cidr-deny-allow-transformer

This is a NPM library that allows you to transform a subset of denied CIDRs within a larger CIDR into a list of allowed CIDRs.

Less talk, more library

npm install cidr-deny-allow-transformer

Keep track of the versions with the changelog.

Motivation

If you're deploying infrastructure-as-code to AWS, you come across SecurityGroups with their corresponding ingress configuration. SecurityGroups can only be configured to allow but not to deny certain traffic.

In reality, you often want to deny certain CIDRs (e.g. those containing IPs of gateways that are exposed to the internet) while you want to allow the rest of a larger CIDR (e.g. you company network).

With this small library you can do exactly that - pass a CIDR and a subset of denied CIDRs and you'll get all allowed CIDRs.

I recommend using this library, if you're using the AWS-CDK and are dealing with SecurityGroups.

Usage

Import the transformer...

import { CidrDenyAllowTransformer } from 'cidr-deny-allow-transformer';

... and find your allowed CIRDs:

const allowedCidrs = CidrDenyAllowTransformer.findAllowedCidrs('192.160.0.0/12', '192.162.0.0/18', '192.172.0.0/23', '192.172.56.0/21');