It all started with a netlab issue describing different interpretations of VLAN 1 in a trunk. While Cumulus NVUE (the way the netlab configuration template configures it) assumes that the VLAN 1 in a trunk is tagged, Arista EOS assumes it’s the native VLAN.

At that point, I should have said, “that’s crazy, we shouldn’t allow that” and enforce the “VLAN 1 has to be used as a native VLAN” rule. Alas, 20/20 hindsight never helped anyone.

TL&DR: Do not use VLAN 1 in VLAN trunks; if you have to, use it as a native VLAN.

The initial IS-IS labs covered the IS-IS basics. It’s time to move on to interesting IS-IS features (and why you might want to use them), starting with passive IS-IS interfaces.

In the Concise Link Descriptions blog post, I described various data formats that you could use to concisely list nodes attached to a link. Today, we’ll focus on a mechanism that helps you spot errors in your topology: a dictionary of links.

Imagine you have a large topology with dozens of links, and you get an error saying, “there is this problem with links[17]”. It must be great fun counting the links to find which one triggered the error, right?

Once a virtual machine running a network operating system boots, you’d expect its data-plane interfaces to be operational, right? Some vendors disagree. It takes over a minute for some network operating systems to figure out they have this thing called interfaces.¹

I would love to figure out what takes them so long (a minute is an eternity on modern CPUs), but I guess we’ll never know.

Behind the Scenes

netlab uses two device provisioning mechanisms: it can start virtual machines with Vagrant or containers with containerlab. Some of those containers might use KVM/QEMU to run a hidden virtual machine (see also: RFC 1925 rule 6a).

A few days ago, someone mentioned Arista released a cEOS EFT image running on Arm. Of course, I had to test whether it would run on Apple Silicon.

TL&DR: YES 🎉 🎉

Here’s what you have to do to make the Arista cEOS container work with netlab running on an Ubuntu VM on Apple silicon:

There are three major ways to connect network devices in the physical world:

• Point-to-point links between devices (usually using some variant of Ethernet)
• Multi-access layer-1 networks running some IEEE 802.x encapsulation on top of that (GPON, WiFi, Ethernet hubs)
• Multi-access switched layer-2 network (dumb switches, hopefully running some STP variant)

Implementing these connections in virtual labs is a bit harder than one might think, as all virtualization solutions assume you plan to run virtual servers connected to Ethernet segments.

During the last three weeks, we were busy squashing bugs (device configuration fixes, other bug fixes). Some were recent; others were ancient pests uncovered by better integration tests. The end result: netlab release 1.9.4.

netlab release 1.9.4 passed hundreds of integration tests and should be a better choice than the previous 1.9 releases. To upgrade, execute pip3 install --upgrade networklab.

Update: 2025-02-03

We still missed a few quirks :( Release 1.9.4-post1 addresses those (and, unfortunately, I’m pretty sure there will be more).

I got this question from Paul:

Have you ever seen a BGP peer in the “Connect” state? In 20 years, I have never been able to see or reproduce this state, nor any mention in a debug/log. I am starting to believe that all the documentation is BS, and this does not exist.

The BGP Finite State Machine (FSM) (at least the one defined in RFC 4271 and amended in RFC 9687) is “a bit” hard to grasp but the basics haven’t changed from the ancient days of RFC 1771:

Dalton Ortega, Cisco Modeling Labs Product Manager, sent me the following email as a response to my Configuring IP Addresses Won't Make You an Expert blog post:

First, your statement on Autonetkit is indeed correct. We had removed that from the product due to lack of popularity. That being said, in our roadmap we are looking at methods to reintroduce on-the-fly configuration as well as enhancing our sample labs library to make getting started with CML easier.

Secondly, CML can be run in full IaC mode because of the API-first build. In fact, many of our customers are using CML as an automated test/validation bed for their CI/CD pipelines. Tools like Ansible and Terraform are available to facilitate this inside CML too. For more details, read:

• Get Started With Terraform and Cisco Modeling Labs
• How to Use Ansible with CML

George V. Neville-Neil published a fantastic, must-read summary of the various code copilots’ usefulness on ACM Queue: The Drunken Plagiarists.

It pretty much mirrors my experience (plus, I got annoyed when the semi-relevant suggestions kept kicking me out of the flow) and reminds me of the early days of OpenFlow, when nobody wanted to listen to old grunts like myself telling the world it was all hype and little substance.