Another year is almost gone, and it’s time for my traditional “I will disappear until mid-January” retreat (also, don’t expect me to read my email until I’m back).

I hope you’ll also be able to disconnect from the crazy pace of the networking world, forget the “AI will make networking engineers obsolete” shenanigans (hint: SDN did not), and focus on your loved ones. I would also like to wish you all the best in 2025!

Addy Osmani published an excellent overview of the challenges of AI-assisted coding. They apply equally well to the “AI will generate device configurations for me” or “AI will troubleshoot my network” ideas (ignoring for the moment the impact of the orders-of-magnitude smaller training set), so it’s definitely worth reading.

I particularly liked the “‌AI is like having a very eager junior developer on your team” take, as well as the description of the “70% problem” (AI will get you 70% there, but the last 30% will be frustrating) – a phenomenon perfectly illustrated by the following diagram by Forrest Brazeal:

As much as I love explaining how to use BGP in an optimal way, sometimes we have to do what we know is bad to get the job done. For example, if you have to deal with clueless ISPs who cannot figure out how to use BGP communities, you might be forced to use the Big Hammer of disaggregated prefixes. You can practice how that works in the next BGP lab exercise.

My Internet Routing Security talk from last year’s DEEP conference (a shorter version of the Internet Routing Security webinar) is now available on YouTube.

Hope you’ll find it useful ;)

We were always told that Open Shortest Path First (OSPF) is a fast converging link-state routing protocol that always results in a loop-free and blackhole-free network topology. In reality, it’s a link-state protocol within an area and almost a distance-vector protocol between areas.

In this article, I’ll illustrate how this unexpected behavior can affect the convergence of your network and how you can use proprietary extensions of Cisco IOS to alleviate the undesired side effects of OSPF.

A fellow networking engineer recently remarked, “FRRouting automatically selects the correct [IBGP] source interface even when not configured explicitly.”

TL&DR: No, it does not. You were just lucky.

Basics first¹. BGP runs over TCP sessions. One of the first things a router does when establishing a BGP session with a configured neighbor is to open a TCP session with the configured neighbor’s IP address.

On December 9th, 2020, I created a new GitHub repository and pushed the first commit of my “I hate creating Vagrantfiles by hand” tool. It could create Vagrantfile and Ansible inventory from a (very rudimentary) network topology and deploy handcrafted device configurations on Cisco IOS and Arista EOS.

When I discovered GitHub Codespaces (thanks to a pointer by Roman Dodin), I did the absolute minimum of research to get netlab up and running in a container to enable Codespaces-based labs (BGP, IS-IS) and netlab examples.

However, if you want to know the behind-the-scenes details, you MUST read the Codespaces for Network Engineers and Educators deep dive by Julio Perez.

This blog post discusses an old arcane question that has been nagging me from the bottom of my Inbox for almost exactly four years. Please skip it if it sounds like Latin to you, but if you happen to be one of those readers who know what I’m talking about, I’d appreciate your comments.

Terminology first:

• Prefix Independent Convergence allows entries in the forwarding table to point to shared next hops (or next-hop groups), reducing the FIB update bottleneck when changing the next hop for a large number of prefixes (for example, when dealing with a core link failure). More details in the initial blog post and PIC applicability to fast reroute.
• PIC Edge (as defined by vendor marketing) is the ability to switch to a backup CE route advertised to a backup PE router before the network convergence is complete.

Here’s (in a nutshell) how PIC Edge is supposed to work:

A happy netlab user asked for a sample Cisco ASAv topology that would include an inside and an outside router.

We don’t have anything similar in the netlab examples yet, so let’s build a simple topology with two routers, a firewall, and a few hosts.

However, we have to start with a few caveats: