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?

The 5-hour Reliability Theory: Networking through a Systems Analysis Lens webinar by Rachel Traylor is now available without a valid ipSpace.net account. Enjoy!

To watch more free ipSpace.net videos, browse them here, or click the Access Free Content button in any webinar roadmap.

netlab release 26.09 added support for Syslog clients and servers. We implemented the clients on numerous platforms; the only Syslog server implementation is the dnsmasq container.

Adding Syslog to a netlab lab is (almost) trivial:

• You have to (re)build the dnsmasq container with the netlab clab build dnsmasq command to add rsyslogd to the container image
• When you add a dnsmasq node to a lab, it automatically starts a Syslog server
• The Syslog client is enabled on other nodes (or globally) with the services.syslog.server setting.

The OSPF is stuck in database exchange state symptom is probably familiar to every networking engineer who ever had to pass a certification exam. It’s caused by the MTU mismatch between adjacent OSPF routers.

The recent (unexpected) trip into the how crazy is it to declare your interface MTU to be zero wonderland uncovered way more than I ever wanted to know about this arcane topic. Here are a few highlights (thanks a million to Aleksey Popov for researching this topic and posting information here, here, and here).

After a long journey, we finally we got to the final scenario in my ITNOG10 Segment Routing workshop: EVPN services over an SR-MPLS core.

I used the same lab topology as in the previous services-focused scenarios blog post, replacing two PE-to-host subnets with a stretched VLAN.