Did such a thing - was fed by a garland of two hubs (Intel and D-Link).
The topology is this:
power supply <-> 100 meters ethernet <-> Hub <-> 100 meters <-> Hub
Food comes in two halves pairs (brown and blue) (white-brown white-blue +, blue -)
As a source of 48V is applied from the transformer dot-matrix printer Epson LX-300 (fits perfect), then the rectifier bridge and a capacitor.
At sampling points the power supplied Converter LM2576HV-ADJ, according to the standard scheme:
This scheme operates without comment.