A little while ago I explained why you can’t use more than 4K VXLAN segments on a ToR switch (at least with most ASICs out there). Does that mean that you’re limited to a total of 4K virtual ethernet segments?

Of course not.

You could implement overlay virtual networks in software (on hypervisors or container hosts), although even there the enterprise products rarely give you more than a few thousand logical switches (to use NSX terminology)… but that’s a product, not technology limitation. Large public cloud providers use the same (or similar) technology to run gazillions of tenant segments.

Listening to public cloud evangelists and marketing departments of vendors selling over-the-cloud networking solutions or multi-cloud orchestration systems, you could start to believe that migrating your workload to a public cloud would solve all your problems… and if you’re gullible enough to listen to them, you’ll get the results you deserve.

Unfortunately, nothing can change the fundamental laws of physics, networking, or application architectures:

One of the worst things that can happen to anyone selecting equipment for a new network infrastructure is to receive the End-of-Life notice a week after the gear has been deployed in a production network… or maybe it’s even worse to be stuck with a neglected piece of technology full of bugs that the vendor never fixes because they’re chasing other shinier squirrels.

If you’re careful and watch what the vendors are doing, you might be able to save the day and identify the early phases of product decline. Here they are (as seen from the outside) in approximate order:

End of promotion opportunities. In most corporations aggressive hunters fare better than meticulous farmers, and product development is no different. As a friend of mine working for a large corporation once said “The culture here rewards launches instead of steady improvements. Like in academia, publishing a paper is valued more than running ISS”.

Remember the Windows version that was so security-focused that it broke everything, and needed a gazillion changes/updates/upgrades to get back to where you had a working computer? I think it was Vista, but maybe my memory is failing me. Anyway, Apple got its Vista moment with macOS Catalina.

I was stupid enough to upgrade just before New Year, and I’m still struggling with aftereffects and skeletons falling out of every cupboard I look at. I appreciate Apple trying to make their operating system ever more secure, but breaking stuff every time I upgrade it is borderline ridiculous.

The next time the sales system engineer working for your beloved $vendor drops by with a glitzy unicorn-based slide deck full of AI/ML goodies, read this article to get a slightly better understanding of where we are... from the perspective of someone who has actual experience doing that stuff.

What better way to start How Networks Really Work webinar than with fallacies of distributed computing… and that’s exactly what I did in late August 2019.

I always tell networking engineers attending our Building Network Automation Solutions online course to create minimalistic data models with (preferably) no redundant information. Not surprisingly, that’s a really hard task (see this article for an example) - using a simple automation tool like Ansible you end with either a messy and redundant data model or Jinja2 templates (or Ansible playbooks) full of hard-to-understand and impossible-to-maintain business logic.

Stephen Harding solved this problem the right way: his data center fabric deployment solution uses a dynamic inventory script that translates operator-friendly fabric description (data model) into template-friendly set of device variables.

Another EVPN reader question, this time focusing on auto-RD functionality and how it works with duplicate MAC addresses:

If set to Auto, the RD generated for the same VNI across the EVPN switches will be different. If the same route (MAC/IP) is present under different leaves of the same L2VNI, there is no best path selection (since the RD is different), and both will be considered. This is a misconfiguration and shouldn’t be allowed. How will the BGP deal with this?

If you’re running a typical (somewhat outdated) enterprise data center, you’re using tons of VLANs and firewalls, use VLANs as security zones, and push inter-VLAN traffic through firewalls for inspection. Security vendors love that approach - when inspecting traffic they can add no value to (like database- or backup sessions), the firewalls quickly become choke points that have to be upgraded.

Here’s an interesting tidbit from “Last Week in AWS” blog:

From a philosophical point of view, AWS fundamentally considers an API to be a promise. Services that aren’t promoted anymore are still available […] Think about that for a second - a service launched 13 years ago is still actively supported to the point where you can use it today.

Compare that to Killed By Google graveyard, and you might understand why I’m a bit reluctant to cover GCP in my webinars.

Stumbled upon a 35-year-old article describing the ironies of automation (HT: The Morning Paper). Here’s a teaser…

Unfortunately automatic control can ‘camouflage’ system failure by controlling against the variable changes, so that trends do not become apparent until they are beyond control.

In simpler words: when things fail, they fail really badly because the intermittent failures were kept hidden. Keep that in mind the next time someone tells you how wonderful software-defined AI-assisted networking is going to be.

Found a nice article about Margaret Hamilton, the lady who coined the term "software engineering".

Engineering—back in 1969 as well as here in 2020—carries a whole set of associated values with it, and one of the most important is the necessity of proofing for disaster before human usage. You don’t “fail fast” when building a bridge: You ensure the bridge works first.

Now be a good "networking engineer" and go and stretch another VLAN around the globe... ;)

The last Software Gone Wild podcast recorded in 2019 focused on advances in Linux networking - in particular on interesting stuff presented at NetDev 0x13 conference in Prague. The guests (in alphabetical first name order) Jamal Hadi Salim, Shrijeet Mukherjee, Sowmini Varadhan, and Tom Herbert shared their favorite topics, and commented on the future of Linux networking.

It's amazing how heaping layers of complexity (see also: SDN or intent-based whatever) manages to destroy performance faster than Moore's law delivers it. The computer with lowest keyboard-to-screen latency was (supposedly) Apple II built in 1983, with modern Linux having keyboard-to-screen RTT matching the transatlantic links.

No surprise there: Linux has been getting slower with every kernel release and it takes an enormous effort to fine-tune it (assuming you know what to tune). Keep that in mind the next time someone with a hefty PPT slide deck will tell you to build a "provider cloud" with packet forwarding done on Linux VMs. You can make that work, and smart people made that work, but you might not have the resources to replicate their feat.

I should have known better, but I couldn’t resist being pulled into a Twitter spat around the question “whether networking engineers need to know something about math” a long while ago.

Before going into the details, let’s start with Wikipedia definition: “Engineering is the use of scientific principles to design and build machines, structures, and other things” including “specific emphasis on particular areas of applied mathematics, applied science, and types of application”.

So feel free to believe that you don’t need any math or other science (because there’s very little science behind what we do in networking) in your job, in which case you might want to stop reading… but then at least please think twice about your job title.