This article explains a scenario where an EX4100 switch is unable to provide sufficient power for an AP45, resulting in PoE compliance alerts in Mist. We clarify why this occurs and what it means for device functionality.

• PoE compliance alerts: Access Points report insufficient switch power.
• Access Point warnings: APs operate with reduced functionality.
• Service level events: Low Power.

On this scenario we have 2 AP45 devices connected via ge-0/0/0 and ge-0/0/1 on a EX4100-48P which are requesting 29.3 W, which is required since the AP45 needs 802.3bt for full Wi‑Fi functionality. However, the switch is only allocating 25 W. Below are outputs and stats from both APs:

AP1

Stats from AP1

  "power_needed": 29300 >>> Power needed.
    "lldp_stats": {
            "port_desc": "ge-0/0/0",
            "port_id": "ge-0/0/0",
            "ap_port_name": "",
            "lldp_med_supported": true,
            "power_request_count": 1,
          "power_allocated": 25500 >>> Power allocated by the swicth.
            "power_requested": 25500,
          "power_draw": 29300 >>> Power consumed.

AP2

Stats from AP2

  "power_needed": 29300 >>> Power needed.

   "lldp_stats": {

           "port_desc": "ge-0/0/1",

           "port_id": "ge-0/0/1",

           "ap_port_name": "",

           "lldp_med_supported": true,

           "power_request_count": 5,

           "power_allocated": 25500 >>> Power allocated by the swicth.

           "power_requested": 25500,

           "power_draw": 29300 >>> Power consumed.

As mentioned before, the AP45 requires 802.3bt for full functionality. Unfortunately, only the multigigabit (MP) models of the EX4100 switch support 802.3bt mode, while the gigabit models do not. You can verify this in the Feature Explorer:

https://apps.juniper.net/feature-explorer/feature/3401?fn=Power%20over%20Ethernet%20IEEE%20802.3bt

Also confirm the POE version of the platform on the Juniper documentation:

https://www.juniper.net/documentation/us/en/software/junos/poe/topics/concept/poe-overview.html#:~:text=EX4100%20gigabit%20switch%20models%20models

On 802.3at it has dynamic functionality based on what is configured. The AP will do 4×4 on any two data radios, or 2×2 on 2.4 GHz, 4×4 on 5 GHz, and 2×2 on 6 GHz with three data radios enabled. For example:

• If your WLAN configuration only has two bands configured, the AP will operate as 4×4 on both of the data radios.
• If WLAN configuration has three bands configured, which means all three data radios are active, then the AP will operate as 2×2 on 2.4 GHz, 4×4 on 5 GHz, and 2×2 on 6 GHz

The EX4100 gigabit switch models support up to 30 W per port (802.3at mode); however, only 25.5 W is guaranteed to powered devices:

https://www.juniper.net/documentation/us/en/software/junos/poe/topics/concept/poe-overview.html#:~:text=EX4100%20gigabit%20switch%20models%20models

This matches the power allocated to the APs according to the AP stats, as well as the PoE outputs reported by the switch:

root@user show poe interface 
Interface    Admin       Oper    Pair/Mode  Max        Priority       Power          Class
             status      status  status     power                     consumption    
ge-0/0/0    Enabled      ON     2P/AT      25.5W(L)   High           10.5W           4
ge-0/0/1    Enabled      ON     2P/AT      25.5W(L)   High           10.8W           4

NOTE: Power Class 4 in Power over Ethernet (PoE) refers to a specific classification within the IEEE 802.3at (PoE+) standard, designed to deliver higher power than basic PoE. It signifies that a device requires more power than standard devices, generally requiring up to 30W from the source (PSE).

For more information, you can review the AP45 documentation, specifically the "Power Options" section:

https://www.juniper.net/content/dam/www/assets/datasheets/us/en/access-points/ap45-datasheet.pdf

During the boot‑up LLDP process, the AP negotiates its power requirements (802.3at/bt). Therefore, it is not possible to “pin” or trick the AP into believing a specific power mode is being supplied by the switch. One possible workaround is to use external "PoE injectors", which can provide power independently of the switch’s PoE configuration.