I made a flippant remark in a blog comment…

While it’s academically stimulating to think about forwarding small packets (and applicable to large-scale VoIP networks), most environments don’t have to deal with those. Looks like it’s such a non-issue that I couldn’t find recent data; in the good old days ~50% of the packets were 1500 byte long.

… and Minh Ha (by now a regular contributor to my blog) quickly set me straight with a lengthy comment that’s too good to be hidden somewhere at the bottom of a page. Here it is (slightly edited). Also, you might want to read other comments to the original blog post for context.

Every now and then I get a question along the lines of “why can’t we have a distributed SDN controller (because resiliency) that would survive network partitioning?” This time, it’s not the incompetency of solution architects or programmers, but the fundamental limitations of what can be done when you want to have consistent state across a distributed system.

TL&DR: If your first thought was CAP Theorem you’re absolutely right. You can probably stop reading right now. If you have no idea what I’m talking about, maybe it’s time you get fluent in distributed systems concepts after you’re finished with this blog post and all the reference material linked in it. Don’t know where to start? I put together a list of resources I found useful.

Long long time ago in a country far far away when traveling was still a thing I led an interesting data center fabric design workshop. We covered tons of interesting topics, including automating network services deployments (starting with VLAN self-service for server admins).

As was often the case in my workshops, we had representatives from multiple IT teams sitting in the room, and when I started explaining how I’d automate VLAN deployments, the server administrator participating in the workshop quickly chimed in: “that’s exactly how I implemented self-service for some of our customers, it makes perfect sense to use the same approach for server port and VLAN provisioning”, and everyone else in the room agreed… apart from the networking engineer, who used a counter-argument along the lines of “we only provision a new VLAN or server port every few days, we can do it by hand” and no amount of persuasion would move him.

One of the subscribers watching the Graph Algorithms in Networks webinar found the webinar had an interesting impact on his perspective (according to his feedback):

This is genuine content that I haven’t seen anywhere else. It helps to get up to speed on computer science topics that are relevant to network professionals. After attending this webinar, I couldn’t unsee the graphs anymore that are almost everywhere in networking.

This webinar is now free, as are other webinars by Rachel Traylor, including Network Connectivity, Graph Theory, and Reliable Network Design and Queuing Theory.

When I’d first seen BGP-LS I immediately thought: “it would be cool to use this to fetch link state topology data from the network and build a graph out of it”. In those days the only open-source way I could find to do it involved Open DayLight controller’s BGP-LS-to-REST-API converter, and that felt like deploying an aircraft carrier to fly a kite.

Things have improved dramatically since then. In Visualizing BGP-LS Tables, HB described how he solved the challenge with GoBGP, gRPC interface to GoBGP, and some Python code to parse the data and draw the topology graph with NetworkX. Enjoy!

Something to keep in mind before you start complaining about the crappy state of network operating systems: people are still finding hundreds of bugs in C and C++ compilers.

One might argue that compilers are even more mission-critical than network devices, they’ve been around for quite a while, and there might be more people using compilers than configuring network devices, so one would expect compilers to be relatively bug-free. Still, optimizing compilers became ridiculously complex in the past decades trying to squeeze the most out of the ever-more-complex CPU hardware, and we’re paying the price.

Keep that in mind the next time a vendor dances by with a glitzy slide deck promising software-defined nirvana.

Regardless of the technology used to get packets across the network, someone has to know how to get from sender to receiver(s), and as always, you have multiple options:

• Almighty controller
• On-demand dynamic path discovery (example: probing)
• Participation in a routing protocol

For more details, watch Finding Paths Across the Network video.

More than a year ago I was enjoying a cool beer with my friend Nicola Modena who started explaining how he solved the “you don’t need IP address renumbering for disaster recovery” conundrum with production and standby VRFs. All it takes to flip the two is a few changes in import/export route targets.

I asked Nicola to write about his design, but he’s too busy doing useful stuff. Fortunately he’s not the only one using common sense approach to disaster recovery designs (as opposed to flat earth vendor marketectures). Adrian Giacometti used a very similar design with one of his customers and documented it in a blog post.

A long-time reader sent me a series of questions about the impact of WAN partitioning in case of an SDN-based network spanning multiple locations after watching the Architectures part of Data Center Fabrics webinar. He therefore focused on the specific case of centralized control plane (read: an equivalent of a stackable switch) with distributed controller cluster (read: switch stack spread across multiple locations).

Minh Ha left the following rant as a comment on my 5-year-old What Are The Problems with Broadcom Tomahawk? blog post. It’s too good to be left gathering dust there. Counterarguments and other perspectives are highly welcome.

So basically a lot of vendors these days are just glorified Broadcom resellers :p. It’s funny how some of them try to up themselves by saying they differentiate their offerings with their Network OS.

Almost exactly a year ago Miha Markočič joined the ipSpace.net team. He was fresh out of university, fluent in Python, but with no networking or automation background… so I decided to try my traditional method of getting new team members up to speed: throw them into the deep water, observe how quickly they learn to swim, and give them a few tips if it seems like they might be drowning.

It worked out amazingly well. Miha quickly mastered the intricacies of AWS and Azure, and created full-stack automation solutions in Ansible, Terraform, CloudFormation and Azure Resource Manager to support the AWS and Azure webinars, and the public cloud networking online course.

Arista published a blog post describing the details of forwarding table sizes on 7050QX-series switches. The description includes the base mode (fixed tables), unified forwarding tables and even the IPv6 LPM details, and dives deep into what happens when the switch runs out of forwarding table entries.

Too bad they’re describing an ancient Trident-2 ASIC (I last mentioned switches using it in 2017 Data Center Fabrics update). Did NDA expire on that one?

Decades ago I understood the intricacies of AAA on Cisco IOS. These days I wing it and keep throwing spaghetti at the virtual wall until something sticks and I can log in (after all, it’s all in a lab, and I’m interested in routing protocols not interactions with TACACS+ server).

If you’re experiencing similar challenges you might appreciate AAA Deep Dive on Cisco Devices by the one and only Daniel Dib.

This podcast introduction was written by Nick Buraglio, the host of today’s podcast.

In today’s evolving landscape of whitebox, brightbox, and software routing, a small but incredibly comprehensive routing platform called FreeRTR has quietly been evolving out of a research and education service provider network in Hungary. 

Kevin Myers of IPArchitechs brought this to my attention around March of 2019, at which point I went straight to work with it to see how far it could be pushed.

When I blogged about release 0.2 of my lab-building tool, Kristian Larsson was quick to reply: “now do vrnetlab”. You could guess what my reply was (hint: “submit a pull request”), but I did realize I’d have to add multi-provider support before that would make sense.

Release 0.3 adds support for multiple virtualization providers. You can run six different platforms on vagrant-libvirt (assuming you build the boxes), and I added rudimentary support for Vagrant provider for VirtualBox: