SwiNOG 41: It Was Nice to Be Back

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:

Generate Partial Device Configurations with netlab

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.

On Generating EVPN MAC/IP Routes

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:

Worth Reading: Lab as Code (containerlab and netlab)

@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:

State of Network Automation with Urs Baumann

I stopped tracking the (lack of) progress in network automation years ago, when I realized I had nothing new to say. As an eternal optimist, I hoped I was just missing something, but Urs Baumann (the guest of Software Gone Wild Episode 206) destroyed my hopes when he said, “I can still use the same slides I created 10 years ago”. On a more positive note, he recently completed his Master’s thesis on AI in network engineering, so we ended with a nice chat on its potential impact.

Worth Reading: AI and Knowledge Stagnation

Another week, another interesting AI article (is anyone writing about anything else these days?), this time from Noah Smith (another author worth following). I found this gem hidden in his weekly roundup:

Instead of trying to write a piece of code from scratch, or prove a math theorem from scratch, or figure out some piece of knowledge for yourself, you just ask AI to do it all for you. So everyone ends up getting the right answers to questions whose answers are already known, so they don’t end up adding anything new.

Read more …

Ten Years of ITNOG

I spent the last two days in Bologna at ITNOG 10 in the excellent company of Italian networking engineers (many of them personal friends) and a few guests from around the world. As always, the organizers and the program committee didn’t disappoint – it was a smoothly organized, lovely event full of interesting presentations. Thanks a million to everyone involved; I’ll definitely be back!

Now for the highlights, starting with the ultimate catnip for the differently attentive: running two presentations in parallel on the same screen with the soundtrack distributed via headphones. I’ve never seen anything like that, and while it looked weird (I have no idea how the presenters took it), it turned out to be very useful, as you could easily tune out AI-washing presentations and switch to something more interesting. On the other hand, you could be faced with a hard choice of having to select one of two excellent presentations:

Hmmm: Rail-Optimized Networking for AI Workloads

Phil Gervasi wrote an interesting article describing Rail-Optimized Networking for AI Training Workloads. Go read it first; I’ll wait.

Does it sound interesting? Were you able to see behind the curtain and figure out what it’s really about?

SR-MPLS Workshop Materials

We had a wonderful SR-MPLS workshop @ ITNOG 10 in Bologna on April 20th 2025. If you missed it, explore:

• The Segment Routing: from Theory to Practice presentation by Tiziano Tofoni
• The slide deck for the hands-on part of the workshop
• The lab topologies, and the usage guidelines.

Lab: Integrated Routing and Bridging (IRB) with EVPN MAC-VRF Instances

Most EVPN documentation rushes into the complexities of symmetric IRB, type-5 EVPN routes, and EVPN IP-VRFs, but if you want to master a technology, it’s better to take it slow and proceed with small steps. In today’s lab exercise, we’ll do just that: explore what happens when you add IP addresses (we’ll use anycast gateways) to VLAN interfaces tied to EVPN MAC-VRF instances.

Testing FRRouting Pull Requests with netlab

Every other blue moon, I discover a bug in FRRouting (example). Because the FRRouting developers care about their work, it usually gets fixed within a few days, often resulting in a “can you test this PR?” question.

It turns out that’s surprisingly easy to do with netlab – here’s the step-by-step procedure (assuming you already have the topology file that reproduced the bug):

BGP Labs: Graceful Degradation for Unsupported Devices

A few weeks ago, I described the changes in the online BGP labs that allow you to use most of the common network operating systems as “external” routers¹. However, while we keep improving it, netlab still can’t configure all BGP features on all supported devices (PRs from Nokia and Mikrotik fans would be highly appreciated 😎), which means that it’s possible to configure your environment in a way where some of the more complex labs would simply fail to start.

The limited choice of devices for external routers was always well-documented (example), but if you insisted on using unsupported devices, the lab would fail to start with an error message, and you’d have to tweak the lab topology (example). Wouldn’t it be better to start the lab with a warning?

What is Netlab and Why Network Engineers Should Care

Milan Zapletal, the author of the biggest netlab topology I’ve seen so far (full story), has published a nice introductory article explaining What is Netlab and Why Network Engineers Should Care.

Thank you, Milan! Much appreciated ;)

netlab 26.04: EXOS, BGP Prefix Origination, More Static Routes

netlab release 26.04 is out. Here are the highlights:

• Extreme Networks EXOS is supported as a Vagrant box or containerlab node with OSPF, VLAN, and VRRP configuration (by Seb d’Argoeuves).
• The new bgp.advertise node attribute allows you to advertise networks in the IP routing table into BGP. It’s supported on most platforms.
• The bgp.originate attribute is now dual-stack and VRF-aware, allowing you to originate IPv4 and IPv6 prefixes into per-VRF BGP instances.
• New platforms with static route support: FortiOS (by Aleksey Popov), Nexus OS, Nokia SR OS, Nokia SR Linux. OpenBSD got discard static routes.

Public Videos: Docker 101

While according to the GIFEE True Believers™, Docker is dead and Kubernetes rules the world, people who want to have a bit of life might be perfectly happy running “obsolete” stuff like Docker on their laptops or Linux VMs.

If you happen to be one of the latter, you might like the Introduction to Docker webinar I put together a few years ago. It’s now public; you can watch it with an ipSpace.net account.

Looking for more binge-watching materials? You’ll find them here.

Interoperability of EVPN/VXLAN with IPv6 Next Hops

FRRouting release 10.6 promised “BGP IPv6 VTEP support,” claiming “it enables EVPN deployments using IPv6 tunnel endpoints while maintaining full backward compatibility with IPv4 VTEPs.” Of course, I had to try it out, and since we already have EVPN over IPv6 running on Arista EOS (since netlab release 26.01), I decided to set up a simple lab with an Arista cEOS device running release 4.35.2F and the latest FRRouting container.

I was not exactly surprised when it did not work. While Arista accepted FRRouting EVPN routes, the FRRouting BGP daemon rejected routes sent by Arista EOS:

Worth Reading: Shameless Guesses, Not Hallucinations

In a recent article, Scott Alexander made an interesting point: What AI produces are not hallucinations but shameless guesses (also known as bullshit) because the training process rewards the correct answers but does not penalize the incorrect ones. After all, having an AI model say, “I don’t know that” is not good for business, is it?

On a tangential note, calling those blunders hallucinations was a marketing masterstroke. Not being a native English speaker, I might be missing some nuances, but I feel like hallucinations might be something you’re not responsible for (some of the time), whereas we all know who’s responsible for bullshit and shameless guesses – and responsibility is something the AI companies are clearly trying to stay as far away from as possible.

On another tangential note, if you’re not following Scott Alexander’s blog substack, you’re missing out.