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.

For example, imagine you want to have a simple topology with two BGP-speaking routers, each in its own autonomous system. This is how you could describe that in orthodox YAML:

defaults:
  device: eos
  
nodes:
  r1:
    bgp:
      as: 65000
  r2:
    bgp:
      as: 65002

Now let’s introduce some shortcuts:

defaults.device: eos

nodes:
  r1:
    bgp.as: 65000
  r2:
    bgp.as: 65002

I’m sure you get the idea. The only thing you have to be careful about³: don’t mix the YAML dictionary notation with the shortcuts for the same object. I opened an issue months ago. Jeroen provided a fix soon after that, and we can only hope it will eventually get merged into the next release.

Anyway, can we go any further? Of course. How about:

defaults.device: eos

nodes:
  r1.bgp.as: 65000
  r2.bgp.as: 65002

Finally, let’s add a link with fixed IPv4 addresses to the topology, using the trick we just learned:

defaults.device: eos

nodes:
  r1.bgp.as: 65000
  r2.bgp.as: 65002

links:
- r1.ipv4: 10.1.0.1/24
  r2.ipv4: 10.1.0.2/24

OK, here’s another one in case you don’t like the hard-coded IP addresses (it uses a hard-coded IPv4 prefix, though):

defaults.device: eos

nodes:
  r1.bgp.as: 65000
  r2.bgp.as: 65002

links:
- prefix.ipv4: 10.1.0.0/24
  r1.ipv4: 1
  r2.ipv4: 2

Have fun ;) And if you create something cool with netlab, do let me know!