I mostly gave up on LLMs being any help (apart from generating copious amounts of bullshit), but I still thought that generating summaries might be an interesting use case. I was wrong. As Gerben Wierda explains in his recent “When ChatGPT summarises, it actually does nothing of the kind” blog post, you have to understand a text if you want to generate a useful summary, and that’s not what LLMs do. They can generate a shorter version of the text, which might not focus on the significant bits ..read more

Using the typical default router configurations, it can take minutes between a failure of an inter-AS link and the convergence of BGP routes. You can fine-tune that behavior with BGP timers and BFD (and still get pwned by Graceful Restart). While you can’t influence link failures, you could drain the traffic from a link before starting maintenance operations on it, and it would be a shame not to do that considering there’s a standard way to do that – the GRACEFUL_SHUTDOWN BGP community defined in RFC 8326. That’s what you’ll practice in the next BGP lab exercise. Explore the lab exercise ..read more

Tom Limoncelli wrote another must-read masterpiece: sometimes you’ll save time if you make two trips instead of one. The same lesson applies to network design: cramming too many features into a single device will inevitably result in complex, hard-to-understand configurations and weird bugs. Sometimes, it’s cheaper to split the required functionality across multiple devices ..read more

The recent IBGP Full Mesh Between EVPN Leaf Switches blog post generated an interesting discussion on LinkedIn focused on whether we need route reflectors (in small fabrics) and whether they do more harm than good. Here are some of the highlights of that discussion, together with a running commentary. Please note that we’re talking about BGP route reflectors in reasonably small data center fabrics. Large service provider networks with millions of customer VPN routes are a completely different story. As always, what you read in a random blog post might not apply to your network design. YMMV. Re ..read more

Many network automation solutions generate device configurations from a data model and deploy those configurations. Last week, we focused on “how do we know the device data model is correct?” This time, we’ll take a step further and ask ourselves, “how do we know the device configurations work as expected?” There are four (increasingly complex) questions our tests should answer: Read more ..read more

AWS started charging for public IPv4 addresses a few months ago, supposedly to encourage users to move to IPv6. As it turns out, you need public IPv4 addresses (or a private link) to access many AWS services, clearly demonstrating that it’s just another way of fleecing the sheep Hotel California tax. I’m so glad I moved my videos to Cloudflare ;) For more details, read AWS: Egress Traffic and Using AWS Services via IPv6 (rendered in beautiful, easy-to-read teletype font ..read more

In the previous blog post in the EVPN Designs series, we explored the simplest possible VXLAN-based fabric design: static ingress replication without any L2VPN control plane. This time, we’ll add the simplest possible EVPN control plane: a full mesh of IBGP sessions between the leaf switches. This blog post describes an initial BGP design that we’ll refine in subsequent blog posts. Having a full mesh of IBGP sessions between leaf switches is a bad idea unless you have a tiny fabric or you’re deploying a small-scale EVPN pilot. Read more ..read more

Let’s open another juicy can of BGP worms: load balancing. In the first lab exercise, you’ll configure equal-cost load balancing across EBGP paths and tweak the “What is equal cost?” algorithm to consider just the AS path length, not the contents of the AS path. Explore the lab exercise ..read more

All the Kubernetes Service Mesh videos from the Kubernetes Networking Deep Dive webinar with Stuart Charlton are now public. Enjoy! Explore ..read more

Daniel Dib found the ancient OSPF Protocol Analysis (RFC 1245) that includes the Router CPU section. Please keep in mind the RFC was published in 1991 (35 years ago): Steve Deering presented results for the Dijkstra calculation in the “MOSPF meeting report” in [3]. Steve’s calculation was done on a DEC 5000 (10 mips processor), using the Stanford internet as a model. His graphs are based on numbers of networks, not number of routers. However, if we extrapolate that the ratio of routers to networks remains the same, the time to run Dijkstra for 200 routers in Steve’s implementation was around ..read more