Since the title is rather vague, this is the start of a series about building a TCP/IP and Ethernet framing stack from scratch for a microcontroller. The author uses a chip (W5100) which can handle TCP/IP itself, but also supports handing it pre-built Ethernet frames, although the chip handles the preamble and CRC calculation. Most of the article is about trying to communicate with the chip itself, and sending a test packet (which I'm guessing is hardcoded, although it's not called out in the article).
(I was hoping it would be about bit-banging Ethernet on some improbable bit of hardware.)
(I was hoping it would be about bit-banging Ethernet on some improbable bit of hardware.)