Blog Posts in May 2025
Response: CLI Is an API
Andrew Yourtchenko and Dr. Tony Przygienda left wonderful comments to my Screen Scraping in 2025 blog post, but unfortunately they prefer commenting on a closed platform with ephemeral content; the only way to make their thoughts available to a wider audience is by reposting them. Andrew first:
I keep saying CLI is an API. However, it is much simpler and an easier way to adapt to the changes, if these three conditions are met:
netlab 2.0.0: Hosts, Bridges, and SRv6
netlab release 2.0.0 is out. I spent the whole week fixing bugs and running integration tests, so I’m too brain-dead to go into the details. These are the major features we added (more about them in a few days; the details are in the release notes):
- Well-defined node roles (host, router, bridge) are now available on multiple platforms
- The firewall.zonebased plugin allows you to configure a rudimentary firewall
- SRv6: BGP L3VPN support is now available for FRRouting, so you can go out and kick its (free) tires.
- bridge nodes can be used as simple bridges or to implement multi-access links
- netlab defaults command provides sysctl-like CLI interface to user/system defaults.
Other changes include:
Forwarding Packets Across a Network
After inspecting the confusing bridging/routing/switching terminology and a brief detour into the control/data plane details, let’s talk about how packets actually move across a network.
As always, things were simpler when networks were implemented with a single cable. In that setup, all nodes were directly reachable, and the only challenge was figuring out the destination node’s address; it didn’t matter whether it was a MAC address, an IP address, or a Fiber Channel address. On a single cable, you could just broadcast, like, “Who has this service?” and someone would reply, “I’m the printer you’re looking for.” That’s how many early non-IP protocols operated.
Screen Scraping in 2025
Dr. Tony Przygienda left a very valid (off-topic) comment to my Breaking APIs or Data Models Is a Cardinal Sin blog post:
If, on the other hand, the customers would not camp for literally tens of years on regex scripts scraping screens, lots of stuff could progress much faster.
He’s right, particularly from Juniper’s perspective; they were the first vendor to use a data-driven approach to show commands. Unfortunately, we’re still not living in a perfect world:
OSPF Loop Prevention with Area Range Summary LSAs
In a previous blog post, I described how OSPF route selection rules prevent a summary LSA from being inserted back into an area from which it was generated. That works nicely for area prefixes turned directly into summary LSAs, but how does the loop prevention logic work for summarized prefixes (what OSPF calls area ranges)?
TL&DR: It doesn’t, unless… ;)