The early October 2021 Facebook outage generated a predictable phenomenon – couch epidemiologists became experts in little-known Bridging the Gap Protocol (BGP), including its Introvert and Extrovert variants. Unfortunately, I also witnessed several unexpected trips to Mount Stupid by people who should have known better.

To set the record straight: everyone’s been there, and the more vocal you tend to be on social media (including mailing lists), the more probable it is that you’ll take a wrong turn and end there. What matters is how gracefully you descend and what you’ve learned on the way back.

When I started creating the How Networks Really Work series, I wondered whether our subscribers (mostly seasoned networking engineers) would find it useful. Turns out at least some of them do; this is what a long-time subscriber sent me:

How Networks Really Work is great, it’s like looking from a plane and seeing how all the roads are connected to each other. I know networking just enough to design and manage a corporate network, but there are many things I have learned, used and forgotten along the way.

So, getting a broad vision helps me remember why I chose something and maybe solve my bad choices. There are many things that I may never use, but with the movement of all things in the cloud it’s great to know, or at least understand, how things really work.

Two weeks ago I replied to a battle-scar reaction to 7-layer OSI model, this time I’ll address a much more nuanced view from Russ White. Please read his article first (as always, it’s well worth reading) and when you come back we’ll focus on this claim:

The OSI Model does not accurately describe networks.

Like with any tool in your toolbox, you can view the 7-layer OSI model in a number of ways. In the case of OSI model, it can be used:

I should have known better, but I got pulled into another stretched VLANs for disaster recovery tweetfest. Surprisingly, most of the tweets were along the lines of you really shouldn’t be doing that and that would never work well, but then I guess I was only exposed to a small curated bubble of common sense… until this gem appeared in my timeline:

Interestingly, that’s exactly how IP works:

One of my readers sent me this interesting question:

It begs the question in how far graduated students with a degree in computer science or applied IT infrastructure courses (on university or college level or equivalent) are actually aware of networking fundamentals. I work for a vendor independent networking firm and a lot of my new colleagues are college graduates. Positively, they are very well versed in automation, scripting and other programming skills, but I never asked them what actually happens when a packet traverses a network. I wonder what the result would be…

I can tell you what the result would be in my days: blank stares and confusion. I “enjoyed” a half-year course in computer networking that focused exclusively on history of networking and academic view of layering, and whatever I know about networking I learned after finishing my studies.

I was speaking with a participant of an SDN event in Zurich after the presentations, and he made an interesting comment: whenever he experienced serious troubleshooting problems in his career, it was due to lack of understanding of networking fundamentals.

Let me give you a few examples: Do you know how ARP works? What is proxy ARP? How does TCP offload work and why is it useful? What is an Ethernet collision and when would you see one? Why do we need MLD in IPv6 neighbor discovery?

FRRouting release 10.6 promised “BGP IPv6 VTEP support,” claiming “it enables EVPN deployments using IPv6 tunnel endpoints while maintaining full backward compatibility with IPv4 VTEPs.” Of course, I had to try it out, and since we already have EVPN over IPv6 running on Arista EOS (since netlab release 26.01), I decided to set up a simple lab with an Arista cEOS device running release 4.35.2F and the latest FRRouting container.

I was not exactly surprised when it did not work. While Arista accepted FRRouting EVPN routes, the FRRouting BGP daemon rejected routes sent by Arista EOS:

In a recent article, Scott Alexander made an interesting point: What AI produces are not hallucinations but shameless guesses (also known as bullshit) because the training process rewards the correct answers but does not penalize the incorrect ones. After all, having an AI model say, “I don’t know that” is not good for business, is it?

On a tangential note, calling those blunders hallucinations was a marketing masterstroke. Not being a native English speaker, I might be missing some nuances, but I feel like hallucinations might be something you’re not responsible for (some of the time), whereas we all know who’s responsible for bullshit and shameless guesses – and responsibility is something the AI companies are clearly trying to stay as far away from as possible.

On another tangential note, if you’re not following Scott Alexander’s blog substack, you’re missing out.

IS-IS was designed to carry node addresses (NSAPs) between level-1 routers (called Intermediate Systems) within an area and area prefixes between level-2 routers, resulting in a perfect separation of concerns and forwarding information summarization. When IETF tried to use the same routing protocol for a networking stack with a completely different addressing mentality, something had to give.

A year ago, I was complaining about SR Linux breaking its configuration data model with a new software release. At that time, I was promised it would only happen once a year, and, like clockwork, that moment arrived with the SR Linux release 26.03.

However, this year Miguel Redondo fixed the netlab SR Linux configuration templates (VRF export policies, LocPref routing policy changes) before I could even start looking at them, and Roman Dodin released a tool that tells you exactly what changed between software releases and how to fix it.