Finding immediate parent prefix for an IP address

[Tom Kivlin]

Hi - I am trying to work out if there is a shortcut to getting the most immediate parent prefix for a particular CIDR from the API?

e.g. I can call the following API: https://netbox/api/ipam/prefixes/?contains=10.50.130.22%2F23

And I will get 3 prefixes back:

"prefix": "10.50.0.0/16",

"prefix": "10.50.128.0/17",

"prefix": "10.50.130.0/23",

Obviously I could do some handling my side to check the netmask etc. to try and match them up but I wondered if there was a "magic" API query that exists to do this?

[Brian Candler]

Sort by prefix length and take the last.  They do appear to be already sorted in your case, but I don't know if that's accidental or guaranteed.

The Netbox data model duplicates prefix information, because every IP address object also stores a prefix length.  Given that you're looking for the prefix containing "10.50.130.22/23", you already know implicitly that it should be 10.50.130.0/23, without even making any API query.

In practice, I find people wrongly entering "/24" all the time, regardless of the true prefix length - so don't rely on it.

[Tom Kivlin]

Thanks, Brian - you got me thinking about this in a different way.  The background to this was that I am using Ansible to automate some infra.  Turns out Ansible has a built-in filter, ipsubnet(), which I can use to do exactly what you mentioned.

Ta,

Tom