Low Power Mode

Overview

When connecting a Cisco Meraki access point (AP) to different PoE switch models, sometimes you may run into an insufficient power scenario. This is called a Low Power Mode.

Some Meraki MR access points require PoE+ or PoE++ power levels to perform and offer all features and functionality. However, some switches and PoE injectors may not be able to supply or negotiate these energy levels. If the MR is receiving less power than PoE+ (802.3at), it will display "running in low power mode."  The same situation may happen with an MR that requires PoE++ (802.3bt) Power level but the switch or power injector is unable to provide or negotiate higher power levels.

PoE Standards

As a general best practice, you should do the following two actions when planing and implementing your AP and switch:

1.  Check your AP and Switch datasheets and make sure they are compliant to the same or compatible standards.
2. Enable both CDP and LLDP in the switch Ethernet ports connected to your AP; doing this will allow best compatibility and energy control

Low Power Mode scenarios

1. Cisco Meraki switch family (MS) have both CDP and LLDP enabled by default just like Cisco Meraki MR access points. There wouldn't be any issue requesting power when connecting MR and MS together, unless your MS doesn't have enough Power Budget to provide energy to your MR.
2. When connected to other vendor switches (e.g.: HP ProCurve switches), your AP would use MDI detection during boot up and LLDP when negotiating any PoE Energy levels.
   • If your AP is PoE+ compliant and it is connected to a switch port that has LLDP disabled or the switch itself is Legacy PoE, then your AP would get in Low Power Mode scenario.
   • Likewise, if your AP is PoE++ compliant and it is connected to an Ethernet switch port that has LLDP disabled or the switch itself is PoE+ only, then your AP would fallback to PoE+ and display an alert in the dashboard saying “Access point is running in low power mode”.
3. When connected to Cisco switches (e.g.: Catalyst), AP can use CDP or LLDP to request PoE Energy levels within PoE and PoE+. In this case, AP would use CDP primarily and LLDP additionally as per PoE+ requirement. There are some situations where CDP alone isn't enough to request PoE+ energy levels. In addition, MR APs must use both CDP and LLDP to request Energy levels within PoE++ levels.

Impact of Low Power Mode

While in low power mode, the MR will disable its Air Marshal radio as well as some of its transmit streams on the 2.4 GHz band. Despite being in low power mode, the device can still supply full 802.11ac capabilities. 

Models with a dedicated scanning radio, such as the MR18/32/34/42/52/53/84, don't generate channel_scan events. They rely on the scanning radio to get the neighbor and channel utilization report on an ongoing basis.

In comparison, models without the dedicated scanning radio, such as the MR12/16/20/24/70, scan the whole spectrum every 2 hours when there are no clients associated. When low power mode is enabled the scanning radio function becomes disabled. Thus, not only are there no channel_scan events but AutoRF channel assignment can be negatively impacted.

Troubleshooting

If the device is running in low power mode, ensure that the power source supports the 802.3at power standard and that it is supplying full power to the device. To identify if the AP is running in low power mode, navigate to the AP details page on the Meraki dashboard, found under Wireless > Monitor > Access Points. Once there, under Status there will be a field that indicates the Power source and if the AP is in low power mode.