A lot of AI-coding enthusiasts are making claims along the lines of “AI coding tools are like compilers; you supply intent, they translate it into code, and who ever looked at the machine-code output?” Unfortunately, there is a bit of a gap between hope and reality; traditional compilers were always deterministic, and are (after decades of development and bug-fixing) pretty much bug-free. AI coding tools are neither, and no amount of “agentic loops” will solve that.

Sakar left an interesting comment on my The Curious Case of the BGP Connect State blog post, claiming that Cisco IOS/XE goes through a CONNECT state when opening an incoming BGP session.

I wanted to double-check this behavior, so I needed a scenario where one router would keep sending TCP SYN requests, the other would not (or we wouldn’t learn anything), and the two routers could not communicate (or they’d quickly go into the OPEN state).

Here’s my first attempt at meeting those requirements:

Remember the sage advice to simplify your life and use the IPv6 /64 prefixes everywhere? Not only does it make your life simpler (and wastes immesuarably less address space than the crazy “let’s assign /64 to every device” stupidity), it also reduces the hardware requirements in your high-speed routers layer-3 switches. You see, doing lookups on 64 bits uses half the silicon it takes to do lookups on 128 bits.

Alas, some people never got the memo. OSPFv3 standard clearly states in one of the bullets in section 4.4.3.9 that the loopback prefixes should always be advertised as /128s regardless of what’s configured on the interface.

Tony Mattke put together a long list of recommendations that might help you get more out of your LLM tokens.

Definitely worth reading instead of yelling at the stupid AI.

netlab is using the Python Box library to make the code easier to read¹. When I started the project, I hated the way you fetch values from Python dictionaries with stuff like node['ospf']['area']; Python Box lets you write node.ospf.area. Even better², you can tell Python Box to create intermediate dictionaries as needed. node.ospf.area = 1 will automatically create the node.ospf dictionary.

But wait, there’s more (yes, we’re getting to the topic of today’s blog post): Box lets you use the same dotted notation in YAML files.

Last Friday, I had a lovely chat with Steinn Bjarnarson and Urs Baumann, resulting in the NetworkAutoMagic episode 11. We couldn’t avoid mentioning netlab, the seven layers of ACL hell (which is still balmy compared to the QoS hell), and the gotchas of AI-generated device configurations.

Fortunately, I don’t have to go into more details; Steinn published extensive notes, and if you don’t feel like listening to us while driving, you can waste time watching us on YouTube.

netlab release 26.08 brings a few humongous additions:

• ArcOS support by @roc-ops
• VPP (FD.io) with FRR or BIRD control plane by @jbemmel
• SONiC containers (also by @roc-ops)
• IPv4/IPv6 access control lists in the routing module by @DanPartelly

But wait, there’s more:

Remember the anonymous troll who chided me for writing a rant instead of opening a GitHub issue in the relevant Ansible repository? Well, I decided to be an open-source poster boy when I stumbled upon the next Ansible bug, and ended up feeling like a sweet summer child :(

Last December, I wrote a pretty ranty post explaining how Ansible release 12 broke (some?) network device configuration playbooks. The inevitable anonymous troll (why are they always anonymous?) couldn’t resist asking whether I opened an issue on GitHub. I didn’t (more about that later), but when the solution to that rant was “we’re deprecating using templates in src” parameter, I opened an issue arguing why that’s not a good idea.

Tony Mattke published a blog post I wish I’d read 10 years ago. His Oh-Shit Toolkit includes several tools one can use after messing up Git branches or commit history.

Definitely worth reading, even if you’ve been working with Git for ages.