One of my subscribers sent me an interesting puzzle:

One of my colleagues configured a single-area OSPF process in a customer VRF customer, but instead of using area 0, he used area 123 nssa. Obviously it works, but I was thinking: “What the heck, a single OSPF area MUST be in Area 0”

Not really. OSPF behaves identically within an area (modulo stub/NSSA behavior) regardless of the area number. Even there, you could argue that the only difference between area 0 and other areas is that the standard (and all compliant implementations) doesn’t allow you to set stub or NSSA bit in area 0.

In my quest to understand how much buffer space we really need in high-speed switches I encountered an interesting phenomenon: we no longer have the gut feeling of what makes sense, sometimes going as far as assuming that 16 MB (or 32MB) of buffer space per 10GE/25GE data center ToR switch is another $vendor shenanigan focused on cutting cost. Time for another set of Fermi estimates.

Let’s take a recent data center switch using Trident II+ chipset and having 16 MB of buffer space (source: awesome packet buffers page by Jim Warner). Most of switches using this chipset have 48 10GE ports and 4-6 uplinks (40GE or 100GE).

We got pretty far in our data deduplication in network data model journey, from initial attempts to network modeled as a graph… but we still haven’t got rid of all the duplicate information.

For example, if we have multiple devices connected to the same subnet, why should we have to specify IP address and subnet mask for every device (literally begging the operators to make input errors). Wouldn’t it be better (assuming we don’t care about exact IP addresses on core links) to assign IP addresses automatically?

The No Scripting Required to Start Your Automation Journey blog post generated lively discussions (and a bit of trolling from the anonymous peanut gallery). One of the threads focused on “how does automation work in real life IT department where it might be challenging to simplify operations before automating them due to many exceptions, legacy support…”

Here’s a great answer provided by another reader:

Roy Chua (SDx Central) published a blog post titled “Where Have All the SDN Controllers Gone” a while ago describing the gradual disappearance of SDN controller hype.

No surprise there - some of us were pointing out the gap between marketing and reality years ago.

It was evident to anyone familiar with how networking actually works that in a generic environment the drawbacks of orthodox centralized control plane SDN approach far outweigh its benefits. There are special use cases like intelligent patch panels where a centralized control plane makes sense.

This blog post was initially sent to subscribers of my SDN and Network Automation mailing list. Subscribe here.

At the end of my vNIC 2018 keynote speech I made a statement along these lines:

The moment you start using GUI with an SDN product you’re back to square one.

That claim confused a few people – Mark left this comment on my blog:

Approximately two years ago I tried to figure out whether aggressive marketing of deep buffer data center switches makes sense, recorded a few podcasts on the topic and organized a webinar with JR Rivers.

Not surprisingly, the question keeps popping up, so it seems it’s time for another series of TL&DR articles. Let’s start with the basics:

Remember the avoid duplicate data in network automation data models challenge and the restructuring we did to represent a network as a graph.

Well, I was not happy with the end result - I hated the complexity of supporting Jinja2 templates that had to check left- and right nodes of a link, so I generalized the data structure a bit, and all of a sudden I could model stub interfaces, P2P links and multi-access networks.

A while ago, I had an interesting consulting engagement: a multinational organization wanted to migrate off global Carrier Ethernet VPN (with routers at the edges) to MPLS/VPN.

While that sounds like the right thing to do (after all, L3 must be better than L2, right?), in that particular case, they wanted to combine the provider VPN with an Internet-based IPsec VPN. Doing that in parallel with MPLS/VPN tends to become an interesting exercise in “how convoluted can I make my design before I give up and migrate to BGP.”

Found a fantastic list of common logical fallacies. It's a must read for anyone having at least occasional interaction with non-Vulcans... and when you stop laughing (or screaming, or both) make sure you go through the companion web site to understand bugs in your wetware that sabotage your attempts at being perfectly logical.