Tag: Network

With Fast Ethernet, Ethernet introduced something new. Previously, the Physical Signaling layer was integrated into the MAC and connected to the actual media through a Media Attachment Unit. While the user could switch between twisted pair (10Base-T), thinnet (10Base2), thicknet (10Base5), or even fiber (10Base-F) simply by changing MAUs, switching to a different encoding (e.g. Fast Ethernet) would require a completely new interface.

Instead of requiring new networking equipment to manage the PCS of each individual protocol, the MAC communicates with the PHY with a Media Independent Interface (MII). Now, free of protocol-specific encodings, different line rates and protocols could be selected by simply switching between different PHYs, leaving the MAC unaffected. While interchangeable PHYs is now the domain of high-end networking (e.g. SFP modules), the MII interface and its derivatives are the primary mechanism for connecting integrated MACs (and FPGAs) to commodity Ethernet transceivers.

Much of my recent professional development has focused on Ethernet, making it a convenient target for technical essays. Unlike much of the Internet, this series of essays will focus on practical implementation of Ethernet from an FPGA or ASIC perspective. This means the necessary waveforms and encodings to generate ethernet packets when directly connected to a PHY or medium.

The essays will be making extensive references to IEEE 802.3-2022 and every effort will be made to specify the exact clauses for further research by the reader. I will not be using the amendment names (e.g. 802.3z for Gigabit Ethernet) because they are not not useful for finding content within the actual standard and any given clause may have been modified by multiple amendments.

When using FreeBSD, the most common method for virtualization and process isolation are jails. Introduced with FreeBSD 4.0 in March of 2000, they predate the closest Linux equivalent, cgroups (and, by extension, Docker), by nearly a decade.

A core part of any virtualization technology is its interaction with the networking infrastructure. In this regard, I’ve found much of the available documentation lacking, often deferring to third party tools which are no longer maintained. As such, I’ve had to scrape multiple sources and reverse engineer system programs to figure out how it’s put together.

In the modern world, people tend to use massive frameworks to accomplish simple tasks. Nothing quite like swatting a fly with a nuclear missile when you load up 100 megs of runtime just to execute ping and post the result to a database. But sometimes, when you’re writing a utility, you want it to be quick and lightweight. And if you’re going through the effort, you might as well see about making it portable.

Recently, I needed to hack together a quick server-side application for a test page. When it comes to quick and dirty, most people turn to Python. While Python is hardly my favorite language, it is certainly suited for the task.

One of my requirements was that I wanted to minimize the number of dependencies. Installing Python is bad enough (my nginx container is extremely bare bones), but installing a massive framework for what was effectively a wrapper around a system command would make things even worse. So I decided to make due with wsgiref.simple_server that ships with CPython.