Low power mode on Cisco 3850 switches

[Dave_Lewis]

Hello,

I recently deployed a number of MR42's connected to WS-C3850-48P running 3.07.05e and noticed they all came up in low power mode.

Interface Admin  Oper       Power   Device              Class Max
                            (Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Gi1/0/44  auto   on         15.4    MR42                4     30.0
Gi1/0/45  auto   on         15.4    MR42                4     30.0
Gi1/0/46  auto   on         15.4    MR42                4     30.0
Gi1/0/47  auto   on         15.4    MR42                4     30.0

I checked through doc 2068 on configuring Cisco switches but I already had LLDP running and didn't want to statically set power on the ports. 

I found the following command fixed the issue when entered on each interface connected to an AP:

power inline port 2-event

The APs immediately switched to full 802.3at (no reboot required):

Interface Admin  Oper       Power   Device              Class Max
                            (Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Gi1/0/44  auto   on         30.0    MR42                4     30.0
Gi1/0/45  auto   on         30.0    MR42                4     30.0
Gi1/0/46  auto   on         30.0    MR42                4     30.0
Gi1/0/47  auto   on         30.0    MR42                4     30.0

Just thought I'd share this in case anyone else comes across the same issue.

Dave

[PhilipDAth]

If you go:
Wireless/Access Points/[click on an access point]

Down the bottom it will say how much power it is actually using.

I just checked one of mine, and it has negotiated 802.3at (30W) but is only using 5W to 6W at the moment.  It is possible the 3850 was only giving 15W because the access point had not yet asked for more power.

[Dave_Lewis]

Hi,

Possibly yes but all of the APs on this site were showing as low power mode:

and as soon as I entered that command they all showed as 802.3at:

Interestingly we have other sites with 3850's that we haven't entered this command on. Only differences I can see are this:

Model Number	Hardware Version	Software Version	Needed 2-event?
WS-C3850-48P	V04			3.03.05SE		NO
WS-C3850-48P	V07			3.07.05E		YES

So next step would be to upgrade the V04 site to 3.07.05e to see if that changes anything but I haven't got spare time at the moment. Anyway, whatever the cause, just wanted to share to save people time if it happens to them.

Dave

[JaiminPatel]

Hi Guys,

PoE 802.3af means running in low power mode or PoE 802.3at?

I am using MR53 device. See my screenshot below... Mine doesn't say running low power mode.

[PhilipDAth]

Your's is working correctly.

[Chris_M]

@JaiminPatel

PoE 802.3af means PoE standard which goes up to 15 watts. PoE 802.3af is PoE+ which goes up to 30 watts. Devices that can use that much but knows it limited to 15 watts will say "low power mode". UPoE by Cisco goes up to 60 watts but not yet a defined standard.

[DrDray]

Hey @Dave_Lewis, check this out as well. Could just be the default config is stuck because of how the devices initially communicated with each other.

https://documentation.meraki.com/MR/Other_Topics/Low_Power_Mode_on_Cisco_Switches

Hope this helps!