Change "Prefix Too Large" Behavior?

[cooperwalbrun]

I will need to gather some input from others on this. The idea is that instead of erroring out when an "invalid" prefix is specified, e.g.:

$ aws-cidr-finder --profile myprofile --prefix 18
Desired prefix (18) is incompatible with the available CIDR blocks!
Encountered a CIDR whose prefix is 19, which is higher than 18. Offending CIDR: 172.31.96.0/19
Run the command again without the --prefix argument to see the full list.

...the results list could just be scrubbed of any CIDRs that do not satisfy the criteria. For example, if the aws-cidr-finder command would return 172.0.0.0/20, 172.0.16.0/18, 172.45.0.0/32 and we specify --prefix 18, the only result would be 172.0.16.0/18 because that is the only returned CIDR that is large enough to have the desired prefix.

[cooperwalbrun]

An alternative to changing the behavior of --prefix is adding an additional flag which will allow the behavior described above. What I have in mind is --filter, e.g.:

aws-cidr-finder --profile myprofile --prefix 18 --filter

[DacoDev]

An alternative to changing the behavior of --prefix is adding an additional flag which will allow the behavior described above. What I have in mind is --filter, e.g.:

aws-cidr-finder --profile myprofile --prefix 18 --filter

Adding filter seems like a good solution, but also I don't know if someone looking for a subnet with a certain CIDR would care if it runs into a block it checked that was of an incompatible size, only if there were no available blocks for their specified prefix.

Of course, this is from my perspective and use-case where I'm breaking up a VPC to create a subnet with Terraform at launch time. I found this issue because I got the error you listed; the first available block sequentially in my VPC is a /28, but I'm looking for /25s.

Whatever you decide, thanks for making and working on this!

[cooperwalbrun]

Thanks for the input @DacoDev. I will make this change.

Edit: the change described in the root post of this issue is now available in aws-cidr-finder v0.1.2.

[DacoDev]

Thank you @cooperwalbrun!