Why would I want to look up ASNs via DNS in the first place? Time for a little recap: In 2025 I wrote a piece about the new layer-3-only datacenter network my team and I designed (and implemented) for my day job. A spine & leaf DC fabric usually means: one (private) ASN per device. That obviously includes spine and leaf switches but also hosts (bare metal and VMs), hypervisors, Kubernetes clusters and so on.

A recent episode of the (German) “Engineering Kiosk” Podcast with Sébastien Pahl about micro VMs reminded me that I played around with that technology a while ago and always wanted to blog about it - but never got round to it. So here we go! Being one of the maintainers of the Ganeti project I am naturally interested in all things virtualisation & hypervisors. A few years ago Firecracker caught my attention and while digging deeper I found out that QEMU has something similar, inspired by Firecracker. Spoiler: it never made it into Ganeti for various reasons, but a fun technology to play with nonetheless!

Earlier last year I wrote a piece about BGP unnumbered layer-3-only datacenter networks. Meanwhile that has been put into production and while it works great for regular hosts, we now want to explore how to use it with virtual machines. Specifically with VMs running on Ganeti clusters.

As one of the Ganeti maintainers, I’ve spent a fair bit of time in the network configuration code over the past weeks. With version 3.2 about to land - bringing the first meaningful changes to that part of the codebase in a while - this is a good moment to walk through the network modes Ganeti offers, their use cases, and the improvements landing in 3.2.

This blog post is neither meant to endorse nor to discourage the use of (generative) AI. I personally have very mixed feelings about this technology (from ecological to ethical to copyright / legal standpoints). But as with previous and recent turning points in IT, it is worth to at least get a grip on the technology involved to take informed decisions. Examples of such turning points would be the advent of systems automation with Ansible, Puppet, Saltstack and the like, the rise of Docker, Kubernetes or containerization in general and of course “the cloud”. You may not like it, but it also won’t go away from you not liking it.

Digital independence doesn’t have to be an “all or nothing” mission. During last year’s Chaos Communication Congress the “Digital Independence Day” was announced to the general public. Supported by various organisations, it tries to convince people to move away from platforms owned by Big Tech (e.g. WhatsApp, Amazon, Facebook and the like) and switch to alternatives. This addresses concerns about data privacy and sovereignty, as well as the dominance of US-based platforms. It does not necessarily mean to self-host everything on cheap virtual machines or at home. In this blog post I will try to give an overview of services I use or run by myself (and why I choose them).

It started with a simple idea: what if everything in our data center was routed - not just the core-routers and -switches, but the access layer and the hosts too? So that’s exactly what we did. No VXLAN, no EVPN, no fancy overlays - just plain Layer 3.

A while ago our landlord got our old gas heater replaced with a newer gas condensing heating system (specifically a Bosch GC7000F). Unexpectedly it came along with a voucher for a free Bosch internet gateway (Bosch Connect-Key K 30 RF). Even more unexpectedly I received the gateway only a few weeks after registering online. However, that turned out to be sort of a bummer quite quickly. In short: this gateway has no local endpoint whatsoever and only submits data encrypted to Bosch systems. You may access the data through their HomeCom app (iOS, Android) but that’s about it. Their support has confirmed there are no immediate plans to changes this. Some more information can be found in this Github issue.

A while ago my work team was assigned the task to migrate one firewall generator into a different one. Output were iptables rules for Linux servers in both cases. As we wanted to ensure a smooth transition, we were looking for a way to actually test the new rulesets before being deployed into production. A little bit of googling did not yield any results, so we came up with our own solution.

Recently, I stumbled across this brilliant Mastodon thread about 50 things to do with a software defined radio (SDR) by @blinry. Specifically this Toot about utility meters and Wireless M-Bus got me thinking about my own water meter. It is a rather recent model with a digital display and the display also shows a little RF symbol! I never put much thought into that, but seeing how it easy it might be to aquire data from the meter I thought I should give it a try.