ipSpace.net blog

I don’t know why I decided to allow underscores in netlab node names.

Like OSPF, IS-IS was designed when router memory was measured in megabytes and clock speeds in megahertz.

The first IPv6 specs were published in 1995, and yet 30 years later, we still have a pretty active IETF working group focused on “developing guidelines for the deployment and operation of new and existing IPv6 networks.”

In 2007, Jeff Atwood published a legendary blog post summarizing a 1997 paper by Brian Foote and Joseph Yoder.

netlab release 25.12 (25.12.02 to be exact – I had a few PEBCAK moments) was published last Friday.

In the first VXLAN lab, we covered the very basics.

Sean Goedecke published an excellent set of recommendations for good technical writing, including: Keep it short Try to make your point in the first sentence Details matter less than you think.

What could be better than watching 0x02 Jeffs discuss networking?

Last week, we fixed the mismatched route targets in our sample multi-pod EVPN fabric.

Dan Partelly, a heavy netlab user (and an active contributor), sent me this interesting perspective on how one might want to use netlab without ever building a lab with it.

In his latest blog post (Systems design 3: LLMs and the semantic revolution), Avery Pennarun claims that LLMs might solve the problem we consistently failed to solve on a large scale for the last 60 (or so) years – the automated B2B data exchange.

Route redistribution into IS-IS seems even easier than its OSPFv2/OSPFv3 counterparts.

When I published a blog post making fun of the ridiculously incorrect Cisco IOS/XE OSPFv3 documentation, an engineer working for Cisco quickly sent me an email saying, “Well, the other vendors are not much better.”

Aleksandr Albin built a large (almost 20-router) lab topology (based on an example from Jeff Doyle’s Routing TCP/IP Volume 2) that he uses to practice inter-AS IP multicast.

Last week, we fixed the incorrect BGP next hops in our sample multi-pod EVPN fabric.

One would hope that the developers of a network operating system wouldn’t feel the irresistible urge to reinvent what should have been a common configuration feature for every routing protocol.

Dmitry Klepcha published an excellent document describing how you can use netlab to build a series of data center fabric labs, starting from a simple IP network (without routing) and finishing with a complex EVPN/VXLAN network using symmetric IRB and MLAG…

Vadim Semenov created a nice demo that allows you to use an LLM to query the collected link-state graphs through an MCP agent (SuzieQ would probably be faster and easier to deploy, but hey, AI).

Last month, I wrote about the specifics of troubleshooting multi-pod EVPN designs.

Remember the vendor consultants who persuasively told you how to use their gear to build a disaster recovery solution with stretched VLANs, even though the only disaster recovery they ever experienced was the frantic attempt to restart their PowerPoint sl…

In March 2024, I received my first PR from an airplane: Sander Steffann was flying to South Africa to deliver an Ansible training and fixed a minor annoyance in the then-new multilab feature.

I managed to push out netlab release 25.11 yesterday.

Many engineers who tried out (or use) various AI products would agree that they’re useful when used correctly, but way overhyped.

In September 2024, I described how you can build One-Arm Hub-and-Spoke VPN with MPLS/VPN.

Imagine you have an IPv4-only network1 and want to try out how to deploy a routing protocol for IPv6. netlab is a pretty good tool for the job as it: Creates an addressing scheme for you Designs a routing protocol deployment (OSPF, IS-IS) based on just a…

Like any other routing protocol, IS-IS has several timers you can tweak to improve the convergence speed of your network, or make your network unstable (eventually breaking it completely) if you reduce them too much (if you care about fast convergence, you

Someone asked for my DEEP 2025 presentation (Testing Disaster Recovery Designs).

Jason Gintert published an excellent explanation why AI won’t replace (all) network engineers, and reading it, I felt like reading one of my “automation won’t replace network engineers” blog posts.

We run two types of integration tests before shipping a netlab release: device integration tests that check whether we correctly implemented netlab features on all supported devices, and platform integration tests that check whether rarely-used core funct…

My first encounter with Ansible release 12 wasn’t exactly encouraging.

After launching the BGP labs in 2023 and IS-IS labs in 2024, it was time to start another project that was quietly sitting on the back burner for ages: open-source (and free) VXLAN/EVPN labs.

Pat Allen wrote an interesting guide for managers of networking teams dealing with the onslaught of AI (HT: PacketPushers newsletter).

Found this incredible gem1 hidden in the Usage Guidelines for the OSPFv3 router-id configuration command part of the Cisco IOS IPv6 reference guide.

netlab does not support a Syslog server (yet), but it’s really easy to add one to your lab topology, primarily thanks to the Rsyslog team publishing a ready-to-run container.

I love well-organized small conferences, so it wasn’t hard to persuade me to have another talk at the DEEP Conference in Zadar, Croatia.

Here’s a cool feature every routing protocol should have: a flag that tells everyone a node is going down, giving them time to adjust their routing tables before disrupting traffic flow.

Daniel Dib wrote a nice article describing the history of the loopback interface1, triggering an inevitable mention of the role of a loopback interface in OSPF and related flood of ancient memories on my end.

Today, I’ll focus on another feature of the new files plugin – you can use it to embed any (hopefully small) file in a lab topology (configlets are just a special case in which the plugin creates the relative file path from the configlets dictionary data).

Sometimes you want to assign IPv4/IPv6 subnets to transit links in your network (for example, to identify interfaces in traceroute outputs), but don’t need to have those subnets in the IP routing tables throughout the whole network.

In the multi-pod EVPN design, I described a simple way to merge two EVPN fabrics into a single end-to-end fabric.

Daniel Dib asked a sad question on LinkedIn: Where did all the great documentation go?

A few days ago, I described how you can use the new config.inline functionality to apply additional configuration commands to individual devices in a netlab-powered lab.

netlab release 25.10 includes: Support for container version of Cisco 8000v emulator (finally a reasonable IOS-XR platform) Support for vJunosEVO (vPTX) release 24+ (it needs UEFI BIOS), thanks to Aleksey Popov and Stefano Sasso Wildcards or regular expre…

An engineer reading my multi-pod EVPN article asked an interesting question: How do you handle troubleshooting when VTEPs cannot reach each other across pods?

TL&DR: You shouldn’t see any immediate impact of this change, but I’ll eventually clean up old stuff, so you might want to check the URLs if you use RSS/Atom feeds to get the list of ipSpace.net blog posts or podcast episodes.

When I first met David Gee, he worked for a large system integrator.

Here’s an interesting data point in case you ever wondered why things are getting slower, even though the CPU performance is supposedly increasing.

In this challenge lab, you’ll configure a BIRD daemon running in a container as a BGP route reflector in a transit autonomous system.

For years, netlab has had custom configuration templates that can be used to deploy custom configurations onto lab devices.

In the EVPN Designs: Layer-3 Inter-AS Option A, I described the simplest multi-site design in which the WAN edge routers exchange IP routes in individual VRFs, resulting in two isolated layer-2 fabrics connected with a layer-3 link.