I have four Raspberry Pi model 4B boards and a Raspberry Pi model 3B+
board and would like to know whether or not Power over Ethernet (PoE) is
supported by the Pi9 port.

Has anyone attempted to power a Plan9 cluster/grid over PoE? What PoE
network switches would you recommend? Were there any issues? Richard
Miller?

To be clear, a PoE network enables boards to be powered over an Ethernet
network if a side-board (HAT) is connected. [1] A PoE network switch
conforming to IEEE 802.3af delivers power through the each Pi's RJ45
network connector over Cat 5 cabling. [2]

To my knowledge, neither the 9front kernel sources nor the documented
list of supported hardware, specifically mentions PoE. [3] It seems the
network switch and HAT negotiate power delivery independently of the
kernel so I cannot think of a reason why Plan9 would not support
powering this way.

References
[1]: https://www.raspberrypi.org/blog/introducing-power-over-ethernet-poe-hat/
[2]: https://ieeexplore.ieee.org/document/1213877
[3]: https://9p.io/wiki/plan9/Supported_PC_hardware/index.html

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Barry Wasdell (bwasd)