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?

A reader asked how he could access the Routing in EVPN Fabrics videos, and the simplest thing for me to do was to make all the videos in the EVPN webinar public. Almost twelve hours of EVPN goodness is waiting for you.

You probably noticed that I always ask AI to generate some weird image to go with the “free videos” blog posts. This time, ChatGPT made an extra comment ;)

TL&DR: Third time is (supposedly) a charm. Not in this case.

It’s a bit hard to understand why one would launch an enterprise data-center-grade network operating system without candidate/active configuration in the 21st century, but that’s what Cisco and Arista did with Nexus OS and EOS. Arista fixed that omission with configuration sessions more than a decade ago¹. It took Cisco a bit longer.

The first attempt was the so-called two-stage configuration commit, which is functionally almost identical to the Cisco IOS XR “candidate” configuration:

I was reading the nice BGP Multi-Homed with Two ISPs and Two Routers scenario by Suresh Vinasiththamby - Packetswitch and thought wouldn’t it be nice if he were using netlab to build the lab, as that would give you the opportunity to build the same lab with zero hassle using non-Cisco devices. Guess what – Suresh already did just that. I was so glad to see someone using netlab in just the way I imagined it to be used.

A Packet Pushers newsletter brought me a link to a fantastic CLI tool: octomon by Simon Thorpe. Not only does it look awesome for a CLI tool, but it’s also one of those things always worth having in your toolbox, because you never know when you’ll need it.

Thanks a million, Ethan and Drew, for collecting the nuggets for us.