Networking

While troubleshooting a wireless issue, I mentioned offhand to another engineer that a particular MAC address was private. They immediately asked me “How did you know just by looking at it?” I said “Look at the second least significant bit of the most significant byte,” but quickly realized that needed a bit more explanation. “Private” MAC addresses, at least as implemented by Apple and Android, sets the locally-administered bit for their randomized addresses. RFC7042 section 2.1 specifies the “Local bit”: ...

The Problem A common issue with infrastructure as code, is that it is often possible for someone to go in after deployment and manually change things. I still want to preserve the ability for the infrastructure folks to go in and make emergency changes, but I also want to discourage this practice as much as possible. To this end, I’ve been using a pattern where any “out of band” changes are alerted to the rest of the team. That way, everyone can be aware there was a change made, and can go back afterwards and follow the standard procedures for the change. ...