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Blog Posts in August 2020

Review Questions: Switching, Bridging and Routing

One of the most annoying part in every training content development project was the ubiquitous question somewhere at the end of the process: “and now we’d need a few review questions”. I’m positive anyone ever involved in a similar project can feel the pain that question causes…

Writing good review questions requires a particularly devious state of mind, sometimes combined with “I would really like to get the answer to this one” (obviously you’d mark such questions as “needs further research”, and if you’re Donald Knuth the question would be “prove that P != NP").

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Docker Swarm Services behind the Scenes

Remember the claim that networking is becoming obsolete and that everyone else will simply bypass the networking teams (source)?

Good news for you – there are many fast growing overlay solutions that are adopted by apps and security teams and bypass the networking teams altogether.

That sounds awesome in a VC pitch deck. Let’s see how well that concept works out in reality using Docker Swarm as an example (Kubernetes is probably even worse).

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MUST READ: What I've learned about scaling OSPF in Datacenters

Justin Pietsch published a fantastic recap of his experience running OSPF in AWS infrastructure. You MUST read what he wrote, here’s the TL&DR summary:

  • Contrary to popular myths, OSPF works well on very large leaf-and-spine networks.
  • OSPF nuances are really hard to grasp intuitively, and the only way to know what will happen is to run tests with the same codebase you plan to use in production environment.

Dinesh Dutt made similar claims on one of our podcasts, and I wrote numerous blog posts on the same topic. Not that anyone would care or listen, it’s so much better to watch vendor slide decks full of latest unicorn dust… but in the end, it’s usually not the protocol that’s broken, but the network design.

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Worth Reading: Seamless Suffering

When someone sent me a presentation on seamless MPLS a long while ago my head (almost) exploded just by looking at the diagrams… or in the immortal words of @amyengineer:

“If it requires a very solid CCIE on an obscure protocol mix at 4am, it is a bad design” - Peter Welcher, genius crafter of networks, granter of sage advice.

Turns out I was not that far off… Dmytro Shypovalov documented the underlying complexity and a few things that can go wrong in Seamless Suffering.

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MUST READ: IPv4, IPv6, and a Sudden Change in Attitude

Avery Pennarun continued his if only IPv6 would be less academic saga with a must-read IPv4, IPv6, and a sudden change in attitude article in which he (among other things) correctly identified IPv6 as a typical example of second-system effect:

If we were feeling snarky, we could perhaps describe IPv6 as “the String Theory of networking”: a decades-long boondoggle that attracts True Believers, gets you flamed intensely if you question the doctrine, and which is notable mainly for how much progress it has held back.

In the end, his conclusion matches what I said a decade ago: if only the designers of the original Internet wouldn’t be too stubborn to admit a networking stack needs a session layer. For more details, watch The Importance of Network Layers part of Networks Really Work webinar

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Must Watch: How NOT to Measure Latency

A while ago someone pointed me to an interesting talk explaining why 99th percentile represents a pretty good approximation of user-experienced latency on a typical web page (way longer version: Understanding Latency and Application Responsiveness, also How I Learned to Stop Worrying and Love Misery)

If you prefer reading instead of watching videos, there’s also everything you know about latency is wrong.

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