Oh no…. Not another CIDR calculator, because there really are a bunch.

Allow me to advocate for my app CIDRizer, focused on CIDR space coverage. If one has a CIDR block (account, VPC, etc.), and their engineers take a little slice here and there (of varying mask size and probably not consecutive), how can one actually see what’s left?

Example (CIDRizer input):

10.10.10.0/24   # Overall Account/VPC

10.10.10.32/29  # Jim's tests
10.10.10.128/29 # dev4a
10.10.10.160/28 # Ruth's team

… can be completely covered/represented as follows (CIDRizer output):

Account

CIDR	2^(32-n)	Avail.	First	Last
10.10.10.0/24	256	254	10.10.10.0	10.10.10.255

Simplest Coverage CIDR Blocking (SCCB)

CIDR	2^(32-n)	Avail.	First	Last
10.10.10.0/27	32	30	10.10.10.0	10.10.10.31
10.10.10.32/29	8	6	10.10.10.32	10.10.10.39
10.10.10.40/29	8	6	10.10.10.40	10.10.10.47
10.10.10.48/28	16	14	10.10.10.48	10.10.10.63
10.10.10.64/26	64	62	10.10.10.64	10.10.10.127
10.10.10.128/29	8	6	10.10.10.128	10.10.10.135
10.10.10.136/29	8	6	10.10.10.136	10.10.10.143
10.10.10.144/28	16	14	10.10.10.144	10.10.10.159
10.10.10.160/28	16	14	10.10.10.160	10.10.10.175
10.10.10.176/28	16	14	10.10.10.176	10.10.10.191
10.10.10.192/26	64	62	10.10.10.192	10.10.10.255

Algorithm & Code

I have made the repository public, with an ISC license. This unit test file details what the core algorithm is doing (and can be run via npm test), the rest of the project’s code is simply enabling it as a NodeJS web app.

Run / Deploy

As usual npm start, but there’s a serverless.yml which is what I’ve used to deploy it to my domain CIDRizer.com.

That’s it. My contribution to the CIDR calculator space.