarifies that upgrading to a Junos OS version that fixes the issue is the only way to resolve the problem of PoE devices not working as expected when they request 25.5W of power through LLDP.

Symptoms:

Consider that an Aruba AP-205H is connected to a PoE interface and is trying to negotiate power through LLDP, for example.

{master:0}[edit]
root@EX2200# show
interfaces {
    ge-0/0/22 {
        unit 0 {
            family ethernet-switching;
        }
    }
protocols {
    lldp {
        transmit-delay 1;
        interface all;
    }
    lldp-med {
        interface all;
    }
}                                     
poe {
    lldp-priority;
    interface all;
}

root> show poe interface ge-0/0/22 
PoE interface status:
PoE interface                : ge-0/0/22
Administrative status        : Enabled
Operational status           :   ON
Power limit on the interface : 30.0W    <<< No negotiation of power through LLDP.
Priority                     : Low
Power consumed               : 7.9W
Class of power device        :        4
PoE Mode                     :   802.3at

It is seen that the negotiation of power through LLDP is not made and therefore, the requested 25.5W of power is not allocated.

Further, the following observations were also made in the test environment:

When an Aruba AP-205H device is connected to the PoE interface of an EX2200 Series device, for example, and the Aruba TLVs begin requesting 25.5 Watts of power, they never receive any PSE allocated power.
When an Aruba AP-315 device is connected to the same PoE interface of the EX2200 Series device, and the AP-315 device requests 20.8 Watts of power, it is allocated the 20.8 Watts of power, which begins a successful PoE allocation by using LLDP-MED.

Cause:

The above explained issue may be seen on Juniper EX series devices.

Solution:

The issue has been fixed in the following Junos OS releases: Junos OS release 12.3R12-S13, 12.3R13, 14.1X53-D51, 15.1R7-S5, 15.1R8, 15.1X53-D59, and 17.1R3-S1.

After upgrading to any of the above Junos OS versions, LLDP power is negotiated successfully when requests are made for 25.5W and more units of power.

---------------------------------
root@EX2200# run show poe interface

ge-0/0/21    Enabled     OFF     15.4W      Low            0.0W           not-applicable
ge-0/0/22    Enabled      ON     25.5W(L)   Low(L)         8.1W            4  <<< Negotiation of power through LLDP is successful
ge-0/0/23    Enabled     OFF     15.4W      Low            0.0W           not-applicable

(L) LLDP-negotiated value on the port.

root> show poe interface ge-0/0/22 

PoE interface status:
PoE interface                : ge-0/0/22
Administrative status        : Enabled
Operational status           :   ON
Power limit on the interface : 25.5W (L)     <<<<<  Negotiation of power through LLDP successful
Priority                     : Low (L)
Power consumed               : 7.9W
Class of power device        :        4
PoE Mode                     :   802.3at

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