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.

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?

Last week’s SwiNOG was (as expected) great fun at a phenomenal location, starting with the first slide of the first presentation: “6 Stages of Network De-sh*tification”. I particularly loved the “talk less, chat more” schedule. The longer breaks gave us plenty of time to catch up with old friends and discuss interesting, sometimes completely unexpected, topics. For example, I learned that SIP MESSAGE is used to carry SMS messages these days.

As much as I loved chatting with fellow networking engineers, I also found these presentations highly interesting:

At ITNOG 10, I’ve seen something that I haven’t seen in a very long time: a mini-Interop-style physical lab using a dozen devices from different vendors. The network core was a leaf-and-spine fabric with off-path BGP route reflectors and numerous other devices attached to it.

I’ve configured a few networks in the past, so I know it must have been a beast to configure all those devices by hand (and fix all the IP addressing errors), but then a thought struck me: unless one wants to practice configuring IP addresses, it might be a good idea to use netlab to generate the IP addressing plan and partial device configurations.

Naveen Kumar Devaraj was reading my Integrated Routing and Bridging (IRB) with EVPN MAC-VRF Instances lab exercise and spotted this detail:

Arista EOS originates MAC-IP routes with and without IP addresses, effectively doubling the size of the EVPN BGP table

He kindly wrote a LinkedIn comment explaining that behavior:

@sjhloco wrote an excellent in-depth description of how you can use containerlab and netlab to manage your labs as code.

He also documented a few netlab shortcomings (one of which caused a crash); fortunately, I found his blog post (admittedly over a year later) and fixed most of them in release 26.04: