The Open Lighting Architecture is a software framework for distributing lighting control information. It can run as a standalone service and convert between protocols or be used via the client APIs.
OLA runs on a many different platforms including ARM, which makes it a perfect fit for low cost Ethernet to DMX gateways.
A step-by-step tutorial is available on installing OLA on a Raspberry Pi.
With the right hardware, you can be running OLA within minutes.
The Raspberry Pi has an SPI output so it can drive LED pixels directly. The OLA LED Pixel tutorial covers controlling pixel strings using OLA on a Pi.