USB-Ethernet Adaptors and Power over Ethernet (PoE)
I have a LeMaker HiKey and I'm having trouble getting the network running in a preferred configuration. The HiKey is an inexpensive ARM64 development board running Linaro. Linaro is a lot like Debian with an LXDE desktop, and in effect, this is a mini-desktop with an ARM CPU architecture.
The board is powered and has two USB ports and a micro USB port. However, the board lacks an ethernet port. The USB ports do not power attached devices, so I need to use a powered hub when using them.
If I use an Ethernet-to-USB adapter with a powered hub, then the device has network connectivity. If I remove the powered hub and provide Power over Ethernet (PoE+) to the Ethernet-to-USB adapter, then the device loses its network connectivity.
I tried 3 different Ethernet-to-USB adapters with the same results, so I am missing something. I think this is a case of me not knowing what I don't know. Can anyone explain to me what I am missing in the configuration using Power over Ethernet?
(I am trying to avoid a PoE injector in the adapter. That is, I don't want to have to plug the Ethernet-to-USB adapter into a wall socket. Its the reason I purchased a Power over Ethernet switch).
142 Answers
For PoE to work, both ends of the Ethernet link carrying power need to support the same flavor of PoE. I've never seen a USB Ethernet adapter that supports receiving (acting as the "powered device" (PD), not the power supply for) any flavor of PoE.
I doubt a PoE-receiving USB Ethernet adapter exists, because PoE is thought of as a way to power whole remote embedded devices, not just their NICs, and I don't think there's a commonly implemented way for a USB device to power a USB host (not until USB type-C, that is).
So you won't be able to make this work until/unless you find a USB Ethernet dongle that is designed to act as a PoE receiver for the same flavor of PoE as your PoE-supplying hub/switch/midspan power supply (power injector/splitter) supplies.
2I've been looking for a similar device that would let me do this without an ethernet adapter, a PoE usb splitter and a Y-cable and this is the closest I've found so far. It uses USB-OTG to connect the ethernet adapter directly to the device while also providing power.
And a similar solution for USB-C+PD:
