Dmytro Shypovalov published another article well worth reading: why should you use an SDN controller for RSVP-TE. It covers:

• The reasons people might still prefer RSVP-TE over SR-MPLS and the current state of RSVP-TE
• What an SDN controller might bring to the RSVP-TE world
• SR/RSVP coexistence and interworking

Have fun!

Last Monday, I decided to review and merge the “VXLAN on Cumulus Linux 5.x with NVUE” pull request. I usually run integration tests on the modified code to catch any remaining gremlins, but this time, all the integration tests started failing during the VM creation phase. I was completely weirded out, considering everything worked a week ago.

Fortunately, Vagrant debugging is pretty good¹ and I was quickly able to pinpoint the issue (full printout):

Donatas Abraitis asked me to spread the word about the first ever Baltic NOG meeting in the second half of September 2025 (more details)

If you were looking for a nice excuse to visit that part of Europe (it’s been on my wish list for a very long time), this might be a perfect opportunity to do it 😎.

On a tangential topic of fascinating destinations 😉, there’s also ITNOG in Bologna (May 19th-20th, 2025), Autocon in Prague (May 26th-30th, 2025), and SWINOG in Bern (late June 2025).

The results of netlab integration tests are stored in YAML files, making it easy to track changes improvements with Git. However, once I added the time of test and netlab version to the test results, I could no longer use git diff to figure out which test results changed after a test run – everything changed.

For example, these are partial test results from the OSPFv2 tests:

Whenever you’re faced with an “unexpected” network outage that doesn’t seem to be caused by a hardware failure, the root cause often tends to be a change in a device configuration, raising these questions:

• What changes were made to the device configuration?
• When were the changes made?
• Who made them?

Vini Motta decided to use AI on ipSpace.net content to find what it would recommend as the projects to work on in order to become employable in 2025. Here are the results he sent me; my comments are inline on a gray background.

Network Automation with Python

Project: Automate basic network tasks like device configuration, backup, or monitoring using Python scripts.

In the previous blog post, I described the usual mechanisms used to connect virtual machines or containers in a virtual lab, and the drawbacks of using Linux bridges to connect virtual network devices.

In this blog post, we’ll see how KVM/QEMU/libvirt/Vagrant use UDP tunnels to connect virtual machines, and how containerlab creates point-to-point vEth links between Linux containers.

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?