IP ranges do not round trip correctly as strings

We are seeing this:

const cidr = "1.2.3.4/5";
IPv4CidrRange.fromCidr(cidr).toCidrString();

// -> 0.0.0.0/5

The CIDR we put in (“1.2.3.4/5”) is not the CIDR we get out (“0.0.0.0/5”)

I can see roughly why this is happening, as /5 is a very big range.

The problem for us is that 1.2.3.4/5 is used as an internal placeholder in CDK: https://github.com/aws/aws-cdk/blob/cea1039e3664fdfa89c6f00cdaeb1a0185a12678/packages/%40aws-cdk/aws-ec2/lib/vpc.ts#L2198

We are seeing tests break when we render our templates and try and round trip things.

What would “you expect to happen” if you put string into a CIDR, then call toCidrString on it? I would say it should be the same, but I am sure there are some optimisations going on internally that are causing this.

[dadepo]

Should now be fixed in v1.5.0

[hlascelles]

Terrific thank you. Thanks for this package, it’s very useful!