Just a very quick reminder that if you power your CW AP using an incompatible 802.3at power injector, you will likely see the AP successfully boot up, but it disables its radios few seconds later. The result is no SSID put on the air.
What to look for in the logs?
If you console or SSH into the AP, you will see this error message. Followed by radio interfaces going down.
set_sys_cond_state: condition critical state 4
condition critical state 4 error message
That’s it. Use officially supported injectors, and save yourself from the trouble I ran into 😊
My Catalyst 9800-CL controller is hosted on a cloud, so I don’t need any hardware for that. Finally, my Catalyst 9136 Wi-Fi 6E AP is powered by a Catalyst 3560CX 10 Gigabit Ethernet multigigabit switch.
6 GHz 2×2 MIMO setup powered by PoE+
Catalyst 9136 is Cisco’s premium AP with all the bells and whistles including hexa-radio architecture and built-in environmental sensors for smart building use cases. It requires an 802.3bt/UPOE power source to enable 6 GHz radio in full performance 4×4 MIMO mode. The switch I use supports 802.3at/PoE+, which is great, but 6 GHz radio downshifts to 2×2. And that’s where an 802.3bt power injector comes to the rescue.
Since the Cisco injector isn’t widely available yet, I decided to test this Zyxel one. It provides 802.3bt power and allows the AP to run in full power and full 4×4 6 GHz radio mode with no compromise.
Do I like power injectors in production?
Absolutely not! Ideally you should design for 802.3bt/UPOE switches to power all your new APs via PoE.
It allows you to:
easily, centrally and remotely monitor how much power the APs use
enable/disable power on a port to bounce an AP
leverage redundant Platinum-rated power supplies for the AC to DC power conversion
manage the solution with ease – just think how difficult it is to manage more than 1 power injector, the number of AC power sockets, and what happens when someone disconnects the injector?
I still use C3650 UPOE mGig switch in my lab. Catalysts 9300 and 9400 the best choice these days.UPOE and mGig capable C3650 providing full power to the AP
Final look
Carrying a full-size switch is not really an option for me, because small form factor is my main goal. So a power injector works best for me. But if I could I would love to use a compact 802.3bt switch.
Are you wondering if the PoE splitter connected to my iperf3 server (the little black box with 3 Ethernet interfaces) actually negotiated 2.5 Gbps Full duplex with the switch? Yes, it did. But keep in mind that the PoE splitter is technically only rated for 1 GbE. So use as short patch cable as possible and ideally CAT6.
Still few things to tidy up and perhaps I could build this into a nice Pelican case
