CIDR Trainer is live in both the MacOS and iOS App stores. It uses directed training drills and help files to each IPv4 and IPv6 addressing and subnetting. 50 drills of increasing difficulty with help files. Each drill is free to try 20 times. $2 forever unlock.
100% SwiftUI app (using Catalyst on MacOS for an iPad-like interface).
Approximately 47% of users in the US access Google via IPv6. You probably recognize and understand 32-bit IPv4 addresses such as 192.168.3.35. It is time to recognize and understand 128-bit IPv6 addresses such as 2001:db8:4800:1a52:2e:7813:f527:313e
There is a substantial probability you already have dual-stack IPv4/IPv6 connectivity at home! You can find out at https://test-ipv6.com
Google IPv6 deployment stats by country at https://www.google.com/intl/en/ipv6/statistics.html#tab=per-country-ipv6-adoption