This is the Source code for CIDR Trainer. CIDR Trainer is in the iOS / MacOS App store: https://apps.apple.com/us/app/cidr-trainer/id1608806016 It uses directed drills and help to train people to calculate IPv4 and IPv6 subnets. App store version permits 20 attempts / drill for free, with a full unlock made available as an in-app purchase (which is now also free). The app could be improved. Examples of improvements include "flair", localization, improved "help" explanations, full coverage of IPv6, and accessibility. I welcome pull-requests and am happy to add significant contributors to the credits file. Feel free to contact me at feedback@networkmom.net. Darrell Root for Network Mom LLC For support email "networkmom AT proton.me"